Effect of CTXφ prophage deletion in cholera agent on expression of regulatory genes controlling virulence and biofilm formation

Abstract

This work represents the results of comparative analysis of the nucleotide sequences in the chromosomal region containing CTXφ prophage in isogenic toxigenic (Tox⁺) and nontoxigenic (Tox^–) strains of Vibrio cholerae biovar El Tor. It is shown that spontaneous mutants which have identical Tox^– phenotype are formed either owing to the precise elimination of CTX_φ prophage from the chromosome (deletion size is 6.9 kb) or owing to imprecise elimination with the additional loss of two other prophages (RS1φ and TLC_φ), which are adjacent to CTX_φ prophage (deletion size is 17.4 kb). It is revealed that, in the nontoxigenic mutants, CTX_φ deletion initiates simultaneous change in several phenotypic properties, which are associated with virulence or biofilm formation, such as colonizing ability, HA/P production, VPS, and motility. For the first time, it is stated that the cause of the pleiotropic effect of the CTX_φ deletion is a cascade decrease in the transcription levels of seven regulatory genes (toxR, aphA, tcpP, tcpH, toxT, vpsT, vpsR) which control virulence and biofilm formation processes in the cholera agent.