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Phylogeny and functional conservation of ^E in endospore-forming bacteria

Food Science Department, Cornell University, Ithaca, NY 14853, USA¹

Author for correspondence: Kathryn J. Boor. Tel: +1 607 255 3111. Fax: +1 607 254 4868. e-mail: kjb4{at}cornell.edu

Conservation of the sporulation processes between Bacillus spp. and Clostridium spp. was investigated through evolutionary and complementation analyses of ^E. Alignment of partial predicted ^E amino acid sequences from three Bacillus spp., Paenibacillus polymyxa and five Clostridium spp. revealed that amino acid residues previously reported to be involved in promoter utilization (M124, E119 and N120) and strand opening (C117) are conserved among all these species. Phylogenetic analyses of various sigma factor sequences from endospore-forming bacteria revealed that homologues of ^E, ^K and ^G clustered together regardless of genus, suggesting a common origin of sporulation sigma factors. The functional equivalence between Clostridium acetobutylicum ^E and Bacillus subtilis ^E was investigated by complementing a non-polar B. subtilis ^E null mutant with the spoIIG operon from either B. subtilis (spoIIG^Bs) or C. acetobutylicum (spoIIG^Ca). Single-copy integration of spoIIG^Bs into the amyE locus of the ^E null mutant completely restored the wild-type sporulation phenotype, while spoIIG^Ca only partially restored sporulation. Maximal expression of spoIIG^Ca–lacZ occurred approximately 12 h later than maximal expression of spoIIG^Bs–lacZ. Differences in temporal expression patterns for spoIIG^Ca and spoIIG^Bs in the B. subtilis background may at least partially explain the observed sporulation complementation phenotypes. This study suggests a common phylogenetic ancestor for ^E in Bacillus spp. and Clostridium spp., although regulation of ^E expression may differ in these two genera.

Keywords: sigma factors, sporulation, sigma E, Bacillus spp., Clostridium spp

The GenBank accession numbers for the sequences determined in this work are AF225461–AF225466.

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