Lactate Dehydrogenase A Promotes Communication between Carbohydrate Catabolism and Virulence in Bacillus cereus.

Sabrina Laouami (1) , Kahina Messaoudi (1) , François Alberto (1) , Thierry Clavel (1) , Catherine Duport (1)

1 SQPOV - Sécurité et Qualité des Produits d'Origine Végétale

The diarrheal potential of a Bacillus cereus strain is essentially dictated by the amount of secreted nonhe-molytic enterotoxin (Nhe). Expression of genes encoding Nhe is regulated by several factors, including the metabolic state of the cells. To identify metabolic sensors that could promote communication between central metabolism and nhe expression, we compared four strains of the B. cereus group in terms of metabolic and nhe expression capacities. We performed growth performance measurements, metabolite analysis, and mRNA measurements of strains F4430/73, F4810/72, F837/76, and PA cultured under anoxic and fully oxic conditions. The results showed that expression levels of nhe and ldhA, which encodes lactate dehydrogenase A (LdhA), were correlated in both aerobically and anaerobically grown cells. We examined the role of LdhA in the F4430/73 strain by constructing an ldhA mutant. The ldhA mutation was more deleterious to anaerobically grown cells than to aerobically grown cells, causing growth limitation and strong deregulation of key fermentative genes. More importantly, the ldhA mutation downregulated enterotoxin gene expression under both anaerobiosis and aerobiosis, with a more pronounced effect under anaerobiosis. Therefore, LdhA was found to exert a major control on both fermentative growth and enterotoxin expression, and it is concluded that there is a direct link between fermentative metabolism and virulence in B. cereus. The data presented also provide evidence that LdhA-dependent regulation of enterotoxin gene expression is oxygen independent. This study is the first report to describe a role of a fermentative enzyme in virulence in B. cereus. Bacillus cereus strains express various putative virulence genes, including genes encoding hemolysins, various entero-toxins, phospholipases, metalloproteases, collagenases, and other proteins (7, 38). The contribution of these putative vir-ulence factors to the pathogenicity of B. cereus strains has not been fully elucidated. However, the amount of secreted non-hemolytic enterotoxin (Nhe) appeared to essentially dictate B. cereus-associated cytotoxic activity (29). Nhe is a three-component enterotoxin encoded by the PlcR-regulated nheABC operon (nhe) (1, 16, 26). In in vitro culture, nhe transcription is responsive to a number of cues linked to carbohydrate catab-olism, including carbon source concentration, carbon source type, extracellular oxidoreduction potential, and growth phase (10, 28, 31, 42), which suggests that there are mechanisms to promote communication between carbohydrate catabolism and the nhe regulatory network. Carbohydrates such as glucose are catabolized primarily through the glycolytic pathway and to a lesser extent through the pentose phosphate pathway in growing B. cereus cells (42). Glycolysis produces two molecules of pyruvate per molecule of glucose consumed and in the process reduces two molecules of NAD ϩ to NADH. The cat

Mots clés: FOOD SAFETY; CYTOTOXICITY; FOOD MICROBIOLOGY; RT-PCR

Mots clés: CONTAMINATION

Domaines: Sciences du Vivant [q-bio]

Sabrina Laouami, Kahina Messaoudi, François Alberto, Thierry Clavel, Catherine Duport. Lactate Dehydrogenase A Promotes Communication between Carbohydrate Catabolism and Virulence in Bacillus cereus.. International Journal of Systematic Bacteriology, 2011, 193 (7), pp.1757-1766. ⟨10.1128/JB.00024-11⟩. ⟨hal-01330279⟩