Cytochromec₅₅₁and the CytochromecMaturation Pathway Affect Virulence Gene Expression in Bacillus cereus ATCC 14579

Abstract

Loss of the cytochrome c maturation system in Bacillus cereus results in increased transcription of the major enterotoxin genes nhe, hbl, and cytK and the virulence regulator plcR. Increased virulence factor production occurs at 37°C under aerobic conditions, similar to previous findings in Bacillus anthracis. Unlike B. anthracis, much of the increased virulence gene expression can be attributed to loss of only c 551 , one of the two small c-type cytochromes. Additional virulence factor expression occurs with loss of resBC, encoding cytochrome c maturation proteins, independently of the presence of the c-type cytochrome genes. Hemolytic activity of strains missing either cccB or resBC is increased relative to that in the parental strain, while sporulation efficiency is unaffected in the mutants. Increased virulence gene expression in the ⌬cccB and ⌬resBC mutants occurs only in the presence of an intact plcR gene, indicating that this process is PlcR dependent. These findings suggest a new mode of regulation of B. cereus virulence and reveal intriguing similarities and differences in virulence regulation between B. cereus and B. anthracis.

Intraclade Variability in Toxin Production and Cytotoxicity of Bacillus cereus Group Type Strains and Dairy-Associated Isolates

“…Future studies that examine the regulation of Hbl, Nhe, and cytotoxin K toxins among isolates belonging to different clades will be key to understanding the contributions of these toxins to in vitro cytotoxicity and in vivo virulence. Overall, the observed heterogeneity of cytotoxicity among isolates in multiple B. cereus clades without a clear association between genetic and phenotypic data suggests the importance of regulatory mechanisms, such as activity of the virulence gene regulator PlcR ( 62 ), or other regulatory elements which have previously been associated with virulence factor expression ( 63 , 64 ). Alternatively, the observed cytotoxicity characterized here could result from the production of unidentified toxins in isolates where discrepant results between the detection of genes and proteins and cytotoxicity were observed.…”

Typing and evaluating heat resistance of Bacillus cereus sensu stricto isolated from the processing environment of powdered infant formula

“…This toxin, a small and highly stable cyclic peptide, may be produced by B. cereus s. s. strains harboring the ces gene (Kumari and Sarkar, 2016). They are difficult to inactivate by standard food processing approaches or human gastric digestion once cereulide has formed in contaminated foods or associated ingredients (Ehling-Schulz et al, 2004;Han et al, 2015). Sequence type 26 and ST144, which have been associated with ces carriage, have been increasingly isolated from infant foods in recent years (Zhang et al, 2016;Yang et al, 2017).…”

Heme A Synthase Deficiency Affects the Ability of Bacillus cereus to Adapt to a Nutrient-Limited Environment

“…B. cereus cytochrome caa3 is made up of four proteins (CtaCDEF), with Cu A and a cytochrome c domain in subunit II (CtaC). This protein may form a supercomplex with the cytochrome bc complex (QcrABC) and cytochrome c 550 (CccA) or cytochrome c 551 [4] in the membrane, as reported in B. subtilis [5]. Cytochrome caa3 is one of the two heme-copper terminal oxidases in the branched B. cereus aerobic respiratory chain [6,7] (Figure 1).…”