PMID:21325136

Citation	Rutherford, ST, van Kessel, JC, Shao, Y and Bassler, BL (2011) AphA and LuxR/HapR reciprocally control quorum sensing in vibrios. Genes Dev. 25:397-408
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.
Links	PubMed PMC3042162 Online version:10.1101/gad.2015011
Keywords	Bacterial Proteins/genetics; Bacterial Proteins/metabolism; Bacterial Proteins/physiology; Base Sequence; Gene Expression Profiling; Gene Expression Regulation, Bacterial; Microarray Analysis; Models, Biological; Molecular Sequence Data; Quorum Sensing/genetics; Quorum Sensing/physiology; Repressor Proteins/genetics; Repressor Proteins/metabolism; Repressor Proteins/physiology; Sequence Homology, Nucleic Acid; Trans-Activators/genetics; Trans-Activators/metabolism; Trans-Activators/physiology; Vibrio/genetics; Vibrio/metabolism; Vibrio/physiology
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
VIBHA:A6AR68		GO:0010944: negative regulation of transcription by competitive promoter binding	IMP: Inferred from Mutant Phenotype:	P	AphA is shown to negatively regulate the expression of genes qrr2, qrr3 and qrr4 in figure 2B when an aphA deletion causes an increase in expression of qrr2,3 and 4. It also shows negative regulation of qrr4 in figure 2A when an aphA interrupted mutant resulted in an increase in qrr4 expression. Further in the paper, figure 3 shows that AphA binds directly to the qrr4 promoter negatively regulating transcription.	complete

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