Phylogeny and functional conservation of sigma(E) in endospore-forming bacteria

Conservation of the sporulation processes between Bacillus spp. and Clostri dium spp. was investigated through evolutionary and complementation analyse s of sigma(E). Alignment of partial predicted sigma(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 pr omoter utilization (M124, E119 and N120) and strand opening (C117) are cons erved among all these species. Phylogenetic analyses of various sigma facto r sequences from endospore-forming bacteria revealed that homologues of sig ma(E), sigma(K) and sigma(G) clustered together regardless of genus, sugges ting a common origin of sporulation sigma factors. The functional equivalen ce between Clostridium acetobutylicum sigma(E) and Bacillus subtilis sigma( E) was investigated by complementing a non-polar B. subtilis sigma(E) null mutant with the spollG operon from either B. subtilis (spollG(Bs)) or C. ac etobutylicum (spollG(Ca). Single-copy integration of spollG(Bs) into the am yE locus of the sigma(E) null mutant completely restored the wild-type spor ulation phenotype, while spollG(Ca) only partially restored sporulation. Ma ximal expression of spollG(Ca)-lacZ occurred approximately 12 h later than maximal expression of spollG(Bs)-lacZ. Differences in temporal expression p atterns for spollG(Ca) and spollG(Bs) in the B. subtilis background may at least partially explain the observed sporulation complementation phenotypes . This study suggests a common phylogenetic ancestor for sigma(E) in Bacill us spp. and Clostridium spp., although regulation of sigma(E) expression ma y differ in these two genera.