title: Alternative sigma factors SigF, SigE, and SigG are essential for sporulation in Clostridium botulinum ATCC 3502.
abstract: Clostridium botulinum produces heat-resistant endospores that may germinate and outgrow into neurotoxic cultures in foods. Sporulation is regulated by the transcription factor Spo0A and the alternative sigma factors SigF, SigE, SigG, and SigK in most spore formers studied to date. We constructed mutants of sigF, sigE, and sigG in C. botulinum ATCC 3502 and used quantitative reverse transcriptase PCR and electron microscopy to assess their expression of the sporulation pathway on transcriptional and morphological levels. In all three mutants the expression of spo0A was disrupted. The sigF and sigE mutants failed to induce sigG and sigK beyond exponential-phase levels and halted sporulation during asymmetric cell division. In the sigG mutant, peak transcription of sigE was delayed and sigK levels remained lower than that in the parent strain. The sigG mutant forespore was engulfed by the mother cell and possessed a spore coat but no peptidoglycan cortex. The findings suggest that SigF and SigE of C. botulinum ATCC 3502 are essential for early sporulation and late-stage induction of sigK, whereas SigG is essential for spore cortex formation but not for coat formation, as opposed to previous observations in B. subtilis sigG mutants. Our findings add to a growing body of evidence that regulation of sporulation in C. botulinum ATCC 3502, and among the clostridia, differs from the B. subtilis model.
authors.affiliation: Department of Food Hygiene and Environmental Health, Centre of Excellence in Microbial Food Safety Research, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
authors.forename: David G
authors.initials: DG
authors.lastname: Kirk
authors.affiliation: Department of Food Hygiene and Environmental Health, Centre of Excellence in Microbial Food Safety Research, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Department of Food Hygiene and Environmental Health, Centre of Excellence in Microbial Food Safety Research, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Korkeala
authors.affiliation: Department of Food Hygiene and Environmental Health, Centre of Excellence in Microbial Food Safety Research, Faculty of Veterinary Medicine, University of Helsinki, Helsinki, Finland miia.lindstrom@helsinki.fi.
authors.forename: Miia
authors.initials: M
authors.lastname: Lindström
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003014:Clostridium botulinum / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D013171:Spores, Bacterial / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C064971:FliA protein, Bacteria; D012808:Sigma Factor; C111259:sigE protein, Bacteria