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Bacillus cereus causes gastrointestinal diseases and local and systemic infections elicited by the depsipeptide cereulide, enterotoxins, phospholipases, cytolysins and proteases. The PlcR-PapR quorum sensing system activates the expression of several virulence factors, whereas the Spo0A-AbrB regulatory circuit partially controls the plasmid-borne cereulide synthetase (ces) operon. Here, we show that CodY, a nutrient-responsive regulator of Gram-positive bacteria, has a profound effect on both regulatory systems, which have been assumed to operate independently of each other. Deletion of codY resulted in downregulation of virulence genes belonging to the PlcR regulon and a concomitant upregulation of the ces genes. CodY was found to be a repressor of the ces operon, but did not interact with the promoter regions of PlcR-dependent virulence genes in vitro, suggesting an indirect regulation of the latter. Furthermore, CodY binds to the promoter of the immune inhibitor metalloprotease InhA1, demonstrating that CodY directly links B. cereus metabolism to virulence. In vivo studies using a Galleria mellonella infection model, showed that the codY mutant was substantially attenuated, highlighting the importance of CodY as a key regulator of pathogenicity. Our results demonstrate that CodY profoundly modulates the virulence of B. cereus, possibly controlling the development of pathogenic traits in suitable host environments.

Water kefir is a home made fermented beverage based on a sucrose solution with fruit extracts. The inoculum of such fermentations consists of macroscopic granula containing lactic and acetic acid bacteria, and yeasts, which are embedded in an exopolysaccharide (EPS) matrix. In this work, a strain of Lactobacillus hilgardii producing large amounts of the granule-forming dextran could be isolated. The glycosyltransferans (Gtf) commonly called glucansucrase responsible for the production of this dextran was purified from L. hilgardii . Characteristic enzyme kinetic data were obtained. Optimum activity was observed between pH 4.3 and 4.6 and temperatures between 40 °C and 45 °C. A Michaelis–Menten kinetic could be fit to the experimental data and a K M of 0.0385 M was calculated. The corresponding gtf gene was identified and characterized. It encodes a 1448 amino acid protein with higher homologies to Gtfs of Lactobacillus parabuchneri , Lactobacillus sakei and Lactobacillus fermentum followed by lower homologies to Lactobacillus reuteri Gtfs. By knockout experiments the role of this gene in granule dextran production was demonstrated.