AphA and LuxR/HapR reciprocally control quorum sensing in vibrios

Abstract

Bacteria cycle between periods when they perform individual behaviors and periods when they perform group behaviors. These transitions are controlled by a cell-cell communication process called quorum sensing, in which extracellular signal molecules, called autoinducers (AIs), are released, accumulate, and are synchronously detected by a group of bacteria. AI detection results in community-wide changes in gene expression, enabling bacteria to collectively execute behaviors such as bioluminescence, biofilm formation, and virulence factor production. In this study, we show that the transcription factor AphA is a master regulator of quorum sensing that operates at low cell density (LCD) in Vibrio harveyi and Vibrio cholerae. In contrast, LuxR (V. harveyi)/HapR (V. cholerae) is the master regulator that operates at high cell density (HCD). At LCD, redundant small noncoding RNAs (sRNAs) activate production of AphA, and AphA and the sRNAs repress production of LuxR/HapR. Conversely, at HCD, LuxR/HapR represses aphA. This network architecture ensures maximal AphA production at LCD and maximal LuxR/HapR production at HCD. Microarray analyses reveal that 300 genes are regulated by AphA at LCD in V. harveyi, a subset of which is also controlled by LuxR. We propose that reciprocal gradients of AphA and LuxR/ HapR establish the quorum-sensing LCD and HCD gene expression patterns, respectively.

A quorum-sensing inhibitor blocks Pseudomonas aeruginosa virulence and biofilm formation

“…Total RNA was prepared using the RNeasy Midi Kit (Qiagen). cDNA was synthesized and normalized as previously reported (35). cDNA was hybridized using the Gene Expression Hybridization Kit (Agilent) to a custom microarray (Agilent design ID 43307), which was designed using the Agilent eArray tool with two probes for most genes.…”

Cyclo(valine–valine) inhibits Vibrio cholerae virulence gene expression

“…Although N16961 was hapR-negative, it was possible that genes upstream of hapR in the QS system could affect aphA expression in response to cVV (reviewed by Ng & Bassler, 2009). LuxO has been shown to activate expression of the QS regulated small (s)RNAs (Qrrs), which function with the Hfq chaperone to positively regulate AphA production at low cell density (Rutherford et al, 2011;Shao & Bassler, 2012). Therefore, one possible mechanism by which cVV could affect aphA expression is downregulation of luxO, Qrr's or hfq.…”

Comprehensive analysis reveals how single nucleotides contribute to noncoding RNA function in bacterial quorum sensing

“…LuxO∼P activates transcription of genes encoding five homologous noncoding small RNAs (sRNAs) called the quorum-regulatory RNAs 1-5, or Qrr1-5 (15,16). The Qrr sRNAs, in conjunction with the chaperone Hfq, activate translation of the LCD master regulator called AphA and destabilize the mRNA encoding LuxR, the high-cell density (HCD) master regulator (16,17). AphA controls genes that underpin individual behaviors (17,18).…”

“…The Qrr sRNAs, in conjunction with the chaperone Hfq, activate translation of the LCD master regulator called AphA and destabilize the mRNA encoding LuxR, the high-cell density (HCD) master regulator (16,17). AphA controls genes that underpin individual behaviors (17,18). At HCD, AI binding converts the receptors to phosphatases, resulting in dephosphorylation and inactivation of LuxO, and cessation of qrr expression (13,15).…”

“…This event terminates Qrr activation of AphA translation, and luxR mRNA is stabilized, leading to LuxR production. LuxR controls the expression of genes that underlie collective processes (17)(18)(19)(20). The Qrr sRNAs feed back to repress luxO, and they repress or activate 17 additional mRNA targets (21).…”