Quadruple Quorum-Sensing Inputs Control Vibrio cholerae Virulence and Maintain System Robustness

Abstract

Bacteria use quorum sensing (QS) for cell-cell communication to carry out group behaviors. This intercellular signaling process relies on cell density-dependent production and detection of chemical signals called autoinducers (AIs). Vibrio cholerae, the causative agent of cholera, detects two AIs, CAI-1 and AI-2, with two histidine kinases, CqsS and LuxQ, respectively, to control biofilm formation and virulence factor production. At low cell density, these two signal receptors function in parallel to activate the key regulator LuxO, which is essential for virulence of this pathogen. At high cell density, binding of AIs to their respective receptors leads to deactivation of LuxO and repression of virulence factor production. However, mutants lacking CqsS and LuxQ maintain a normal LuxO activation level and remain virulent, suggesting that LuxO is activated by additional, unidentified signaling pathways. Here we show that two other histidine kinases, CqsR (formerly known as VC1831) and VpsS, act upstream in the central QS circuit of V. cholerae to activate LuxO. V. cholerae strains expressing any one of these four receptors are QS proficient and capable of colonizing animal hosts. In contrast, mutants lacking all four receptors are phenotypically identical to LuxO-defective mutants. Importantly, these four functionally redundant receptors act together to prevent premature induction of a QS response caused by signal perturbations. We suggest that the V. cholerae QS circuit is composed of quadruple sensory inputs and has evolved to be refractory to sporadic AI level perturbations.

Antisocial luxO Mutants Provide a Stationary-Phase Survival Advantage in Vibrio fischeri ES114

“…LuxO is part of a PS network conserved throughout the Vibrionaceae that has been well studied over the last 3 decades. Other luxO* mutants have been reported in the Vibrionaceae, isolated both from natural populations and during laboratory experiments (54,(57)(58)(59)(60)(61). Recently, phenotypic discrepancies between two ⌬luxU mutants of V. cholerae were discovered to be due to one strain harboring a previously undetected luxO* mutation (58,59), which is reminiscent of our own discovery of spontaneous luxO* causing phenotypes we initially attributed to defined transposon insertions.…”

“…Each diamond represents the log RCI in one hatchling. and those from previous studies in other vibrios aligned to the V. fischeri sequence (filled triangles) (53,54,57,58,60). Rectangles represent LuxO domains, including the regulatory (gray), AAA ϩ /RpoN interaction (hatched), and DNA-binding (white) domains.…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…V. fischeri harbors three distinct QS systems (i.e., AinS/AinR, LuxI/LuxR, and LuxS/LuxPQ); however, only the AinS/AinR system is involved in the modulation of the initial steps of surface colonization, and only the AinS/AinR and LuxS/LuxPQ systems are involved in the modulation of subsequent biofilm development (418,419). V. cholerae harbors four distinct QS systems (i.e., CqsA/CqsS, LuxS/ LuxPQ, CqsR, and VpsS), and they all participate in the modulation of surface colonization and biofilm formation (420). Functional redundancy of the four QS receptors is employed by V. cholerae to prevent premature induction of a QS response that may be caused by signal perturbations (420).…”

“…V. cholerae harbors four distinct QS systems (i.e., CqsA/CqsS, LuxS/ LuxPQ, CqsR, and VpsS), and they all participate in the modulation of surface colonization and biofilm formation (420). Functional redundancy of the four QS receptors is employed by V. cholerae to prevent premature induction of a QS response that may be caused by signal perturbations (420). The QS systems in V. fischeri assist in establishing a symbiotic relationship between the bacterium and its host, Euprymna scolopes, while the QS systems in V. cholerae contribute to making this bacterium a deadly pathogen to humans.…”

Quorum Sensing Gene Regulation by LuxR/HapR Master Regulators in Vibrios

“…1), LuxN, LuxPQ, and CqsS, and each binds a specific autoinducer (autoinducer 1 [AI-1], AI-2, and cholera autoinducer 1 [CAI-1], respectively) (41). V. cholerae has four autoinducer receptors that feed into the same circuit to regulate HapR, one of which is unlike canonical Vibrio receptors in that it is not membrane bound (11)(12)(13). A new autoinducer-receptor pair was identified in V. cholerae; binding of the autoinducer 3,5-dimethylpyrazin-2-ol (DPO) is required for dimerization and function of the cytosolic transcription factor VqmA, which indirectly inhibits biofilm formation (51).…”