Importance of spore mutants for fed‐batch and continuous fermentation of Bacillus subtilis

To alleviate plasmid instability and to prolong the production phase of subtilisin, integrable plasmid and spore mutants are used. Compared with batch‐type shake flask cultures, spore mutants' ability to produce subtilisin can be well pronounced in fed‐batch and continuous cultures. Hence, the two culture methods make it possible to identify the peculiar characteristics of the spore mutants unobtainable in batch culture. Spore mutants can enhance subtilisin productivity and prolong subtilisin production time in fed‐batch culture as well as enable us to use very low dilution rates (<0.1 h⁻¹) without losing productivity in continuous culture, thereby improving the conversion yield of the nitrogen source. At 0.05 h⁻¹ the spollG mutant of Bacillus subtilis DB104 (Δnpr Δapr) (Em^r) spollG (Bim^r):: pMK101 (Cm^r) showed a subtilisin yield about ten times higher than that from wild‐type DB104 (Δnpr Δapr)::pMK101 (Cm^r). © 1995 John Wiley & Sons, Inc.