Competence regulation by oxygen availability and by Nox is not related to specific adjustment of central metabolism in Streptococcus pneumoniae

In Streptococcus pneumoniae oxygen availability is a major determinant for competence development in exponentially growing cultures, NADH oxidase acti vity is required for optimal competence in cultures grown aerobically, The implication of oxidative metabolism and more specifically of Nor on central metabolism has been examined, Glycolytic flux throughout exponential growt h revealed homolactic fermentation with a lactate production/glucose utiliz ation ratio close to 2, whatever the aerobiosis level of the culture. Loss- of-function mutations in nor, which encodes NADH oxidase, did not change th is trait, Consistently, mRNA levels of glyceraldehyde-3-phosphate dehydroge nase, L-lactate dehydrogenase, pyruvate oxidase, and NADH oxidase remained comparable to wild-type levels, as did the specific activities of key enzym es which control central metabolism. Competence regulation by oxygen involv ing the NADH oxidase activity is not due to significant modification of car bon flux through glycolysis. Failure to obtain loss-of-function mutation in L-ldh, which encodes the L-lactate dehydrogenase, indicates its essential role in pneumococci whatever their growth status.