Metabolic profiles and aprE expression in anaerobic cultures of Bacillus subtilis using nitrate as terminal electron acceptor

Cultures using nitrate as the terminal electron acceptor were conducted in Schaeffer's medium to evaluate the growth performance and metabolic profile s of Bacillus subtilis, and its potential to express the aprE (subtilisin) gene under anoxic conditions. Nitrate was converted to ammonia through nitr ite reduction; and different product profiles were observed during the grow th phase when nitrate was added at various concentrations (4-24 mM) to Scha effer's medium containing glucose (4 g l(-1)). If nitrate was not limiting, then acetic acid and acetoin were accumulated, suggesting a limitation of reduced cofactors but, if nitrate became limiting, then lactic acid and but anediol were accumulated, suggesting an excess of reduced cofactors. Due to a strong lysis at the onset of the end of the growth phase, sporulation fr equency and aprE expression were negligible in anaerobic batch cultures. Fe d-batch fermentation allowed the development of a stationary phase through a continuous supply of glucose and nitrate. In this case, sporulation frequ ency was almost null, but interestingly aprE expression was similar to that found in aerobic cultures.