Description:
<jats:p>The use of <jats:italic>Bacillus amyloliquefaciens</jats:italic> 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(<jats:italic>ba</jats:italic>) [Meijer, W.J.J., de Jong, A., Bea, G., Wisman, A., Tjalsma, H., Venema, G., Bron, S. & van Dijl, J.M. (1995) <jats:italic>Mol. Microbiol.</jats:italic><jats:bold>17</jats:bold>, 621–631] and SipT(<jats:italic>ba</jats:italic>) [Hoang, V. & Hofemeister, J. (1995) <jats:italic>Biochim. Biophys. Acta</jats:italic><jats:bold>1269</jats:bold>, 64–68] which were previously identified, here we present evidence for two other Sip‐like genes in <jats:italic>B. amyloliquefaciens.</jats:italic> Same map positions as well as sequence motifs verified that these genes encode homologues of <jats:italic>Bacillus subtilis</jats:italic> SipV and SipW. SipU‐encoding DNA was not found in <jats:italic>B. amyloliquefaciens</jats:italic>. SipW‐encoding DNA was also found for other <jats:italic>Bacillus</jats:italic> strains representing different phylogenetic groups, but not for <jats:italic>Bacillus stearothermophilus</jats:italic> and <jats:italic>Thermoactinomyces vulgaris</jats:italic>. The absence of these genes, however, could have been overlooked due to sequence diversity. Sequence alignments of 23 known Sip‐like proteins from <jats:italic>Bacillus</jats:italic> origin indicated further branching of the P‐group signal peptidases into clusters represented by <jats:italic>B. subtilis</jats:italic> SipV, SipS‐SipT‐SipU and <jats:italic>B. anthracis</jats:italic> Sip3‐Sip5 proteins, respectively. Each <jats:italic>B. amyloliquefaciens sip(ba)</jats:italic> gene was expressed in an <jats:italic>Escherichia coli</jats:italic> LepB<jats:italic>ts</jats:italic> mutant and tested for genetic complementation of the temperature sensitive (TS) phenotype as well as pre‐OmpA processing. Although SipS(<jats:italic>ba</jats:italic>) as well as SipT(<jats:italic>ba</jats:italic>) efficiently restored processing of pre‐OmpA in <jats:italic>E. coli</jats:italic>, only SipS(<jats:italic>ba</jats:italic>) supported growth at TS conditions, indicating functional diversity. Changed properties of the <jats:italic>sip(ba)</jats:italic> gene disruption mutants, including cell autolysis, motility, sporulation, and nuclease activities, seemed to correlate with specificities and/or localization of <jats:italic>B. amyloliquefaciens</jats:italic> SipS, SipT and SipV isoforms.</jats:p>