Bacillus cereus F4430/73 produced the highest levels of hemolysin BL (HBL) when grown under anaerobiosis in MOD medium. Anaerobic cells grown in a chemostat at low specific growth rate (0.1-0.2 h(-1)) expressed up to sevenfold more HBL than did cells held at a faster growth rate. At 0.2 h(-1), the presence of 90 mM glucose resulted in inhibition of HBL production. Glucose was found to repress HBL induction at the mRNA level, indicating the potential involvement of catabolite repression in the regulation of HBL. Based on these data, it is suggested that growth rate could be an effector of catabolite regulation of HBL.

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Aims:The physiological consequences of low external oxidoreduction potential in Leuconostoc mesenteroides were investigated. Methods and Results: Leuconostoc mesenteroides was grown under two initial oxidoreduction potential conditions (E h7 : +200 mV and )400 mV) using nitrogen and hydrogen as reducing agents. Growth was affected by E h7 ; the lag phase increased from 1 h at an initial E h7 of +200 mV to 6 h at an initial E h7 of )400 mV; the maximum specific growth rate at )400 mV was 68% of the one observed at +200 mV. The NADH/NAD + ratio and (NADH + NAD + ) pool were independent of the external E h7 . Conclusions: This study shows that changing the external oxidoreduction potential from +200 to )400 mV has a strong effect on the Leuc. mesenteroides physiology. The constancy of the maximum carbon and energetic fluxes (q glu , q ATP ) under the two E h7 conditions accompanied by the decrease of Y X/S and Y ATP suggested the existence of an uncoupling phenomenon, namely that some catabolized glucose and hence ATP was not associated with biomass production. Significance and Impact of the Study: This paper demonstrates the usefulness of taking into account, the effect of the oxidoreduction potential on the growth of Leuc. mesenteroides in the fermentation process.

International audienceSugar citrate cometabolism in Leuconostoc mesenteroides. Bacteria from the genus Leuconostoc play roles in the dairy industry. The most important functions of this bacteria are their ability to produce CO$_2$ and flavour compounds through lactose heterofermentation and citrate utilization. Although the biotechnological role of the citrate metabolism is very important and widely appreciated, little is known about the genetic properties of Leuconostoc spp. In our laboratory, we cloned the genes responsible for citrate metabolism (clyR mae citCDEFGOP cluster), for D-lactate dehydrogenase (ldhD) and for phosphotransacetylase (pta). In addition we have planned to construct new vectors and we have tried to improve a method to introduce recombinant DNA molecules into Leuconostoc as well. Characterization of the plasmid involved in this study is still in progress. The nucleotide sequence analysis of p22R revealed the presence of C5 cytosine methylase gene typical of type II restriction/modification system. The low transformation efficiency of some strains of Leuconostoc may be due to the presence of that plasmid. The construction of the defective strain for restriction activity could be very useful to genetic manipulations of Leuconostoc in the future.Les Leuconostoc sont utilisés dans l'industrie laitière pour leur capacité à produire du CO$_2$ et des composés d'arôme (diacétyle) grâce au cométabolisme du citrate et du lactose. Les gènes du métabolisme du citrate (clyR mae citCDEFGOP), de la lactate déshydrogénase et de la phosphotransacétylase ont été clonés dans notre laboratoire. Ces différents gènes semblent de bons candidats pour des expériences d'ingénierie métabolique. C'est pourquoi un des aspects de notre travail consiste à développer et améliorer les méthodes de transfert et de manipulation d'ADN de Leuconostoc. En parallèle, la caractérisation du plasmide de 10 kb de L. mesenteroides p22R est en cours. L'analyse de la séquence partielle a révélé la présence d'un gène codant pour une C5 cytosine méthylase. Cette méthylase est typique des systèmes de restriction/modification de type II. Il est possible que la présence de ce plasmide soit responsable de la faible efficacité du transfert de l'ADN chez les Leuconostoc. La construction d'une souche R$^-$M$^+$ devrait faciliter les manipulations ultérieures des bactéries du genre Leuconostoc