Characterization of aerobic and anaerobic vegetative growth of the food-borne pathogen Bacillus cereus F4430/73 strain

Abstract

The Gram-positive bacterium Bacillus cereus is a facultative anaerobe that is still poorly characterized metabolically. In this study, the aerobic vegetative growth and anaerobic vegetative growth of the food-borne pathogen B. cereus F4430/73 strain were compared with those of the genome-sequenced ATCC14579 strain using glucose and glycerol as fermentative and nonfermentative carbon sources, respectively. Uncontrolled batch cultures on several defined media showed that B. cereus strains had high amino acid or pyruvate requirements for anaerobic fermentative growth. In addition, growth performance was considerably improved by maintaining the pH of the culture medium near neutrality. Spectra of fermentation by-products were typically (per mole of glucose) 0.2-0.4 acetate, 1.1-1.4 L-lactate, 0.3-0.4 formate, and 0.05-0.2 ethanol with only traces of succinate, pyruvate, and 2,3-butanediol. These spectra were drastically changed in the presence of 20 mmol nitrate x L(-1), which stimulated anaerobic growth. During anaerobic and aerobic respiration, the persistent production of acetate and other by-products indicated overflow metabolisms. This was especially true in glucose-grown cells for which respiratory complex III made only a minor contribution to growth. Surprisingly, oxygen uptake rates linked to the cytochrome c and quinol branches of the respiratory chain were maintained at high levels in anaerobic, respiring, or fermenting cells. Growth and metabolic features of B. cereus F4430/73 are discussed using biochemical and genomic data.

Control of Enterotoxin Gene Expression in Bacillus cereus F4430/73 Involves the Redox-Sensitive ResDE Signal Transduction System

“…Impact of resDE and resE mutations on the glucose catabolism of B. cereus. As shown in Table 2, the spectra of glucose by-products are quantitatively the same as those found previously under low-and high-ORP anaerobiosis (55) and under full aerobiosis (41) in the case of the wild-type F4430/73 cells. Briefly, wild-type cells switched gradually from fully fermentative to fully respiratory metabolism as more oxygen become available, with acetate being the most persistent by-product.…”

“…In both bacteria, we identified genes or operons encoding NADH dehydrogenases (yumB, yjlD, yutJ, and yrkE), succinate dehydrogenase (sdhABC) potentially functioning as a fumarate reductase, complex III (qcrABC), proton-pumping terminal oxidases such as cytochrome aa3 quinol oxidase (qoxABCD) and cytochrome c oxidase (ctaDEF), and non-proton-pumping cytochrome bd quinol oxidases (cydAB). We also showed that both the cytochrome c and quinol branches of the respiratory chain coexist in B. cereus independently of oxygen availability (41). In the absence of O 2 or other external electron acceptor (such as nitrate), ATP synthesis occurs at the level of substrate phosphorylation and the demand for redox neutrality is met by electron transfer from reducing equivalents (such as NADH) to an internal electron acceptor (such as pyruvate or acetyl coenzyme A).…”

“…The most striking of these changes was in the mRNA profile of the three genes encoding putative L-lactate dehydrogenase and the upregulation of genes encoding pyruvate dehydrogenase (pdh), alcohol dehydrogenase (adhA), and acetate kinase (ackA). Lactate dehydrogenase is particularly important for B. cereus F4430/73 since lactate forms the bulk (70%) of the fermentation end products (41). The resE mutant seems to only partially compensate for the downregulation of ldhA through the induction of ldhB, since NADH-dependent lactate production is decreased (by 1.5-fold compared to the wild type).…”

“…Escherichia coli strains were propagated in Luria-Bertani medium. B. cereus F4430/73 wild-type (47) and mutants were grown in the synthetic MOD medium supplemented with 30 mM glucose as a carbon source (41,55). When required, antibiotics were used at the following concentrations: 50 g of ampicillin ml…”

ApoFnr Binds as a Monomer to Promoters Regulating the Expression of Enterotoxin Genes of Bacillus cereus

“…cereus will grow efficiently by anaerobic glucose fermentation in amino acid-rich media supplemented with glucose as the major source of carbon and energy (3,21,29,33,34). The ability of B. cereus to grow well under these conditions is controlled by both the two-component system ResDE (4) and the redox regulator Fnr (33,34).…”