Genomic, Transcriptional, and Phenotypic Analysis of the Glucose Derepressed Clostridium beijerinckii Mutant Exhibiting Acid Crash Phenotype

Clostridium beijerinckii is a predominant solventogenic bacterium that has been used for the ABE fermentation. Various C. beijerinckii mutants have been constructed for desirable phenotypes. The C. beijerinckii mutant BA105 harboring a glucose derepression phenotype was previously isolated and demonstrated the enhanced amylolytic activity in the presence of glucose. Despite its potential use, BA105 has not been further characterized and utilized. Therefore, we investigated fermentation phenotypes of BA105 in this study. Under the typical batch fermentation conditions, BA105 consistently exhibited acid crash phenotype resulting in limited glucose uptake and cell growth. However, when the culture pH was maintained above 5.5, BA105 exhibited the increased glucose uptake and butanol production than did the wild-type. To further analyze BA105, we performed genome sequencing and RNA sequencing. Genome analysis identified two SNPs unique to BA105, in the upstream region of AbrB regulator (Cbei_4885) and the ROK family glucokinase (Cbei_4895) which are involved in catabolite repression and regulation of sugar metabolism. Transcriptional analysis of BA105 revealed significant differential expression of the genes associated with the PTS sugar transport system and acid production. This study improves understanding of the acid crash phenomenon and provides the genetic basis underlying the catabolite derepression phenotype of C. beijericnkii.