Quorum sensing in thermophiles: prevalence of autoinducer-2 system

Abstract Background Quorum sensing is a mechanism of cell to cell communication that requires the production and detection of signaling molecules called autoinducers. Although mesophilic bacteria is known to utilize this for synchronization of physiological processes such as bioluminescence, virulence, biofilm formation, motility and cell competency through signaling molecules (acyl homoserine lactones, AI-1; oligopeptides, peptide based system and furanosyl borate diester, AI-2), the phenomenon of quorum sensing in thermophiles is largely unknown. Results In this study, proteomes of 106 thermophilic eubacteria and 21 thermophilic archaea have been investigated for the above three major quorum sensing systems to find the existence of quorum sensing in these thermophiles as there are evidences for the formation of biofilms in hot environments. Our investigation demonstrated that AI-1 system is absent in thermophiles. Further, complete peptide based two component systems for quorum sensing was also not found in any thermophile however the traces for the presence of response regulators for peptide based system were found in some of them. BLASTp search using LuxS (AI-2 synthase) protein sequence of Escherichia coli str. K-12 substr. MG1655 and autoinducer-2 receptors (LuxP of Vibrio harveyi, LsrB of E. coli str. K-12 substr. MG1655 and RbsB of Aggregatibacter actinomycetemcomitans) as queries revealed that 17 thermophilic bacteria from phyla Deinococcus- Thermus and Firmicutes possess complete AI-2 system (LuxS and LsrB and/or RbsB). Out of 106 thermophilic eubacteria 18 from phyla Deinococcus- Thermus, Proteobacteria and Firmicutes have only LuxS that might function as AI-2 synthesizing protein whereas, 16 are having only LsrB and/or RbsB which may function as AI-2 receptor in biofilms. Conclusions We anticipate that thermophilic bacteria may use elements of LsrB and RbsB operon for AI-2 signal transduction and they may use quorum sensing for purposes like biofilm formation. Nevertheless, thermophiles in which no known quorum sensing system was found may use some unknown mechanisms as the mode of communication. Further information regarding quorum sensing will be explored to develop strategies to disrupt the biofilms of thermophiles

RESPONSE SURFACE METHODOLOGY FOR THE OPTIMIZED PRODUCTION OF AN ALKALOPHILIC LACCASE FROM GAMMA-PROTEOBACTERIUM JB

Gamma-proteobacterium JB, an alkali-tolerant soil isolate, produced laccase (8X103 nkat/L) in M162 medium. The optimization of process conditions (pH, incubation time, agitation, and CuSO4 concentration) for laccase production during submerged fermentation was carried out using response surface methodology (RSM) based on a central composite design (CCD). Maximum laccase production achieved was 7.4 X 104 nkat/L at pH 8.0, 210 rpm, 100 µM of CuSO4 after 60 h of incubation. This design of experiment methodology increased laccase production by 9.3 fold over the control. Experimental findings were in close agreement with the model predictions

Additional file 15 of Quorum sensing in thermophiles: prevalence of autoinducer-2 system

STRING analysis of LuxS protein of Caminibacter mediatlanticus. (PDF 90 kb

Ellagic Acid Derivatives from <em>Terminalia chebula</em> Retz. Downregulate the Expression of Quorum Sensing Genes to Attenuate <em>Pseudomonas aeruginosa</em> PAO1 Virulence

<div><h3>Background</h3><p>Burgeoning antibiotic resistance in <em>Pseudomonas aeruginosa</em> has necessitated the development of anti pathogenic agents that can quench acylhomoserine lactone (AHL) mediated QS with least risk of resistance. This study explores the anti quorum sensing potential of <em>T. chebula</em> Retz. and identification of probable compounds(s) showing anti QS activity and the mechanism of attenuation of <em>P. aeruginosa</em> PAO1 virulence factors.</p> <h3>Methods and Results</h3><p>Methanol extract of <em>T. chebula</em> Retz. fruit showed anti QS activity using <em>Agrobacterium tumefaciens</em> A136. Bioactive fraction (F7), obtained by fractionation of methanol extract using Sephadex LH20, showed significant reduction (p<0.001) in QS regulated production of extracellular virulence factors in <em>P. aeruginosa</em> PAO1. Biofilm formation and alginate were significantly (p<0.05) reduced with enhanced (20%) susceptibility to tobramycin. Real Time PCR of F7 treated <em>P. aeruginosa</em> showed down regulation of autoinducer synthase (<em>lasI</em> and <em>rhlI</em>) and their cognate receptor (<em>lasR</em> and <em>rhlR</em>) genes by 89, 90, 90 and 93%, respectively. Electrospray Ionization Mass Spectrometry also showed 90 and 64% reduction in the production of 3-oxo-C₁₂HSL and C₄HSL after treatment. Decrease in AHLs as one of the mechanisms of quorum quenching by F7 was supported by the reversal of inhibited swarming motility in F7-treated <em>P. aeruginosa</em> PAO1 on addition of C₄HSL. F7 also showed antagonistic activity against 3-oxo-C₁₂HSL-dependent QS in <em>E. coli</em> bioreporter. <em>C. elegans</em> fed on F7-treated <em>P. aeruginosa</em> showed enhanced survival with LT50 increasing from 24 to 72 h. LC-ESI-MS of F7 revealed the presence of ellagic acid derivatives responsible for anti QS activity in <em>T. chebula</em> extract.</p> <h3>Conclusions</h3><p>This is the first report on anti QS activity of <em>T. chebula</em> fruit linked to EADs which down regulate the expression of <em>lasIR</em> and <em>rhlIR</em> genes with concomitant decrease in AHLs in <em>P. aeruginosa</em> PAO1 causing attenuation of its virulence factors and enhanced sensitivity of its biofilm towards tobramycin.</p> </div

N-acyl homoserine lactone mediated interspecies interactions between <i>A. baumannii</i> and <i>P. aeruginosa</i>

<div><p> <i>Acinetobacter baumannii</i> and <i>Pseudomonas aeruginosa</i> are pathogens capable of colonizing the same infection sites and employing N-acyl homoserine lactone (AHL) based quorum-sensing systems to co-ordinate biofilm formation. Hence, the effect of <i>P. aeruginosa</i> AHLs on biofilm formation by <i>A. baumannii</i> and <i>vice versa</i> were investigated using the biofilm impaired quorum sensing mutants, <i>A. baumannii</i> M2 (<i>aba</i>I::Km) and <i>P. aeruginosa</i> PAO-JP2. Complementing the mutants with heterologous, extracted and pure AHLs increased biofilm mass significantly. The surface area coverage and biovolume also increased significantly as observed by confocal scanning laser microscopy which corroborated scanning electron microscope analysis. Autoinducer synthase gene promoters of <i>A. baumannii</i>, P_<i>aba</i>I-<i>lac</i>Z, and <i>P. aeruginosa</i>, P_<i>las</i>I-<i>lacZ</i>, were induced (<i>p</i> < 0.05) by heterologous AHLs. Growth of <i>A. baumannii</i> was not inhibited by pyocyanin of <i>P. aeruginosa</i> which may allow their co-existence and interaction in the clinical setting, thereby affecting the severity of combined infections and therapeutic measures to control them.</p> </div

Additional file 9: of Quorum sensing in thermophiles: prevalence of autoinducer-2 system

Multiple sequence alignment of SAH hydrolase from thermophilic and mesophilic eubacteria by MultAlin. High conservation among SAH hydrolases has been observed. (PDF 274 kb