Quorum sensing system

Since the initial discovery of quorum sensing regulation of bacteriocin synthesis in LAB, numerous systems have been described both among Class I and Class II bacteriocins. An overview of the best-characterized PPs of the various three-component systems among Class II bacteriocins is presented in Tables 1 and 2. It should be emphasized that not all Class II bacteriocins are regulated through such a quorum sensing system and several bacteriocins seem to be constitutively produced. 

Table 3 Peptide pheromone (PP) lactone signaling quorum sensing systems. The processed peptides shaded in yellow have to be post-translationally modified to become active...

Smith, R. S. and Iglewski, B. H. (2003). P. aeruginosa quorum sensing systems and virulence. Curr. Opin. Microbiol, 6, 56-60. 

Figure 15 Quorum sensing system involved in the regulation of nisin A. After translated from nisA prepropeptide of nisin is modified, processed, and secreted via NisB, NisC, NisT, and NisP. The mature nisin A binds to NisK and triggers the phosphorelay to NisR. The phosphorylated NisR induces transcriptions of two operons nisABTCIP and nisFEG encoding immunity protein complex.

Figure 25 The relation of Lux and Ain quorum sensing systems in Vibrio fischeri for bioluminescence.

Pseudomonas aeruginosa is an opportunistic pathogen and infects especially immunocompromised patients.266-270 Many clinical isolates of P. aeruginosa are identified not only from the inside of the body but also from the biofilm formed on indwelling catheter or medical devices. Quorum sensing system of P. aeruginosa has been extensively studied and several kinds of systems have been reported.2 1-292... 

The relationship between these two quorum sensing systems, Las and Rhl, is very interesting. C4-HSL does not activate LasR, but 3-oxo-C12-LasR complex showed a low level activation of RhlR. The Las system... 

The third system is also related to both Las and Rhl systems, but not to the AHL-mediated one. The signal molecule is 2-heptyl-3-hydroxy-4-quinolone (PQS). PQS quorum sensing system is described in Section 4.07.5.3.2. 

AI-2-mediated quorum sensing system in Serratia species was also found and is described in Section 4.07.5.3.1. 

Chromobacterium violaceum is commonly found in soil and water and produces a purple pigment named violacein (Figure 32), which is water insoluble and has an antibacterial activity. Violacein production is regulated by Cvil—CviR quorum sensing system with C6-HSL in C. violaceum,316... 

The autoinducer of the third quorum sensing system in P. aeruginosa is PQS. (Figure 36) PQS is involved in lasB expression, and RhlR is required for PQS activity. The structure of PQS is similar to that of antimicrobial quinolones, but PQS shows no antimicrobial activity. PQS is converted from 2-heptyl-4(lH)-quinolone (HHQ) by PqsH, which is activated by 3-oxo-Cl2-HSL—LasR. PQS regulates the expression of elastase, rhamnolipid, pyocyanin, and LecA. As PQS regulates LasB expression and the synthesis of PQS is regulated by LasR and... 

RhlR, PQS-mediated regulation is not independent but linked to both las and rhl quorum sensing systems.326-329 Until now, PQS quorum sensing has been reported only in P. aeruginosa, but PQS gene homologues were found in Burkholderia species. PQS-mediated quorum sensing may be extended to other bacterial species in future. 

Although the basic AHL quorum sensing system only consists of two proteins—LuxI and LuxR—a variety of proteins modulates it. These proteins include the AiiA AHL lactonase of Bacillus thuringiensis, which inactivates AHL by hydrolysing... 

The list discussed here is by no means complete (for a comprehensive list, see Reference (34)), and it is reasonable to expect that even more bacterial quorum sensing systems await discovery, especially when considering the vast amounts of microbial diversity made available by metagenomics projects. 

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