Interspecies communication is basically limited to species sharing the same system, although a limited crosstalk is possible between bacteria that use chemically similar AHLs [10�C12].A second quorum sensing system (QS-2, [13]) was discovered in V. harveyi [14]. This system is controlled by the LuxS protein that catalyzes http://www.selleckchem.com/products/Vorinostat-saha.html the production of (S)-4,5-dihydroxy-2,3-pentanedione (DPD). DPD is the direct precursor of a different autoinducer molecule (AI-2), (2S,4S)-2-methyl-2,3,3, 4-tetrahydroxytetrahydrofuryl borate (S-THMF-borate), a furanosyl borate diester [15] (Figure 1). In Vibrio spp., the AI-2 signal is detected by the two-component sensor kinase LuxPQ and is ultimately linked to the same transduction pathway used by the QS-1 sketched above and a third quorum sensing system, which is based on signal molecule (S)-3-hydroxytridecan-4-one (CAI-1) in Vibrio cholerae [16] and Vibrio harveyi [17].
All three signals are conveyed through the central signal relay protein LuxU and the terminal response regulator LuxO, the latter controlling gene expression together with sigma factor ��54 [18], whereby the strengths of the different autoinducer signals are not equivalent and vary from species to species [19,20]. In bacterial orders other than the Vibrionaceae, the task of detecting a different form of the DPD-derived AI-2 signal, (2R,4S)-2-methyl-2,3,3,4-tetrahydroxytetrahydrofuran (R-THMF), is carried out by an ABC-transporter, the Lsr-receptor complex. Orthologs of this protein are prevalent mainly in Enterobacteriaceae [21,22], Pasteurellaceae and Bacillaceae, but were not detected in Vibrionaceae [23].
The presence of LuxS has been reported in several subgroups of the bacterial kingdom such as Actinobacteria, Bacilli, Bacteroidetes, Deinococci and Beta-, Gamma-, and Epsilonproteobacteria. Conversely, LuxS has not been described in Archaea nor in Eukarya [24,25]. The pervasive nature of the luxS gene, embracing both Gram-negative and Gram-positive bacteria, Entinostat led to the presumption that QS-2 may be the foundation of a bacterial Esperanto; that is to say, a universal language spoken and understood by various bacterial species [26]. Unfortunately, this assumption has often neglected a crucial function of LuxS in bacterial cells. This protein has an enzymatic role in the activated methyl cycle (AMC) [25], which accounts for the regeneration of the major methyl donor S-adenosyl-L-methionine (SAM) and the recycling of methionine by detoxification of S-adenosyl-L-homocysteine (SAH) in the cell (Figure 1). This omission www.selleckchem.com/products/AZD2281(Olaparib).html has repeatedly led to the misinterpretation as QS of metabolic effects in in vitro mutational experiments and to the incorrect interpretation of in silico genomic data (see Section 5) [23].