Abstract
BackgroundMost extracellular virulence factors produced by Bacillus cereus are regulated by the pleiotropic transcriptional activator PlcR. Among strains belonging to the B. cereus group, the plcR gene is always located in the vicinity of genes encoding the YvfTU two-component system. The putative role of YvfTU in the expression of the PlcR regulon was therefore investigated.ResultsExpression of the plcR gene was monitored using a transcriptional fusion with a lacZ reporter gene in a yvfTU mutant and in its B. cereus ATCC 14579 parental strain. Two hours after the onset of the stationary phase, a stage at which the PlcR regulon is highly expressed, the plcR expression in the yvfTU mutant was only 50% of that of its parental strain. In addition to the reduced plcR expression in the yvfTU mutant, a few members of the PlcR regulon showed a differential expression, as revealed by transcriptomic and proteomic analyses. The virulence of the yvfTU mutant in a Galleria mellonella insect model was slightly lower than that of the parental strain.ConclusionThe YvfTU two-component system is not required for the expression of most of the virulence factors belonging to the PlcR regulon. However, YvfTU is involved in expression of plcR, a major regulator of virulence in B. cereus.
Highlights
Most extracellular virulence factors produced by Bacillus cereus are regulated by the pleiotropic transcriptional activator PlcR
Identification of genes encoding a two-component systems (TCS) in the vicinity of the plcR locus among the B. cereus group Genes encoding a TCS (BC5352 and BC5353) were located between 5,263 kb and 5,265 kb on the minus strand of the B. cereus ATCC 14579 chromosome (Fig. 1A)
The BC5353 and BC5352 genes studied here have been annotated as yocF and yocG in the B. cereus strain ATCC 14579 [15]
Summary
Most extracellular virulence factors produced by Bacillus cereus are regulated by the pleiotropic transcriptional activator PlcR. B. cereus is mostly observed as a causative agent of food poisoning This species belongs to the B. cereus group that includes the closely related species Bacillus anthracis, Bacillus thuringiensis, Bacillus weihenstephanensis, Bacillus mycoides and Bacillus pseudomycoides [1,2]. Expression of most of these virulence factors is controlled by the pleiotropic transcriptional activator PlcR [3,4,5] This global regulator contributes to B. cereus virulence in mice, in insects [6] and to rabbit endophthalmitis [7]. The PlcR-PapR active complex binds a DNA target site, designated as the PlcR box, activating transcription of the PlcR regulon genes [3,10]
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