AUTHOR=Smith Veronika , Josefsen Malin , Lindbäck Toril , Hegna Ida K. , Finke Sarah , Tourasse Nicolas J. , Nielsen-LeRoux Christina , Økstad Ole Andreas , Fagerlund Annette 

TITLE=MogR Is a Ubiquitous Transcriptional Repressor Affecting Motility, Biofilm Formation and Virulence in Bacillus thuringiensis

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.610650

DOI=10.3389/fmicb.2020.610650

ISSN=1664-302X

ABSTRACT=<p>Flagellar motility is considered an important virulence factor in different pathogenic bacteria. In <italic>Listeria monocytogenes</italic> the transcriptional repressor MogR regulates motility in a temperature-dependent manner, directly repressing flagellar- and chemotaxis genes. The only other bacteria known to carry a <italic>mogR</italic> homolog are members of the <italic>Bacillus cereus</italic> group, which includes motile species such as <italic>B. cereus</italic> and <italic>Bacillus thuringiensis</italic> as well as the non-motile species <italic>Bacillus anthracis</italic>, <italic>Bacillus mycoides</italic> and <italic>Bacillus pseudomycoides.</italic> Furthermore, the main motility locus in <italic>B. cereus</italic> group bacteria, carrying the genes for flagellar synthesis, appears to be more closely related to <italic>L. monocytogenes</italic> than to <italic>Bacillus subtilis</italic>, which belongs to a separate phylogenetic group of Bacilli and does not carry a <italic>mogR</italic> ortholog. Here, we show that in <italic>B. thuringiensis</italic>, MogR overexpression results in non-motile 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 biofilm lifestyle. Accordingly, phenotypic assays showed that MogR also affects cytotoxicity and biofilm formation in <italic>B. thuringiensis</italic>. Overexpression of a MogR variant mutated in two amino acids within the putative DNA binding domain restored phenotypes to those of an empty vector control. In accordance, introduction of these mutations resulted in complete loss in MogR binding to its candidate flagellar locus target site <italic>in vitro</italic>. In contrast to <italic>L. monocytogenes</italic>, MogR appears to be regulated in a growth-phase dependent and temperature-independent manner in <italic>B. thuringiensis</italic> 407. Interestingly, <italic>mogR</italic> was found to be conserved also in non-motile <italic>B. cereus</italic> group species such as <italic>B. mycoides</italic> and <italic>B. pseudomycoides</italic>, which both carry major gene deletions in the flagellar motility locus and where in <italic>B. pseudomycoides mogR</italic> is the only gene retained. Furthermore, <italic>mogR</italic> is expressed in non-motile <italic>B. anthracis.</italic> Altogether this provides indications of an expanded set of functions for MogR in <italic>B. cereus</italic> group species, beyond motility regulation. In conclusion, MogR constitutes a novel <italic>B. thuringiensis</italic> 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.</p>