Vibrio alginolyticus EPGS strain aphB ChIP-SEQ

In Vibrios, AphB is essential to activate virulence cascades by sensing low pH and anaerobiosis signals. However, its regulon remains largely unknown. Here, AphB is found as a key virulence regulator in V. alginolyticus, a pathogen for marine animals and humans. Chromatin immunoprecipitation followed by high-throughput DNA sequencing enabled the detection of 20 loci in the V. alginolyticus genome that contain AphB-binding peaks. An AphB-specific binding consensus was confirmed by electrophoretic mobility shift assays (EMSA), and the regulation of genes near such binding sites was demonstrated using quantitative real-time PCR analysis. AphB binds directly to its own promoter and positively controls its own expression at later growth stages. AphB also activates the expression of the exotoxin Asp by binding directly to the promoter regions of asp and the master quorum-sensing (QS) regulator luxR. DNase I footprinting analysis uncovered the distinct AphB-binding sites (BBS) in these promoters. Furthermore, BBS in the luxR promoter region overlaps with that of LuxR binding site I, which mediates the positive control of the luxR promoter activity by AphB. This study provides new insights into the AphB regulon and reveals the mechanisms underlying the AphB regulation of physiological adaptation and QS-controlled virulence in V. alginolyticus.