CytR Is a Global Positive Regulator of Competence, Type VI Secretion, and Chitinases in Vibrio cholerae
V. cholerae C6706 derivatives with native alleles of tfoX, cytR and qstR (not constitutively expressed, denoted by +), alleles of tfoX or qstR made constitutive by replacing the chromosomal native promoter with a ptac promoter (indicated by *), or containing in-frame deletions of tfoX, cytR, hapR and qstR (-), were analyzed for expression of bioluminescence from plasmid-encoded lux transcriptional reporter fusions. Expression profiles are shown for the transcriptional regulator qstR (Panel A) and for a member of each regulatory class: class I, comEA (Panel B) class II, pilM (Panel C) class III, pilF, (Panel D), and class IV, pilT (Panel E). All strains are deleted for luxO and are therefore constitutive for HapR expression (*) when the hapR gene is present. Bioluminescence is represented as relative light production per OD600 (RLU) and data shown are mean values ± standard deviation from three biological replicates of one representative experiment of three. Data are shown as mean values ± standard deviation. ‡ indicates a p-value < 0.01, † indicates a p-value <0.05. N.S. denotes not significant, calculated using a two-tailed Student’s t-test. In Panels A to E, bars 2–5 are compared to bar 1; in Panels A and B, bars 7–9 are compared to bar 6. Panel F: A TfoX* CytR+ HapR* QstR* strain is transformable in LB in the absence of chitin induction, but an isogenic strain carrying a qstR deletion was poorly transformable. The hapR deletion strain was partially restored for transformation by constitutive expression of QstR (*), but strains deleted for cytR or tfoX were not restored for competence by the QstR* allele. The limit of detection is 1 x 10−8 cfu. mL-1 (d.l.).