CytR Is a Global Positive Regulator of Competence, Type VI Secretion, and Chitinases in Vibrio cholerae
Panel A: V. cholerae C6706 is capable of natural transformation in LB medium lacking chitin if tfoX is constitutively expressed (TfoX*, bar 1) but not if tfoX is under control of its native promoter (TfoX+, bars 3 and 4). No transformants were detected in the absence of CytR (CytR-, bars 2 and 4). Transformation frequency is expressed as the number of kanamycin resistant cfu mL-1 divided by total cfu mL-1. The limit of detection (d.l.) is 1 x 10−8. Data are shown as mean ± standard deviation from three independent biological replicates. Panel B: Heat map of genes differentially regulated by CytR in the absence (TfoX+, column 1) or presence (TfoX*, column 2) of TfoX induction, and genes differentially regulated by TfoX in the absence (CytR-, column 3) or presence (CytR+, column 4) of a functional cytR gene. The majority of known competence genes are positively regulated by both TfoX and CytR and can be classified into four distinct regulatory classes (see text for details). CytR and TfoX positively regulate the three known T6SS gene clusters as well as four chitinase genes. CytR negatively regulates nucleoside uptake and catabolism genes in a TfoX-independent manner.