The growth of Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii subsp. bulgaricus) on lactose was altered upon aerating the cultures by agitation. Aeration caused the bacteria to enter early into stationary phase, thus reducing markedly the biomass production but without modifying the maximum growth rate. The early entry into stationary phase of aerated cultures was probably related to the accumulation of hydrogen peroxide in the medium. Indeed, the concentration of hydrogen peroxide in aerated cultures was two to three times higher than in unaerated ones. Also, a similar shift from exponential to stationary phase could be induced in unaerated cultures by adding increasing concentrations of hydrogen peroxide. A significant fraction of the hydrogen peroxide produced by L. delbrueckii subsp. bulgaricus originated from the reduction of molecular oxygen by NADH catalyzed by an NADH:H 2 O 2 oxidase. The specific activity of this NADH oxidase was the same in aerated and unaerated cultures, suggesting that the amount of this enzyme was not directly regulated by oxygen. Aeration did not change the homolactic character of lactose fermentation by L. delbrueckii subsp. bulgaricus and most of the NADH was reoxidized by lactate dehydrogenase with pyruvate. This indicated that NADH oxidase had no (or a very small) energetic role and could be involved in eliminating oxygen.Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii subsp. bulgaricus) is an important species of lactic acid bacteria currently used in the industrial production of fermented milk products. L. delbrueckii subsp. bulgaricus is an aerotolerant anaerobe that obtains most of its energy from homolactic fermentation (12). It does not require strict anaerobic growth conditions and tolerates the concentration of O 2 in air. Even though L. delbrueckii subsp. bulgaricus does not use O 2 in its energetic metabolism, it is likely that the presence of oxygen in its environment can influence its physiology. Indeed, some lactic acid bacteria possess oxidases that utilize molecular oxygen to oxidize substrates such as pyruvate (22) or NADH (2,5,8,16,(23)(24)(25). As these oxidation reactions cannot occur under anaerobic conditions, metabolism in the presence of oxygen cannot be identical to that in the absence of oxygen. Also, the activities of these oxidases can produce partially reduced oxygen species such as the superoxide radical (O 2 .Ϫ ), hydrogen peroxide (H 2 O 2 ), the hydroxyl radical (HO . ), and other peroxyl radicals or peroxides that will cause an oxidative stress in the cell. It is therefore expected that the presence of oxygen will induce a specific cellular response to such oxidative stress. In this work, a difference in the growth of L. delbrueckii subsp. bulgaricus in the presence and absence of oxygen was observed. It was also found that L. delbrueckii subsp. bulgaricus could reduce oxygen into hydrogen peroxide with an NADH oxidase, probably to eliminate the oxygen present. However, this detoxification of oxygen led to an overproducti...

Phosphatidylinositol (PI)1 and its phosphorylated derivatives regulate many biological processes, including cell proliferation, cell survival, differentiation, signal transduction, cytoskeleton organization, and membrane trafficking (reviewed in Ref. 1). Various chemical species can be generated by single, double, or triple phosphorylations at the inositol hydroxy groups at positions 3, 4, and 5. Their synthesis and cellular concentrations are regulated by specific lipid kinases and phosphatases. One of the major mechanisms by which PIs regulate cellular processes is by their capacity to serve as membrane signals to affect intracellular localizations of effector proteins.

The genes encoding the toxic determinants of Bacillus sphaericus have been expressed in a nontoxic and a toxic strain of Bacillus thuringiensis subsp. israelensis. In both cases, the B. sphaericus toxin proteins were produced at a high level during sporulation of B. thuringiensis and accumulated as crystalline structures. B. thuringiensis transformants expressing B. sphaericus and B. thuringiensis subsp. israelensis toxins did not show a significant enhancement of toxicity against Aedes aegypti, Anopheles stephensi, and Culex pipiens larvae.