An aerobic endospore-forming bacillus (NVH 391-98^T) was isolated during a severe food poisoning outbreak in France in 1998, and four other similar strains have since been isolated, also mostly from food poisoning cases. Based on 16S rRNA gene sequence similarity, these strains were shown to belong to the Bacillus cereus Group (over 97 % similarity with the current Group species) and phylogenetic distance from other validly described species of the genus Bacillus was less than 95 %. Based on 16S rRNA gene sequence similarity and MLST data, these novel strains were shown to form a robust and well-separated cluster in the B. cereus Group, and constituted the most distant cluster from species of this Group. Major fatty acids (iso-C_15 : 0, C_16 : 0, iso-C_17 : 0, anteiso-C_15 : 0, iso-C_16 : 0, iso-C_13 : 0) supported the affiliation of these strains to the genus Bacillus , and more specifically to the B. cereus Group. NVH 391-98^T taxon was more specifically characterized by an abundance of iso-C_15 : 0 and low amounts of iso-C_13 : 0 compared with other members of the B. cereus Group. Genome similarity together with DNA–DNA hybridization values and physiological and biochemical tests made it possible to genotypically and phenotypically differentiate NVH 391-98^T taxon from the six current B. cereus Group species. NVH 391-98^T therefore represents a novel species, for which the name Bacillus cytotoxicus sp. nov. is proposed, with the type strain NVH 391-98^T ( = DSM 22905^T = CIP 110041^T)_.

Cell-free supernatants from growingBacillus cereusstrain ATCC 10987 induced luminescence in aPhotorhabdus luminescensΔluxSmutant, indicating the production of functional autoinducer 2 (AI-2). The exogenous addition of in vitro synthesized AI-2 had an inhibitory effect on biofilm formation byB. cereusand promoted release of the cells from a preformed biofilm.

Biofilm formation by 102 Bacillus cereus and B. thuringiensis strains was determined. Strains isolated from soil or involved in digestive tract infections were efficient biofilm formers, whereas strains isolated from other diseases were poor biofilm formers. Cell surface hydrophobicity, the presence of an S layer, and adhesion to epithelial cells were also examined.

YrzC has previously been identified as a repressor controllingytmIexpression via its regulation of YtlI activator synthesis inBacillus subtilis.We identified YrzC as a master regulator of sulfur metabolism. Gene expression profiles ofB. subtilisΔyrzCmutant and wild-type strains grown in minimal medium with sulfate as the sole sulfur source were compared. In the mutant, increased expression was observed for 24 genes previously identified as repressed in the presence of sulfate. Since several genes involved in the pathways leading to cysteine formation were found, we propose to rename YrzC CymR, for “cysteine metabolism repressor.” A CymR-dependent binding to the promoter region of theytlI,ssuB,tcyP,yrrT,yxeK,cysK, orydbMgene was demonstrated using gel shift experiments. A potential CymR target site, TAAWNCN₂ANTWNAN₃ATMGGAATTW, was found in the promoter region of these genes. In a DNase footprint experiment, the protected region in theytlIpromoter region contained this consensus sequence. Partial deletion or introduction of point mutations in this sequence confirmed its involvement inytlI,yrrT, andyxeKregulation. The addition ofO-acetylserine in gel shift experiments prevented CymR-dependent binding to DNA for all of the targets characterized. Transcriptome analysis of a ΔcymRmutant and the wild-type strain also brought out significant changes in the expression level of a large set of genes related to stress response or to transition toward anaerobiosis.

Bacillus subtilis can use methionine as the sole sulfur source, indicating an efficient conversion of methionine to cysteine. To characterize this pathway, the enzymatic activities of CysK, YrhA and YrhB purified in Escherichia coli were tested. Both CysK and YrhA have an O -acetylserine-thiol-lyase activity, but YrhA was 75-fold less active than CysK. An atypical cystathionine β-synthase activity using O -acetylserine and homocysteine as substrates was observed for YrhA but not for CysK. The YrhB protein had both cystathionine lyase and homocysteine γ-lyase activities in vitro. Due to their activity, we propose that YrhA and YrhB should be renamed MccA and MccB for methionine-to-cysteine conversion. Mutants inactivated for cysK or yrhB grew similarly to the wild-type strain in the presence of methionine. In contrast, the growth of an Δ yrhA mutant or a luxS mutant, inactivated for the S -ribosyl-homocysteinase step of the S -adenosylmethionine recycling pathway, was strongly reduced with methionine, whereas a Δ yrhA ΔcysK or cysE mutant did not grow at all under the same conditions. The yrhB and yrhA genes form an operon together with yrrT , mtnN , and yrhC . The expression of the yrrT operon was repressed in the presence of sulfate or cysteine. Both purified CysK and CymR, the global repressor of cysteine metabolism, were required to observe the formation of a protein-DNA complex with the yrrT promoter region in gel-shift experiments. The addition of O -acetyl-serine prevented the formation of this protein-DNA complex.