Identification and properties of type I‐signal peptidases of Bacillus amyloliquefaciens

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Abstract
The use of Bacillus amyloliquefaciens for enzyme production and its exceptional high protein export capacity initiated this study where the presence and function of multiple type I signal peptidase isoforms was investigated. In addition to type I signal peptidases SipS(ba) [Meijer, W.J.J., de Jong, A., Bea, G., Wisman, A., Tjalsma, H., Venema, G., Bron, S. & van Dijl, J.M. (1995) Mol. Microbiol.17, 621–631] and SipT(ba) [Hoang, V. & Hofemeister, J. (1995) Biochim. Biophys. Acta1269, 64–68] which were previously identified, here we present evidence for two other Sip‐like genes in B. amyloliquefaciens. Same map positions as well as sequence motifs verified that these genes encode homologues of Bacillus subtilis SipV and SipW. SipU‐encoding DNA was not found in B. amyloliquefaciens. SipW‐encoding DNA was also found for other Bacillus strains representing different phylogenetic groups, but not for Bacillus stearothermophilus and Thermoactinomyces vulgaris. The absence of these genes, however, could have been overlooked due to sequence diversity. Sequence alignments of 23 known Sip‐like proteins from Bacillus origin indicated further branching of the P‐group signal peptidases into clusters represented by B. subtilis SipV, SipS‐SipT‐SipU and B. anthracis Sip3‐Sip5 proteins, respectively. Each B. amyloliquefaciens sip(ba) gene was expressed in an Escherichia coli LepBts mutant and tested for genetic complementation of the temperature sensitive (TS) phenotype as well as pre‐OmpA processing. Although SipS(ba) as well as SipT(ba) efficiently restored processing of pre‐OmpA in E. coli, only SipS(ba) supported growth at TS conditions, indicating functional diversity. Changed properties of the sip(ba) gene disruption mutants, including cell autolysis, motility, sporulation, and nuclease activities, seemed to correlate with specificities and/or localization of B. amyloliquefaciens SipS, SipT and SipV isoforms.

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