Collective behavior

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Collective_behavior

The expression collective behavior was first used by Franklin Henry Giddings (1908) and employed later by Robert E. Park and Burgess (1921), Herbert Blumer (1939), Ralph Turner and Lewis Killian (1957), and Neil Smelser (1962) to refer to social processes and events which do not reflect existing social structure (laws, conventions, and institutions), but which emerge in a "spontaneous" way. Use of the term has been expanded to include reference to cells, social animals like birds and fish, and insects including ants (Gordon 2014). Collective behavior takes many forms but generally violates societal norms (Miller 2000; Locher 2002). Collective behavior can be tremendously destructive, as with riots or mob violence, silly, as with fads, or anywhere in between. Collective behavior is always driven by group dynamics, encouraging people to engage in acts they might consider unthinkable under typical social circumstances (Locher 2002).

Defining the field

Turner and Killian (1957) were the first sociologists to back their theoretical propositions with visual evidence in the form of photographs and motion pictures of collective behavior in action. Prior to that sociologists relied heavily upon eyewitness accounts, which turned out to be far less reliable than one would hope.

Turner and Killian's approach is based largely upon the arguments of Blumer, who argued that social "forces" are not really forces. The actor is active: He creates an interpretation of the acts of others, and acts on the basis of this interpretation.

Examples

Here are some instances of collective behavior: the Los Angeles riot of 1992, the hula-hoop fad of 1958, the stock market crashes of 1929, and the "phantom gasser" episodes in Virginia in 1933–34 and Mattoon, IL in 1944 (Locher 2002; Miller 2000). The claim that such diverse episodes all belong to a single field of inquiry is a theoretical assertion, and not all sociologists would agree with it. But Blumer and Neil Smelser did agree, as did others, indicating that the formulation has satisfied some leading sociological thinkers.

Four forms

Although there are several other schema that may be used to classify forms of collective behavior the following four categories from Blumer (1939) are generally considered useful by most sociologists.

The crowd

Scholars differ about what classes of social events fall under the rubric of collective behavior. In fact, the only class of events which all authors include is crowds. Clark McPhail is one of those who treats crowds and collective behavior as synonyms. Although some consider McPhail's work (McPhail 1991) overly simplistic (Locher 2002), his important contribution is to have gone beyond the speculations of others to carry out pioneering empirical studies of crowds. He finds them to form an elaborate set of types.

The classic treatment of crowds is Gustave LeBon, The Crowd: A Study of the Popular Mind (LeBon 1896), in which the author interpreted the crowds of the French Revolution as irrational reversions to animal emotion, and inferred from this that such reversion is characteristic of crowds in general. LeBon believed that crowds somehow induced people to lose their ability to think rationally and to somehow recover this ability once they had left the crowd. He speculated, but could not explain how this might occur. Freud expressed a similar view in Group Psychology and the Analysis of the Ego (1922). Such authors have thought that their ideas were confirmed by various kinds of crowds, one of these being the economic bubble. In Holland, during the tulip mania (1637), the prices of tulip bulbs rose to astronomical heights. An array of such crazes and other historical oddities is narrated in Charles MacKay's Extraordinary Popular Delusions and the Madness of Crowds (MacKay 1841).

At the University of Chicago, Robert Park and Herbert Blumer agreed with the speculations of LeBon and other that crowds are indeed emotional. But to them a crowd is capable of any emotion, not only the negative ones of anger and fear.

A number of authors modify the common-sense notion of the crowd to include episodes during which the participants are not assembled in one place but are dispersed over a large area. Turner and Killian refer to such episodes as diffuse crowds, examples being Billy Graham's revivals, panics about sexual perils, witch hunts and Red scares. Their expanded definition of the crowd is justified if propositions which hold true among compact crowds do so for diffuse crowds as well.

Some psychologists have claimed that there are three fundamental human emotions: fear, joy, and anger. Neil Smelser, John Lofland, and others have proposed three corresponding forms of the crowd: the panic (an expression of fear), the craze (an expression of joy), and the hostile outburst (an expression of anger). Each of the three emotions can characterize either a compact or a diffuse crowd, the result being a scheme of six types of crowds. Lofland has offered the most explicit discussion of these types.

The public

Boom distinguishes the crowd, which expresses a common emotion, from a public, which discusses a single issue. Thus, a public is not equivalent to all of the members of a society. Obviously, this is not the usual use of the word, "public." To Park and Blumer, there are as many publics as there are issues. A public comes into being when discussion of an issue begins, and ceases to be when it reaches a decision on it.

The mass

To the crowd and the public Blumer adds a third form of collective behavior, the mass. It differs from both the crowd and the public in that it is defined not by a form of interaction but by the efforts of those who use the mass media to address an audience. The first mass medium was printing.

The social movement

We change intellectual gears when we confront Blumer's final form of collective behavior, the social movement. He identifies several types of these, among which are active social movements such as the French Revolution and expressive ones such as Alcoholics Anonymous. An active movement tries to change society; an expressive one tries to change its own members.

The social movement is the form of collective behavior which satisfies least well the first definition of it which was offered at the beginning of this article. These episodes are less fluid than the other forms, and do not change as often as other forms do. Furthermore, as can be seen in the history of the labor movement and many religious sects, a social movement may begin as collective behavior but over time become firmly established as a social institution.

For this reason, social movements are often considered a separate field of sociology. The books and articles about them are far more numerous than the sum of studies of all the other forms of collective behavior put together. Social movements are considered in many Wikipedia articles, and an article on the field of social movements as a whole would be much longer than this essay.

The study of collective behavior spun its wheels for many years, but began to make progress with the appearance of Turner and Killian's "Collective Behavior" (1957) and Smelser's Theory of Collective Behavior (1962). Both books pushed the topic of collective behavior back into the consciousness of American sociologists and both theories contributed immensely to our understanding of collective behavior (Locher 2002; Miller 2000). Social disturbances in the U. S. and elsewhere in the late '60s and early '70s inspired another surge of interest in crowds and social movements. These studies presented a number of challenges to the armchair sociology of earlier students of collective behavior.

Theories developed to explain

Social scientists have developed theories to explain crowd behavior.

1. Contagion Theory – the Contagion Theory was formulated by Gustave Le Bon. According to Le Bon crowds exert a hypnotic influence over their members. Shielded by their anonymity, large numbers of people abandon personal responsibility and surrender to the contagious emotions of the crowd. A crowd thus assumes a life of its own, stirring up emotions and driving people toward irrational, even violent action (LeBon 1896). Le Bon's Theory, although one of the earliest explanations of crowd behavior, is still accepted by many people outside of sociology (Castellano, Fortunato & Loreto 2009; Braha 2012; Braha & Aguiar 2017). However, critics argue that the "collective mind" has not been documented by systematic studies. Furthermore, although collective behavior may involve strong emotions, such feelings are not necessarily irrational. Turner and Killian (1957) argue convincingly that the "contagion" never actually occurs and participants in collective behavior do not lose their ability to think rationally.
2. Convergence Theory – whereas the Contagion Theory states that crowds cause people to act in a certain way, Convergence theory states that people who want to act in a certain way come together to form crowds. Developed by Floyd Allport (1924) and later expanded upon by Neil Miller and John Dollard (1941) as "Learning Theory," the central argument of all convergence theories is that collective behavior reveals the otherwise hidden tendencies of the individuals who take part in the episode. It asserts that people with similar attributes find other like-minded persons with whom they can release these underlying tendencies. People sometimes do things in a crowd that they would not have the courage to do alone because crowds can diffuse responsibility but the behavior itself is claimed to originate within the individuals. Crowds, in addition, can intensify a sentiment simply by creating a critical mass of like-minded people.
3. Emergent-Norm Theory – according to Ralph Turner and Lewis Killian (1957), crowds begin as collectivities composed of people with mixed interests and motives. Especially in the case of less stable crowds—expressive, acting and protest crowds—norms may be vague and changing, as when one person decides to break the glass windows of a store and others join in and begin looting merchandise. When people find themselves in a situation that is vague, ambiguous, or confusing new norms "emerge" on the spot and people follow those emergent norms, which may be at odds with normal social behavior. Turner and Killian further argue that there are several different categories of participants, all of whom follow different patterns of behavior due to their differing motivations.
4. Value-added Theory – Neil Smelser (1962) argues that collective behavior is actually a sort of release valve for built-up tension ("strain") within the social system, community, or group. If the proper determinants are present then collective behavior becomes inevitable. Conversely, if any of the key determinants are not present no collective behavior will occur unless and until the missing determinants fall into place. These are primarily social, although physical factors such as location and weather may also contribute to or hinder the development of collective behavior.
5. Complex Adaptive Systems theory – Dutch scholar Jaap van Ginneken claims that contagion, convergence and emergent norms are just instances of the synergy, emergence and autopoiesis or self-creation of patterns and new entities typical for the newly discovered meta-category of complex adaptive systems. This also helps explain the key role of salient details and path-dependence in rapid shifts.

Quorum sensing

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Quorum_sensing 

In biology, quorum sensing is the ability to detect and to respond to cell population density by gene regulation. As one example, quorum sensing (QS) enables bacteria to restrict the expression of specific genes to the high cell densities at which the resulting phenotypes will be most beneficial. Many species of bacteria use quorum sensing to coordinate gene expression according to the density of their local population. In a similar fashion, some social insects use quorum sensing to determine where to nest. Quorum sensing may also be useful for cancer cell communications.

In addition to its function in biological systems, quorum sensing has several useful applications for computing and robotics. In general, quorum sensing can function as a decision-making process in any decentralized system in which the components have: (a) a means of assessing the number of other components they interact with and (b) a standard response once a threshold number of components is detected.

Discovery

Quorum sensing was first reported in 1970, by Kenneth Nealson, Terry Platt, and J. Woodland Hastings, who observed what they described as a conditioning of the medium in which they had grown the photoluminescent marine bacterium Aliivibrio fischeri. These bacteria did not synthesize luciferase—and therefore did not luminesce—in freshly inoculated culture but only after the bacterial population had increased significantly. Because they attributed this conditioning of the medium to the growing population of cells itself, they referred to the phenomenon as autoinduction.

Bacteria

Some of the best-known examples of quorum sensing come from studies of bacteria. Bacteria use quorum sensing to regulate certain phenotype expressions, which in turn, coordinate their behaviours. Some common phenotypes include biofilm formation, virulence factor expression, and motility. Certain bacteria are able to use quorum sensing to regulate bioluminescence, nitrogen fixation and sporulation.

The quorum-sensing function is based on the local density of the bacterial population in the immediate environment. It can occur within a single bacterial species, as well as between diverse species. Both Gram-positive and gram-negative bacteria use quorum sensing, but there are some major differences in their mechanisms.

Mechanism

For the bacteria to use quorum sensing constitutively, they must possess three characteristics: to secrete a signaling molecule, an autoinducer, to detect the change in concentration of signaling molecules, and to regulate gene transcription as a response. This process is highly dependent on the diffusion mechanism of the signaling molecules. QS Signaling molecules are usually secreted at a low level by individual bacteria. At low cell density, the molecules may just diffuse away. At high cell density, the local concentration of signaling molecules may exceed its threshold level, and trigger changes in gene expressions.

Gram-positive Bacteria

Gram-positive bacteria use autoinducing peptide (AIP) as their autoinducers.

When gram-positive bacteria detect high concentration of AIP in their environment, AIP binds to a receptor to activate a kinase. The kinase phosphorylates a transcription factor, which regulates gene transcription. This is called a two-component system.

Another possible mechanism is that AIP is transported into the cytosol, and binds directly to a transcription factor to initiate or inhibit transcription.

Gram-negative Bacteria

Gram-negative bacteria produce N-acyl homoserine lactones (AHL) as their signaling molecule. Usually AHLs do not need additional processing, and bind directly to transcription factors to regulate gene expression.

Some gram-negative bacteria may use the two-component system as well.

Quorum sensing of Gram-Negative cell

Examples

Aliivibrio fischeri

The bioluminescent bacterium A. fischeri is the first organism in which QS was observed. It lives as a mutualistic symbiont in the photophore (or light-producing organ) of the Hawaiian bobtail squid. When A. fischeri cells are free-living (or planktonic), the autoinducer is at low concentration, and, thus, cells do not show luminescence. However, when the population reaches the threshold in the photophore (about 10¹¹ cells/ml), transcription of luciferase is induced, leading to bioluminescence. In V. fischeri bioluminescence is regulated by AHLs ( N-acyl-homoserine lactones) which is a product of LuxI gene whose transcription is regulated by the LuxR activator. LuxR works only when AHLs binds to the LuxR.

Curvibacter sp.

Curvibacter sp. is a Gram-negative curved rod-formed bacteria which is the main colonizer of the epithelial cells surfaces of the early branching metazoan Hydra vulgaris. Sequencing the complete genome uncovered a circular chromosome (4.37 Mb), a plasmid (16.5 kb), and two operons coding each for an AHL (N-acyl-homoserine lactone) synthase (curI1 and curI2) and an AHL receptor (curR1 and curR2). Moreover, a study showed that host associated bacteria Curvibacter produce a broad spectrum of AHL, explaining the presence of those operons. As mentioned before, AHL are the quorum sensing molecules of Gram-negative bacteria, which means Curvibacter has a quorum sensing activity.

Even though their function in host-microbe interaction is largely unknown, Curvibacter quorum-sensing signals were relevant for host-microbe interactions. Indeed, due to the oxidoreductase activity of Hydra, there is a modification of AHL signalling molecules, to know 3-oxo-homoserine lactone into 3-hydroxy-homoserine lactone, which leads to a different host-microbe interaction. On one hand, a phenotypic switch of the colonizer Curvibacter takes place. The most likely explanation is that the binding of 3-oxo-HSL and 3-hydroxy-HSL causes different conformational changes in the AHL receptors curR1 and curR2. As a result, there is a different DNA-binding motif affinity and thereby different target genes are activated. On the other hand, this switch modifies its ability to colonize the epithelial cell surfaces of Hydra vulgaris. Indeed, one explanation is that with a 3-oxo-HSL quorum-sensing signal, there is an up-regulation of flagellar assembly. Yet, flagellin, the main protein component of flagella, can act as an immunomodulator and activate the innate immune response in Hydra. Therefore, bacteria have less chance to evade the immune system and to colonize host tissues. Another explanation is that 3-hydroxy-HSL induces carbon metabolism and fatty acid degradation genes in Hydra. This allows the bacterial metabolism to adjust itself to the host growth conditions, which is essential for the colonization of the ectodermal mucus layer of Hydra.

Escherichia coli

In the Gram-negative bacterium Escherichia coli (E. coli), cell division may be partially regulated by AI-2-mediated quorum sensing. This species uses AI-2, which is produced and processed by the lsr operon. Part of it encodes an ABC transporter, which imports AI-2 into the cells during the early stationery (latent) phase of growth. AI-2 is then phosphorylated by the LsrK kinase, and the newly produced phospho-AI-2 can be either internalized or used to suppress LsrR, a repressor of the lsr operon (thereby activating the operon). Transcription of the lsr operon is also thought to be inhibited by dihydroxyacetone phosphate (DHAP) through its competitive binding to LsrR. Glyceraldehyde 3-phosphate has also been shown to inhibit the lsr operon through cAMP-CAPK-mediated inhibition. This explains why, when grown with glucose, E. coli will lose the ability to internalize AI-2 (because of catabolite repression). When grown normally, AI-2 presence is transient.

E. coli and Salmonella enterica do not produce AHL signals commonly found in other Gram-negative bacteria. However, they have a receptor that detects AHLs from other bacteria and change their gene expression in accordance with the presence of other "quorate" populations of Gram-negative bacteria.

Gram positive bacteria quorum sensing

Salmonella enterica

Salmonella encodes a LuxR homolog, SdiA, but does not encode an AHL synthase. SdiA detects AHLs produced by other species of bacteria including Aeromonas hydrophila, Hafnia alvei, and Yersinia enterocolitica. When AHL is detected, SdiA regulates the rck operon on the Salmonella virulence plasmid (pefI-srgD-srgA-srgB-rck-srgC) and a single gene horizontal acquisition in the chromosome srgE. Salmonella does not detect AHL when passing through the gastrointestinal tracts of several animal species, suggesting that the normal microbiota does not produce AHLs. However, SdiA does become activated when Salmonella transits through turtles colonized with Aeromonas hydrophila or mice infected with Yersinia enterocolitica. Therefore, Salmonella appears to use SdiA to detect the AHL production of other pathogens rather than the normal gut flora.

Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa uses quorum sensing to coordinate the formation of biofilm, swarming motility, exopolysaccharide production, virulence, and cell aggregation. These bacteria can grow within a host without harming it until they reach a threshold concentration. Then they become aggressive, developing to the point at which their numbers are sufficient to overcome the host's immune system, and form a biofilm, leading to disease within the host as the biofilm is a protective layer encasing the bacteria population. Another form of gene regulation that allows the bacteria to rapidly adapt to surrounding changes is through environmental signaling. Recent studies have discovered that anaerobiosis can significantly impact the major regulatory circuit of quorum sensing. This important link between quorum sensing and anaerobiosis has a significant impact on the production of virulence factors of this organism. It is hoped that the therapeutic enzymatic degradation of the signaling molecules will prevent the formation of such biofilms and possibly weaken established biofilms. Disrupting the signaling process in this way is called quorum sensing inhibition.

Acinetobacter sp.

It has recently been found that Acinetobacter sp. also show quorum sensing activity. This bacterium, an emerging pathogen, produces AHLs. Acinetobacter sp. shows both quorum sensing and quorum quenching activity. It produces AHLs and also, it can degrade the AHL molecules as well.

Aeromonas sp.

This bacterium was previously considered a fish pathogen, but it has recently emerged as a human pathogen. Aeromonas sp. have been isolated from various infected sites from patients (bile, blood, peritoneal fluid, pus, stool and urine). All isolates produced the two principal AHLs, N-butanoylhomoserine lactone (C4-HSL) and N-hexanoyl homoserine lactone (C6-HSL). It has been documented that Aeromonas sobria has produced C6-HSL and two additional AHLs with N-acyl side chain longer than C6.

Yersinia

The YenR and YenI proteins produced by the gammaproteobacterium Yersinia enterocolitica are similar to Aliivibrio fischeri LuxR and LuxI. YenR activates the expression of a small non-coding RNA, YenS. YenS inhibits YenI expression and acylhomoserine lactone production. YenR/YenI/YenS are involved in the control of swimming and swarming motility.

Molecules involved

Three-dimensional structures of proteins involved in quorum sensing were first published in 2001, when the crystal structures of three LuxS orthologs were determined by X-ray crystallography. In 2002, the crystal structure of the receptor LuxP of Vibrio harveyi with its inducer AI-2 (which is one of the few biomolecules containing boron) bound to it was also determined. Many bacterial species, including E. coli, an enteric bacterium and model organism for Gram-negative bacteria, produce AI-2. A comparative genomic and phylogenetic analysis of 138 genomes of bacteria, archaea, and eukaryotes found that "the LuxS enzyme required for AI-2 synthesis is widespread in bacteria, while the periplasmic binding protein LuxP is present only in Vibrio strains," leading to the conclusion that either "other organisms may use components different from the AI-2 signal transduction system of Vibrio strains to sense the signal of AI-2 or they do not have such a quorum sensing system at all." Farnesol is used by the fungus Candida albicans as a quorum sensing molecule that inhibits filamentation.

A database of quorum-sensing peptides is available under the name Quorumpeps.

Certain bacteria can produce enzymes called lactonases that can target and inactivate AHLs. Researchers have developed novel molecules which block the signalling receptors of bacteria (Quorum quenching). mBTL is a compound that has been shown to inhibit quorum sensing and decrease the amount of cell death by a significant amount. Additionally, researchers are also examining the role of natural compounds (such as caffeine) as potential quorum sensing inhibitors. Research in this area has been promising and could lead to the development of natural compounds as effective therapeutics.

Evolution

Sequence analysis

The majority of quorum sensing systems that fall under the "two-gene" (an autoinducer synthase coupled with a receptor molecule) paradigm as defined by the Vibrio fischeri system occur in the Gram-negative Proteobacteria. A comparison between the Proteobacteria phylogeny as generated by 16S ribosomal RNA sequences and phylogenies of LuxI-, LuxR-, or LuxS-homologs shows a notably high level of global similarity. Overall, the quorum sensing genes seem to have diverged along with the Proteobacteria phylum as a whole. This indicates that these quorum sensing systems are quite ancient, and arose very early in the Proteobacteria lineage.

Although examples of horizontal gene transfer are apparent in LuxI, LuxR, and LuxS phylogenies, they are relatively rare. This result is in line with the observation that quorum sensing genes tend to control the expression of a wide array of genes scattered throughout the bacterial chromosome. A recent acquisition by horizontal gene transfer would be unlikely to have integrated itself to this degree. Given that the majority of autoinducer–synthase/receptor occurs in tandem in bacterial genomes, it is also rare that they switch partners and so pairs tend to co-evolve.

In quorum sensing genes of Gammaproteobacteria, which includes Pseudomonas aeruginosa and Escherichia coli, the LuxI/LuxR genes form a functional pair, with LuxI as the auto-inducer synthase and LuxR as the receptor. Gamma Proteobacteria are unique in possessing quorum sensing genes, which, although functionally similar to the LuxI/LuxR genes, have a markedly divergent sequence. This family of quorum-sensing homologs may have arisen in the gamma Proteobacteria ancestor, although the cause of their extreme sequence divergence yet maintenance of functional similarity has yet to be explained. In addition, species that employ multiple discrete quorum sensing systems are almost all members of the gamma Proteobacteria, and evidence of horizontal transfer of quorum sensing genes is most evident in this class.

Interaction of quorum-sensing molecules with mammalian cells and its medical applications

Next to the potential antimicrobial functionality, quorum-sensing derived molecules, especially the peptides, are being investigated for their use in other therapeutic domains as well, including immunology, central nervous system disorders and oncology. Quorum-sensing peptides have been demonstrated to interact with cancer cells, as well as to permeate the blood-brain barrier permeation reaching the brain parenchyma.

Viruses

A mechanism involving Arbitrium has recently been described in bacteriophages infecting several Bacillus species. The viruses communicate with each other to ascertain their own density compared to potential hosts. They use this information to decide whether to enter a lytic or lysogenic life-cycle.

Archaea

Examples

Methanosaeta harundinacea 6Ac

Methanosaeta harundinacea 6Ac, a methanogenic archaeon, produces carboxylated acyl homoserine lactone compounds that facilitate the transition from growth as short cells to growth as filaments.

Plants

Quorum sensing could be described when it was known that bacteria possess the ability to communicate. In the last few years, interactions between bacteria and eukaryotic hosts, such as plants, have been shown. These interactions are facilitated by quorum-sensing molecules and play a major role in maintaining the pathogenicity of bacteria towards other hosts, such as humans. This mechanism can be understood by looking at the effects of N-Acyl homoserine lactone (AHL), one of the quorum sensing-signaling molecules in gram-negative bacteria, on plants. The model organism used is Arabidopsis thaliana.

The role of AHLs having long carbon-chains (C12, C14), which have an unknown receptor mechanism, is less well understood than AHLs having short carbon-chains (C4, C6, C8), which are perceived by the G protein-coupled receptor. A phenomenon called "AHL priming", which is a dependent signalling pathway, enhanced our knowledge of long-chain AHLs. The role of quorum-sensing molecules was better explained according to three categories: host physiology–based impact of quorum sensing molecules; ecological effects; and cellular signaling. Calcium signalling and calmodulin have a large role in short-chain AHLs response in Arabidopsis. Research was also conducted on barley and crop yam bean that reveals the AHLs determining the detoxification enzymes called GST were found less in yam bean.

Quorum sensing-based regulatory systems are necessary to plant-disease-causing bacteria. Looking towards developing new strategies based on plant-associated microbiomes, the aim of further study is to improve the quantity and quality of the food supply. Further research into this inter-kingdom communication also enhances the possibility of learning about quorum sensing in humans.

Quorum quenching

Quorum quenching is the process of preventing quorum sensing by disrupting signalling. This is achieved by inactivating signalling enzymes, by introducing molecules that mimic signalling molecules and block their receptors, by degrading signalling molecules themselves, or by a modification of the quorum sensing signals due to an enzyme activity.

Inhibition of signalling molecules

Closantel and triclosan are known inhibitors of quorum sensing enzymes. Closantel induces aggregation of the histidine kinase sensor in two-component signalling. The latter disrupts the synthesis of a class of signalling molecules known as N-acyl homoserine lactones (AHLs) by blocking the enoyl-acyl carrier protein (ACP) reductase.

Mimicking of signalling molecules

Two groups of well-known mimicking molecules include halogenated furanones, which mimic AHL molecules, and synthetic Al peptides (AIPs), which mimic naturally occurring AIPs. These groups inhibit receptors from binding substrate or decrease the concentration of receptors in the cell. Furanones have also been found to act on AHL-dependant transcriptional activity, whereby the half life of the autoinducer-binding LuxR protein is significantly shortened.

Degradation of signalling molecules

Recently, a well-studied quorum quenching bacterial strain (KM1S) was isolated and its AHL degradation kinetic was studied using rapid resolution liquid chromatography (RRLC). RRLC efficiently separates components of a mixture to a high degree of sensitivity, based on their affinities for different liquid phases. It was found that the genome of this strain encoded an inactivation enzyme with distinct motifs targeting the degradation of AHLs.

Modification of signalling molecules

As mentioned before, N-acyl-homoserine lactones (AHL) are the quorum sensing signaling molecules of the Gram-negative bacteria. However, these molecules may have different functional groups on their acyl chain, and also a different length of acyl chain. Therefore, there exist many different AHL signaling molecules, for example, 3-oxododecanoyl-L-homoserine lactone (3OC12-HSL) or 3-hydroxydodecanoyl-L-homoserine lactone (3OHC12-HSL). The modification of those quorum sensing (QS) signaling molecules is another sort of quorum quenching. This can be carried out by an oxidoreductase activity. As an example, we will discuss the interaction between a host, Hydra vulgaris, and the main colonizer of its epithelial cell surfaces, Curvibacter sp. Those bacteria produce 3-oxo-HSL quorum sensing molecules. However, the oxidoreductase activity of the polyp Hydra is able to modify the 3-oxo-HSL into their 3-hydroxy-HSL counterparts. We can characterize this as quorum quenching since there is an interference with quorum sensing molecules. In this case, the outcomes are different than just QS inactivation. Indeed, the host modification results in a phenotypic switch of Curvibacter, which modify its ability to colonize the epithelial cell surfaces of Hydra vulgaris.

Applications

Applications of quorum quenching that have been exploited by humans include the use of AHL-degrading bacteria in aquacultures to limit the spread of diseases in aquatic populations of fish, mollusks and crustaceans. This technique has also been translated to agriculture, to restrict the spread of pathogenic bacteria that use quorum sensing in plants. Anti-biofouling is another process that exploits quorum quenching bacteria to mediate the dissociation of unwanted biofilms aggregating on wet surfaces, such as medical devices, transportation infrastructure and water systems. Quorum quenching is recently studied for the control of fouling and emerging contaminants in electro membrane bioreactors (eMBRs) for the advanced treatment of wastewater.

Social insects

Social insect colonies are an excellent example of a decentralized system, because no individual is in charge of directing or making decisions for the colony. Several groups of social insects have been shown to use quorum sensing in a process that resembles collective decision-making.

Examples

Ants

Colonies of the ant Temnothorax albipennis nest in small crevices between rocks. When the rocks shift and the nest is broken up, these ants must quickly choose a new nest to move into. During the first phase of the decision-making process, a small portion of the workers leave the destroyed nest and search for new crevices. When one of these scout ants finds a potential nest, she assesses the quality of the crevice based on a variety of factors including the size of the interior, the number of openings (based on light level), and the presence or absence of dead ants. The worker then returns to the destroyed nest, where she waits for a short period before recruiting other workers to follow her to the nest that she has found, using a process called tandem running. The waiting period is inversely related to the quality of the site; for instance, a worker that has found a poor site will wait longer than a worker that encountered a good site. As the new recruits visit the potential nest site and make their own assessment of its quality, the number of ants visiting the crevice increases. During this stage, ants may be visiting many different potential nests. However, because of the differences in the waiting period, the number of ants in the best nest will tend to increase at the greatest rate. Eventually, the ants in this nest will sense that the rate at which they encounter other ants has exceeded a particular threshold, indicating that the quorum number has been reached. Once the ants sense a quorum, they return to the destroyed nest and begin rapidly carrying the brood, queen, and fellow workers to the new nest. Scouts that are still tandem-running to other potential sites are also recruited to the new nest, and the entire colony moves. Thus, although no single worker may have visited and compared all of the available options, quorum sensing enables the colony as a whole to quickly make good decisions about where to move.

Honey bees

Honey bees (Apis mellifera) also use quorum sensing to make decisions about new nest sites. Large colonies reproduce through a process called swarming, in which the queen leaves the hive with a portion of the workers to form a new nest elsewhere. After leaving the nest, the workers form a swarm that hangs from a branch or overhanging structure. This swarm persists during the decision-making phase until a new nest site is chosen.

The quorum sensing process in honey bees is similar to the method used by Temnothorax ants in several ways. A small portion of the workers leave the swarm to search out new nest sites, and each worker assesses the quality of the cavity it finds. The worker then returns to the swarm and recruits other workers to her cavity using the honey bee waggle dance. However, instead of using a time delay, the number of dance repetitions the worker performs is dependent on the quality of the site. Workers that found poor nests stop dancing sooner, and can, therefore, be recruited to the better sites. Once the visitors to a new site sense that a quorum number (usually 10–20 bees) has been reached, they return to the swarm and begin using a new recruitment method called piping. This vibration signal causes the swarm to take off and fly to the new nest location. In an experimental test, this decision-making process enabled honey bee swarms to choose the best nest site in four out of five trials.

Synthetic biology

Quorum sensing has been engineered using synthetic biological circuits in different systems. Examples include rewiring the AHL components to toxic genes to control population size in bacteria; and constructing an auxin-based system to control population density in mammalian cells. Synthetic quorum sensing circuits have been proposed to enable applications like controlling biofilms or enabling drug delivery.

Computing and robotics

Quorum sensing can be a useful tool for improving the function of self-organizing networks such as the SECOAS (Self-Organizing Collegiate Sensor) environmental monitoring system. In this system, individual nodes sense that there is a population of other nodes with similar data to report. The population then nominates just one node to report the data, resulting in power savings. Ad-hoc wireless networks can also benefit from quorum sensing, by allowing the system to detect and respond to network conditions.

Quorum sensing can also be used to coordinate the behavior of autonomous robot swarms. Using a process similar to that used by Temnothorax ants, robots can make rapid group decisions without the direction of a controller.

Quorum

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Quorum 

Vote cast against Themistocles. A quorum of 6,000 was required for ostracism under the Athenian democracy, according to Plutarch; a similar quorum was necessary in the following century for grants of citizenship.

A quorum is the minimum number of members of a deliberative assembly (a body that uses parliamentary procedure, such as a legislature) necessary to conduct the business of that group. According to Robert's Rules of Order Newly Revised, the "requirement for a quorum is protection against totally unrepresentative action in the name of the body by an unduly small number of persons." In contrast, a plenum is a meeting of the full body or very close to it (excepting perhaps a few members who are ill).

The term quorum is from a Middle English wording of the commission formerly issued to justices of the peace, derived from Latin quorum, "of whom", genitive plural of qui, "who". As a result, quora as plural of quorum is not a valid Latin formation.

In Robert's Rules of Order

According to Robert, Each assembly determines the number of members that constitutes a quorum in its governing documents (such as in its constitution, charter, bylaws or standing orders). The quorum may also be set by law. Robert's Rules of Order Newly Revised states that the quorum set in an organization's bylaws "should approximate the largest number that can be depended on to attend any meeting except in very bad weather or other extremely unfavorable conditions."

In the absence of such a provision, a quorum is an assembly whose membership can be determined is a majority of the entire membership. In the meetings of a convention, unless provided otherwise, a quorum is a majority of registered delegates, even if some have departed. In a mass meeting or in an organization in which the membership cannot be accurately determined, the quorum consists of those who attend the meeting.

In committees and boards, a quorum is a majority of the members of the board or committee unless provided otherwise. The board or committee cannot set its own quorum unless given such power. In a committee of the whole or its variants, a quorum is the same as the assembly unless otherwise provided.

In online groups, a quorum has to be determined in a different manner since no one is actually "present". The rules establishing such groups would have to prescribe this determination. An example is that a quorum in such groups could be established as "present" if enough members state that they are "present" at the designated meeting time.

Determination of a quorum

The chairperson of the group has the responsibility to determine if a quorum is present. In addition, any member can raise a point of order about an apparent absence of a quorum. Because it is difficult to determine exactly when a quorum was lost, points of order relating to the absence of a quorum are "generally not permitted to affect prior action; but upon clear and convincing proof, such a point of order can be given effect retrospectively by a ruling of the presiding officer, subject to appeal."

Limited actions in the absence of a quorum

When a quorum is not met, the assembly can only take limited procedural actions. These limited actions are to fix the time to which to adjourn, adjourn, recess, or take measures to obtain a quorum, such as a motion that absent members be contacted during a recess.

Any other business that is conducted is not valid unless it is ratified at a later meeting where a quorum is present. However, there is no obligation to ratify such action and those responsible may be punished for their actions.

Call of the house

In legislatures and other assemblies that have the legal power to compel the attendance of their members, the call of the house procedure may be used to obtain a quorum. This procedure does not exist in ordinary societies, since voluntary associations have no coercive power.

When a call of the house is ordered, the clerk calls the roll of members and then the names of absentees. Members who do not have an excused absence are arrested and brought in. The arrested members may be charged a fee.

By country

Australia

Section 22 and section 39 of the Constitution of Australia set the quorum for sittings of the House of Representatives and Senate at one-third of the whole number of MPs and senators, respectively, but Parliament is permitted to change the quorum for each House by ordinary legislation.

In the House of Representatives, the quorum was amended down to one-fifth by the House of Representatives (Quorum) Act 1989, which means the quorum of the current House of 150 MPs is 30 MPs. In the senate, the quorum was amended down to one-quarter by the Senate (Quorum) Act 1991, so 19 senators is a quorum. The quorum includes the occupant of the Chair and is not reduced by the death or resignation of a member or senator.

If at the beginning of a sitting the quorum is not met, the bells are rung for five minutes and a count is then taken; if the quorum is still not met the sitting is adjourned until the next sitting day. During the sitting, any MP or senator may draw attention to the lack of quorum in which the bells are rung for four minutes, and if a quorum is still not met the sitting is adjourned.

Although quorum-busting is virtually unheard of in Australia, it is not unknown for parties to deliberately use quorum counts as a disruptive tactic and there have been some suggestions to enact rules to restrict this practice; however, this is very difficult due to the explicit mention of a quorum in the constitution. It is considered disorderly to call attention to quorum when one exists and members or senators who do so can be punished.

Austria

In the National Council of Austria at least one-third of the representatives must be present, so that they may decide on a simple law (participation quorum of 33.3%). At least half of the members must participate if a constitutional law should pass the parliament (participation quorum of 50% based on the total number of members). Over and above that, constitutional laws require the consent of at least two-thirds of the members present (quorum agreement of 66.6% based on the number of voting present).

Canada

In Canada, the Constitution Act, 1867 sets quorum for sittings of the House of Commons of Canada at 20 MPs. If a member calls for quorum to be counted and a first count shows there are fewer than 20 members, bells are rung to call in the members; if after 15 minutes there are still fewer than 20 members, the session is adjourned to the next sitting day; the members present sign a roll on the table of the house, and this list is included in the Journal of the House. There is no need for quorum when the attendance of the House is requested in the Senate of Canada, for example, when Royal Assent is being given to bills. The quorum of the Senate is 15.

Provincial and territorial quorums

Province/Territory	Quorum
Alberta	20
British Columbia	10
Manitoba	10
New Brunswick	14
Newfoundland and Labrador	15
Northwest Territories	majority
Nova Scotia	15
Nunavut	majority
Ontario	12
Prince Edward Island	10
Quebec	21
Saskatchewan	15
Yukon	majority

Germany

In the German Bundestag at least half of the members (355 out of 709) must be present so that it is empowered to make resolutions. It is however common that fewer members are present, because they can still make effective decisions as long as no parliamentary group or 5% of the members of the parliament are complaining about the lack of quorum. This, in rare cases, is used by opposition parties to delay votes.

Hong Kong

Article 75 of the Basic Law of Hong Kong stipulates that the quorum required for the meetings of the Legislative Council of Hong Kong (LegCo) as "not less than one-half of its members". Between 1997 and 2012 the quorum was 30, and since 2012 it has been 35. Prior to 1997 transfer of sovereignty over Hong Kong, the quorum was set at 20.

The quorum for the panels, committees and subcommittees is, nevertheless, one-third or three members, whichever the greater, as according to the Rules of Procedure. The three standing committees, namely, the Finance Committee, the Public Accounts Committee and Committee on Members' Interests, is exceptional that the quorums are 9, 3 and 3 respectively.

Quorum-busting was used at least twice since 1997. In 2005, when some pro-democracy members of the council paid a silent tribute to late leader of the People's Republic of China, Zhao Ziyang, against the Rules of Procedure, the president of the council suspended the meeting. When the meeting was recalled, pro-Beijing members refused to return to the chamber, forcing the meeting to be adjourned.

On 27 January 2010, when five pro-democracy members were intending to make their resignation speeches, pro-Beijing members of the council left the chamber as a sign of protest. One of the pro-Beijing members nevertheless stayed in the chamber to call for the quorum to be counted, effectively forcing the meeting to be adjourned. The resignation was intended as a de facto referendum across all five geographical constituencies of the territory, involving the entire electorate, which would not be officially recognised anyway. Most other factions, although against the move by these five Members, stayed in the chamber.

On 2 May 2012, when the LegCo was debating a law change to bar resigning legislators to participate in by-elections in 6 months, effectively discouraging any more "de facto" referenda, some of the five pro-democracy members who resigned constantly issued quorum calls, especially when they were making their resignation speeches intended for 2 years before. In the nine-hour meeting, 23 quorum calls were issued, taking up to 3 hours. When LegCo reconvened on 3 May, it was adjourned for lack of quorum amid a boycott by the pan-democrats. The pro-government members drew a timetable to ensure a quorum, but it failed to prevent another lack of quorum.

On 18 June 2015, when the LegCo was due to vote on a resolution to amend the provisions for the election of the territory's Chief Executive, pro-Beijing members left the chamber to force a quorum roll call to make sure that a sick member could be able to rush back to the chamber. However some of the members stayed behind, citing miscommunication, and the division proceeded with two members above the required quorum of 35. While the resolution was originally predicted to be narrowly defeated due to not able to get super-majority support votes, it turned out to be a landslide defeat.

Quorum-busting and attempts to thwart it are also a common feature during the annual motion debate related to the 1989 Tiananmen massacre moved by pro-democracy Members. The quorum is called to be counted from time to time by the pan-democrats, in order to force the pro-Beijing camp to keep some members in the chamber.

India

Article 100 of the Constitution of India stipulates that at least 10% of total number of members of the House must be present to constitute the quorum to constitute a meeting of either House of Parliament. For example, if the House has the total membership of 250, at least 25 members must be present for the House to proceedings with its business.

If at any time during a meeting of a House there is no quorum, the Chairman has to either adjourn the House or suspend it until there is a quorum.

Ireland

According to the most recent standing orders, published in 2011, the quorum for the Oireachtas, the Irish parliament, for both the lower House, Dáil Éireann, and the upper House, Seanad Éireann, is 20 members.

The chamber of Dáil Éireann is rarely full outside question time, with often just one government representative (often an ordinary Teachta Dála, not a minister) present to answer opposition questions.

Pakistan

Article 55 of the constitutions of Pakistan states that, If at any time during a sitting of the National Assembly the attention of the person presiding is drawn to the fact that less than one-fourth of the total membership of the Assembly is present, he shall either adjourn the Assembly or suspend the meeting until at least one-fourth of such membership is present, which comprises 87 out of total 342.

Philippines

In Congress of the Philippines, half of the membership (13 in the Senate and 153 in the House of Representatives) is needed to muster a quorum. If someone contests the lack of quorum, a roll call shall be done, and if there is indeed less than a majority of members present, the meeting shall be adjourned.

Both majority and minority blocs in Congress have used the lack of quorum in defeating bills that they don't want to be passed without putting it to a vote. After an election during the lame-duck session, quorums are notoriously difficult to muster, more so in the House of Representatives as winning incumbents may opt to go on vacation, and defeated incumbents may opt to not to show up.

Turkey

According to article 96 of the Turkish Constitution, unless otherwise stipulated in the Constitution, the Turkish Grand National Assembly shall convene with at least, one-third of the total number of members (184 out of 550) and shall take decisions by an absolute majority of those present; however, the quorum for decisions can, under no circumstances, be less than a quarter plus one of the total number of members.

Before the constitutional referendum of 2007, there was a quorum of two-thirds required in the Turkish Parliament. The opposition parties used the quorum to deadlock the presidential election of 2007, making it impossible for the parliament to choose a president. As a result, the ruling AK party proposed a referendum to lower the quorum. Nearly seventy percent of the participants supported the constitutional changes.

United Kingdom

In the Parliament of the United Kingdom, the House of Commons has a quorum of 40 MPs, including the Speaker, out of 650 members of the House. There is no need for a quorum to be present at all times. Commons debates could theoretically continue even if just one MP and the Speaker were present. However, if a division is called and fewer than 40 MPs are present, then a decision on the business being considered is postponed and the House moves on to consider the next item of business. The quorum for votes on legislation in the House of Lords is 30, but just three of the 753 peers, including the Lord Speaker, are required to be present for a debate to take place.

Historically, the Quorum was a select group of the Justices of the Peace in each county in early modern Britain. In theory, they were men experienced in law, but many of the Quorum were appointed because of their status. Some legislation required the involvement of a member of the Quorum, (e.g., granting a license to a badger). In practice, they increasingly were not qualified, as the proportion in the Quorum rose faster than the proportion who were called to the bar or practising lawyers. By 1532, an average 45% of Justices of the Peace nationally were of the Quorum. In Somerset, the proportion rose from 52% in 1562 to 93% in 1636. By then, most of those not on the Quorum were new to the bench. Sometimes Justices of the Peace were removed from the Quorum as a disciplinary measure less drastic than removal from the bench.

United Nations

The large deliberative bodies of the United Nations (the General Assembly and Economic and Social Council, as well as their subsidiary organs) generally require the attendance of one-third of the membership (currently 65 states in the General Assembly and 18 in ECOSOC) to conduct most business, but a majority of members (currently 97 states in the General Assembly and 28 states in ECOSOC) in order to take any substantive decisions. The rules of the United Nations Security Council make no provisions for quorum, but nine votes are in all cases required to pass any substantive measure, effectively meaning that a meeting with fewer than nine members in attendance is pointless.

United States

Article I, Section 5, Clause 1 of the United States Constitution provides that "Each House shall be the Judge of the Elections, Returns and Qualifications of its own Members, and a Majority of each shall constitute a Quorum to do Business..." Therefore, in both the House of Representatives and the Senate, a quorum is a simple majority of their respective members. The only exception is that stated in the Twelfth Amendment, which provides that in cases in which no candidate for President of the United States receives a majority in the Electoral College, the election is decided by the House of Representatives, in which case "a quorum for this purpose shall consist of a member or members from two-thirds of the states," and in cases in which no candidate for Vice President of the United States has been elected, the election is decided by the Senate, in which case "a quorum for the purpose shall consist of two-thirds of the whole number of Senators."

The Senate has the additional ordinary requirement in Rule VI of its Standing Rules that "A quorum shall consist of a majority of the Senators duly chosen and sworn."

Call of the house in the United States Senate

In the United States Senate, the procedure was used in the early morning hours of 25 February 1988. Senator Robert C. Byrd of West Virginia, then the Senate Majority Leader, moved a call of the house after the minority Republicans walked out in an attempt to deny the Senate a quorum after Senate aides began bringing cots into the Senate cloakrooms in preparation for an all-night session over campaign finance reform for congressional elections. Byrd's motion was approved 45-3 and arrest warrants were signed for all 46 Republicans. Senate Sergeant-at-Arms Henry K. Giugni and his staff searched the Capitol's corridor and Senate office buildings for absent Senators, and after checking several empty offices, spotted Senator Steve Symms of Idaho, who fled down a hallway and escaped arrest. After a cleaning woman gave a tip that Senator Robert Packwood of Oregon was in his office, Giugni opened the door with a skeleton key. Packwood attempted to shove the door closed, but Giugni and two assistants pushed it open. Packwood was "carried feet-first into the Senate chamber by three plainclothes officers" and sustained bruised knuckles.

Prior to 1988, the last time the procedure had been used was during a 1942 filibuster over civil rights legislation. Southern Democrat senators had spent days filibustering legislation to end poll taxes, just days after midterm elections had resulted in the loss of nine seats. Democratic Majority Leader Alben W. Barkley obtained an order on a Saturday session on 14 November 1942, directing Sergeant at Arms Chesley W. Jurney to round up the five Southern absentees to obtain a quorum. Jurney sent his Deputy Sergeant at Arms, J. Mark Trice, to the apartment of Democratic Senator Kenneth McKellar of Tennessee at the Mayflower Hotel. Then 73 years old and the third-most senior Senator, McKellar was later described by Republican Senator Bill Frist in his book on Tennessee senators as an "extraordinarily shrewd man of husky dimensions with a long memory and a short fuse." Trice called from the lobby, but McKellar refused to answer his phone, so the deputy sergeant at arms walked up to the apartment and convinced the senator's maid to let him in:

When Trice explained that McKellar was urgently needed back at the Capitol, the 73-year-old legislator agreed to accompany him. As they approached the Senate wing, McKellar suddenly realized what was up. An aide later recalled, "His face grew redder and redder. By the time the car reached the Senate entrance, McKellar shot out and barreled through the corridors to find the source of his summons."
Barkley got his quorum...

Quorum-busting

The tactic of quorum-busting—causing a quorum to be prevented from the meeting—has been used in legislative bodies by minorities seeking to block the adoption of some measure they oppose. This generally only happens where the quorum is a super-majority, as quorums of a majority or less of the membership mean that the support of a majority of members is always sufficient for the quorum (as well as for passage). Rules to discourage quorum-busting have been adopted by legislative bodies, such as the call of the house, outlined above.

Quorum-busting has been used for centuries. For instance, during his time in the Illinois Legislature, Abraham Lincoln leapt out of a first story window (the doors of the Capitol had been locked to prevent legislators from fleeing) in a failed attempt to prevent a quorum from being present.

A recent prominent example of quorum-busting occurred during the 2003 Texas redistricting, in which the majority Republicans in the Texas House of Representatives sought to carry out a controversial mid-decade congressional redistricting bill which would have favored Republicans by displacing five Democratic U.S. Representatives from Texas (the Texas Five) from their districts. The House Democrats, certain of defeat if a quorum were present, took a plane to the neighboring state of Oklahoma to prevent a quorum from being present (and thus the passage of the bill). The group gained the nickname "the Killer Ds."

Similarly, the minority Democrats in the Texas Legislature's upper chamber, the Texas Senate, fled to New Mexico to prevent a quorum of the Senate to prevent a redistricting bill from being considered during a special session. The Texas Eleven stayed in New Mexico for 46 days before John Whitmire returned to Texas, creating a quorum. Because there was now no point in staying in New Mexico, the remaining ten members of the Texas Eleven returned to Texas to vote in opposition to the bill.

During the 2011 Wisconsin protests, fourteen Democratic members of the Wisconsin Senate went to Illinois in order to bust the necessary 20-member quorum. Democrats in the Indiana House of Representatives did the same in order to block another union-related bill, causing the legislative clock on the bill to expire. Traveling out of their state placed these legislators beyond the jurisdiction of state troopers who could compel them to return to the chamber.

On 20 June 2019, Oregon Gov. Kate Brown authorized the Oregon State Police to bring Republican state senators, who left the Oregon State Capitol to bust the needed quorum, back to vote on an emissions trading bill that they oppose. State Sen. Brian Boquist said that he told the state police superintendent to "send bachelors and come heavily armed. I’m not going to be a political prisoner in the state of Oregon. It’s just that simple."

Disappearing quorum

The similar tactic of disappearing quorum (refusing to vote although physically present on the floor) was used by the minority to block votes in the United States House of Representatives until 1890. That year, SpeakerThomas Brackett Reed ordered that members who were present but abstaining would count in the quorum.