J. Espinosa-de-los-monteros et al., Metabolic profiles and aprE expression in anaerobic cultures of Bacillus subtilis using nitrate as terminal electron acceptor, APPL MICR B, 57(3), 2001, pp. 379-384
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.