Comparison of Transcriptomes and Sporulation of Two Clostridium botulinum A1 Strains

Abstract

subtype A1 strains are one of the major causes of human botulism. Two of the genome-sequenced subtype A1 strains, Hall A and ATCC 3502, exhibit unique phenotypes in sporulation and botulinum neurotoxin (BoNT) production. Hall A, a hyper toxin producer used in BoNT/A production for medicinal and research purposes, is known to be deficient in sporulation, while ATCC 3502 is a laboratory strain capable of forming spores and producing a modest level of BoNT. Microarray-based transcriptomes were compared between these strains to identify key molecules contributing to these different phenotypes. Expression analysis showed that Hall A strain exhibited an increased expression level of the toxin cluster genes, which correlates to its hyper toxin production. Hall A also displayed a lower expression level of the sporulation initiation master regulator, Spo0A, and the forespore-specific Sigma F and Sigma G, which correlates to its poor sporulation phenotypes. In addition, Hall A showed a lowered expression level of CBO1120, a histidine sensor kinase that has been shown to activate sporulation by phosphorylating Spo0A. Further analysis of the sequences of CBO1120 showed an A to G base substitution at nucleotide position 661 resulting in a mutation of E221K. The differential expression of spo0A and CBO1120, as well as the critical point mutation identified in CBO1120, may imply that spo0A is not only poorly expressed in Hall A, its phosphorylation activation by the sensor histidine kinase may also be impaired. Overall, our genomic sequence and microarray analyses have brought insights into the genetic and physiological differences between the two Type A1 strains. The results may lead to further understanding of the sporulation process in