Effect of spo0A, sigE, sigG, and sigK disruption on butanol production and spore formation in Clostridium saccharoperbutylacetonicum strain N1-4 (ATCC13564).

Clostridium saccharoperbutylacetonicum strain N1-4 (ATCC13564) is a butanol-producing strain suitable for application to butanol production from cellulosic materials by co-culture with cellulolytic and thermophilic species, such as Hungateiclostridium thermocellum (synonym: Clostridium thermocellum). The optimal temperature for butanol production by strain N1-4 is 30 °C, and the strain is sensitive to a high culture temperature of 37 °C. Given that spore formation is observed at high frequency when strain N1-4 is cultivated at 37 °C, we assumed in a previous study that the initiation of sporulation is related to a decrease in butanol production. Therefore, to investigate the relationship between butanol production and spore formation, we generated strain N1-4 isolates in which genes related to spore formation were disrupted. The sporulation-related gene disruptants of spo0A, sigE, sigG, and sigK lost the ability to produce heat-resistant spores, irrespective of the culture temperature. Among the gene disruptants produced, only the spo0A disruptant lost butanol-producing ability when cultivated at 30 °C. Interestingly, the sigE disruptant maintained butanol productivity similar to that observed at 30 °C, even when cultivated at 37 °C. In addition, the sigE disruptant successfully produced butanol from Avicel cellulose by co-culture with H. thermocellum at a fermentation temperature of 37 °C.