Interspecies quorum sensing is a type of

quorum sensing In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...

in which bacteria send and receive signals to other species besides their own. This is accomplished by the secretion of signaling molecules which trigger a response in nearby bacteria at high enough concentrations. Once the molecule hits a certain concentration it triggers the

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

of certain genes such as

virulence factors Virulence factors (preferably known as pathogenicity factors or effectors in plant science) are cellular structures, molecules and regulatory systems that enable microbial pathogens (bacteria, viruses, fungi, and protozoa) to achieve the following ...

. It has been discovered that bacteria can not only interact via quorum sensing with members of their own species but that there is a kind of universal molecule that allows them to gather information about other species as well. This universal molecule is called autoinducer 2 or AI-2. AI-2 was first discovered in the light producing system of the bacteria ''

Vibrio harveyi ''Vibrio harveyi'' is a Gram-negative, bioluminescent, marine bacterium in the genus ''Vibrio''. ''V. harveyi'' is rod-shaped, motile (via polar flagella), facultatively anaerobic, halophilic, and competent for both fermentative and respiratory ...

''. The pathway that induces ''Vibrio harveyi''

luminescence Luminescence is spontaneous emission of light by a substance not resulting from heat; or "cold light". It is thus a form of cold-body radiation. It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a cryst ...

is controlled by two parallel pathways. The first pathway uses a typical AI-1 homoserine lactone signaling molecule. However the bacteria were also found to recognize a second auto inducer AI-2. Scientist also found that ''V. harveyi'' luminescence could be induced by 75 other bacterial species AI-2 molecules. This discovery led to the proposal of AI-2 as a universal form of communication between bacteria species. In addition to information about cell densities AI-2 can provide information on the growth phase and prosperity of cells in a population. It has a greater ability to store information than other quorum sensing molecules because its production is tied to cell growth. The production of AI-2 peaks in late log phase for many bacteria. The structure of AI-2 was discovered recently to be a fused 2-member ring with

boron Boron is a chemical element with the symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the ''boron group'' it has th ...

bridging the gap between the

diester In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides are ...

s. The enzyme LuxS is responsible for AI-2 synthesis. The gene encoding for LuxS has been detected in 35 of the 89 bacterial genomes sequenced and in all of the bacteria the gene had little variation. In every bacterium found so far that produces the AI-2 signaling molecule the LuxS gene was also found. There are three enzymes that make DPD ( 4,5-dihydroxy 2,3 pentanedione) which is the substrate LuxS uses to make AI-2. The pathway for synthesizing AI-2 was found to be identical in ''V. harveyi'', ''

E. coli ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

'', ''

Salmonella typhimurium ''Salmonella enterica'' subsp. ''enterica'' is a subspecies of ''Salmonella enterica'', the rod-shaped, flagellated, aerobic, Gram-negative bacterium. Many of the pathogenic serovars of the ''S. enterica'' species are in this subspecies, includi ...

'', '' V. cholerae'', and ''

Enterococcus faecalis ''Enterococcus faecalis'' – formerly classified as part of the group D ''Streptococcus'' system – is a Gram-positive, commensal bacterium inhabiting the gastrointestinal tracts of humans. Like other species in the genus ''Enterococcus'', ''E ...

'' providing further evidence that this molecule may be a universal signal among bacteria. ''Shigella flexneri'' use AI-2 to mediate

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ca ...

. The major virulence factor in ''Shigella'' is the

plasmid A plasmid is a small, extrachromosomal DNA molecule within a cell that is physically separated from chromosomal DNA and can replicate independently. They are most commonly found as small circular, double-stranded DNA molecules in bacteria; how ...

vir B. The AI-2 signaling pathway was shown to be responsible for the observed peak of vir B. Although it was determined that AI-2 is not crucial for virulence that it does increase the expression of the plasmid. AI-2 also regulates the virulence of Enteroinvasive and Enterohemoragic E.coli. It is likely the high concentrations of AI-2 produced by normal

gut flora Gut microbiota, gut microbiome, or gut flora, are the microorganisms, including bacteria, archaea, fungi, and viruses that live in the digestive tracts of animals. The gastrointestinal metagenome is the aggregate of all the genomes of the gut mi ...

effect the production of AI-2 in ''Shigella'' and its subsequent virulence. AI-2 is required for the

biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...

formation in ''P. ginivalis'' and ''S. gordonii''. ''S. gordonii'' is a major cause of

dental plaque Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found bet ...

and its adherence is essential for many other pathogenic bacteria to also adhere to teeth. ''P. ginivalis'' causes

periodontal disease Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...

. If neither bacteria possess a functional copy of the LuxS gene they cannot form a biofilm. However, if either one of the bacteria has the LuxS gene they can form biofilms suggesting again this molecule is used for communication between unrelated species. Other bacterial uses for AI-2 *''

Clostridium perfringens ''Clostridium perfringens'' (formerly known as ''C. welchii'', or ''Bacillus welchii'') is a Gram-positive, rod-shaped, anaerobic, spore-forming pathogenic bacterium of the genus '' Clostridium''. ''C. perfringens'' is ever-present in nature an ...

'' – regulates toxin production *''P. luminescence'' – controls the timing of

antibiotics An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention o ...

*''

Vibrio cholerae ''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...

'' – used in the pathogenic cascade Since the LuxS enzyme is not present in

eukaryotes Eukaryotes () are organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the three domains of life. Bacte ...

it is a good potential target for antibiotics. Also AI-2 signaling seems to control many virulence factors in bacteria so blocking this signal could lead to new ways to control bacterial infections such as cholera. Since the AI-2 molecule seems to be involved in the virulence cascade if we could block the uptake of AI-2 then we could potentially stop the virulence cascade.

Fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

also communicate with one another. Quorum-sensing molecules (QSMs) from fungi include

farnesol Farnesol is a natural 15-carbon organic compound which is an acyclic sesquiterpene alcohol. Under standard conditions, it is a colorless liquid. It is hydrophobic, and thus insoluble in water, but miscible with oils. Farnesol is produced from 5- ...

tyrosol Tyrosol is an organic compound with the formula . Classified as a phenylethanoid, i.e. a derivative of phenethyl alcohol, It is found in a variety of natural sources. The compound is colorless solid. The principal source in the human diet is ol ...

, phenylethanol, and

tryptophol Tryptophol is an aromatic alcohol that induces sleep in humans. It is found in wine as a secondary product of ethanol fermentation. It was first described by Felix Ehrlich in 1912. It is also produced by the trypanosomal parasite in sleeping sic ...

. QSMs have been studied in ''Candida albicans'', ''C. dubliniensis'', ''Aspergillus niger'', ''A. nidulans'', and ''Fusarium graminearum''. QSMs can include morphogenesis, germination, apotopsis, pathogenicity, and biofilm structures.

References

{{DEFAULTSORT:Interspecies Quorum Sensing Bacteriology

See also

References