Comparative genomic analysis of Clostridium acetobutylicum for understanding the mutations contributing to enhanced butanol tolerance and production.

Clostridium acetobutylicum JB200 is a hyper butanol tolerant and producing strain obtained from asporogenic C. acetobutylicum ATCC 55025 through mutagenesis and adaptation in a fibrous bed bioreactor. The complete genomes of both strains were sequenced by the Illumina Hiseq2000 technology and assembled using SOAPdenovo approach. Compared to the genomic sequence of the type strain ATCC 824, 143 single nucleotide polymorphisms (SNPs) and 17 insertion/deletion variations (InDels) were identified in the genome of ATCC 55025. Twenty-nine mutations were in genes involved in sporulation, solventogenesis and stress response. Compared to ATCC 55025, there were seven additional point mutations in the chromosome of JB200. Among them, a single-base deletion in cac3319 encoding an orphan histidine kinase caused protein C-terminal truncation. Disruption of this gene in ATCC 55025 and ATCC 824 resulted in significantly elevated butanol tolerance and production. This study provides genome-level information for the better understanding of solventogenic C. acetobutylicum in several key aspects of cell physiology and metabolism, which could help further metabolic engineering of Clostridium for butanol production.