MogR is a ubiquitous transcriptional repressor affecting motility, biofilm formation and virulence in the Bacillus cereus group

Flagellar motility is considered an important virulence factor in a range of different pathogenic bacteria. In Listeria monocytogenes the transcriptional repressor MogR regulates motility in a temperature-dependent manner by directly repressing flagellar- and chemotaxis genes. The only other bacteria known to carry a mogR homolog are members of the Bacillus cereus group, which includes both motile and non-motile species. Furthermore, the motility locus in B. cereus group bacteria appears to be more closely related to L. monocytogenes than to Bacillus subtilis. In this study we show that in Bacillus thuringiensis, overexpression of MogR results in non-motile host cells devoid of flagella. Global gene expression profiling showed that 110 genes were differentially regulated by MogR overexpression, including flagellar motility genes, but also genes associated with virulence, stress response and a biofilm lifestyle. Accordingly, phenotypic assays showed that MogR also affects cytotoxicity and biofilm formation in B. thuringiensis. Overexpression of a MogR variant mutated in two key amino acids within the putative DNA binding domain restored phenotypes to those of a wild type empty vector control strain. In line with this, the introduction of these mutations resulted in complete loss in the ability of MogR to bind to its putative target site within the flagellar motility locus in vitro. In contrast to L. monocytogenes, MogR appears to be regulated in a growth-phase dependent and temperature-independent manner in B. thuringiensis 407. Interestingly, mogR was found to be conserved also in non-motile B. cereus group species with highly reduced motility loci, such as Bacillus mycoides and Bacillus pseudomycoides, and is expressed in non-motile Bacillus anthracis, providing further indications of an expanded and unexpected set of functions for MogR in B. cereus group species, in addition to motility regulation. In conclusion, MogR constitutes a novel B. cereus group pleiotropic transcriptional regulator, acting as a repressor of motility genes, and affecting the expression of a variety of additional genes involved in biofilm formation and virulence.