Bacterial quorum sensing, cooperativity, and anticipation of stationary-phase stress

Abstract

Acyl-homoserine lactone-mediated quorum sensing (QS) regulates diverse activities in many species of Proteobacteria. QS-controlled genes commonly code for production of secreted or excreted public goods. The acyl-homoserine lactones are synthesized by members of the LuxI signal synthase family and are detected by cognate members of the LuxR family of transcriptional regulators. QS affords a means of population density-dependent gene regulation. Control of public goods via QS provides a fitness benefit. Another potential role for QS is to anticipate overcrowding. As population density increases and stationary phase approaches, QS might induce functions important for existence in stationary phase. Here we provide evidence that in three related species of the genus Burkholderia QS allows individuals to anticipate and survive stationary-phase stress. Survival requires QS-dependent activation of cellular enzymes required for production of excreted oxalate, which serves to counteract ammonia-mediated alkaline toxicity during stationary phase. Our findings provide an example of QS serving as a means to anticipate stationary phase or life at the carrying capacity of a population by activating the expression of cytoplasmic enzymes, altering cellular metabolism, and producing a shared resource or public good, oxalate.Burkholderia carrying capacity | glumae | pseudomallei | thailandensis | cell death A cyl-homoserine lactone (AHL)-mediated quorum sensing (QS) regulates diverse activities, including bioluminescence, biofilm formation, motility, and virulence factor formation, in many Proteobacteria (1-3). AHLs are synthesized most typically by members of the LuxI family signal synthases and detected by members of the LuxR family of transcriptional regulators (1-3). A large body of work has characterized the molecular mechanisms of bacterial QS; demonstrating the population-wide benefits that drive QS-mediated cooperative behavior has proven difficult, however. Cooperative activities benefit individuals within a group (4, 5).QS-controlled genes commonly code for the production of extracellular public goods that can be shared by all members of the group regardless of which members produce them. These extracellular products are often important for nutrient acquisition, interspecies competition, or virulence (6-8). In Pseudomonas aeruginosa, QS control of secreted proteases provides fitness benefits, because the proteases are produced only when they can be used efficiently (9). Other potential roles of QS in bacteria have been proposed, including the hypothesis that QS enables bacteria to anticipate population carrying capacity in a given environment. Anticipation of stationary phase might allow individuals to modify their physiology in preparation for survival at population carrying capacity.Here we address the question of whether QS is involved in anticipation of stationary-phase stress in three closely related bacteria: the rice pathogen Burkholderia glumae, the opportunistic human pathogen Burkholderia pseudomallei, and the...

Bacterial quorum sensing and metabolic slowing in a cooperative population

“…To explain why the other NTPs were also unbalanced, we estimated the expression levels of the phosphoribosylglycinamide synthetase D (purD) and carbamoyl phosphate synthase A (carA) genes involved in de novo purine and pyrimidine biosynthesis, respectively, as suggested by our earlier RNAseq data (11). The expression levels of both genes were higher in QS mutants than in the wild type (Fig.…”

“…In addition to the feedback inhibition circuits characteristic of many biochemical processes (8-10), we hypothesized that QS might control both glucose uptake and metabolic homeostasis of individual cells in crowded populations based upon earlier analyses of QS-dependent gene expression in Burkholderia glumae and the role of QS in regulating the respiration of Burkholderia thailandensis (11,12). The model organism used in this study, B. glumae, is an important agricultural pathogen due to its ability to cause rice panicle blight.…”

“…Based on a previous analysis of QS-dependent gene expression in B. glumae (11), we hypothesized that QS might affect glucose uptake in individual cells. To determine the effect of QS on glucose uptake, we chose ptsI (bglu_1g31820), one of two phosphoenolpyruvate-protein phosphotransferase genes and a representative gene in the multicomponent phosphoenolpyruvate-dependent sugar phosphotransferase system (PTS), based on previously published RNAseq results (11) and measured the expression levels in wild type (BGR1), the tofI mutant BGS2, and the qsmR mutant BGS9. Expression of ptsI was significantly higher in the QS mutants than the wild type (Fig.…”

Structural Insights into an Oxalate-producing Serine Hydrolase with an Unusual Oxyanion Hole and Additional Lyase Activity

“…Cloning and Purification of Wild-type Obc1 and Its Mutants-The gene for Obc1 from B. thailandensis (7,11) was amplified by colony PCR and cloned into a modified pET28b expression vector (Merck) containing a tobacco etch virus protease recognition sequence between the His 5 tag and multiple cloning site. The resulting plasmid containing N-terminal Histagged Obc1 was transformed into Escherichia coli BL21 (DE3) cells (Novagen).…”

“…In Burkholderia species, quorum sensing-mediated oxalogenesis is an indispensable cellular event for survival during the stationary growth phase (1,7). Oxalate is a highly acidic molecule that serves as a public good and plays a central role in maintaining pH homeostasis.…”