GENES INVOLVED IN SELF-PROTECTION AGAINST THE LANTIBIOTIC SUBTILIN PRODUCED BY BACILLUS-SUBTILIS ATCC-6633

Subtilin is a ribosomally synthesized peptide antibiotic produced by Bacillus subtilis ATCC 6633. Recently, we reported regarding genes spaB, spaT, and spaC (C. Klein, C. Kaletta, N. Schnell, and K.-D. Entian, Appl. Environ. Microbiol. 58:132-142, 1992) which are involved in the biosynthesis of subtilin, and genes spaR and spaK (C. Klein, C. Kaletta, and K.-D. Entian, Appl. Environ. Microbiol. 59:296-303, 1993), which regulate subtilin biosynthesis via a histidine kinase/response regulator system. Further sequence analysis revealed the presence of three additional open reading frames, spaI; spaF, and spaG, downstream of the structural gene spaS. The spaI gene encodes a hydrophilic 19.3-kDa lipoprotein containing a consensus signal sequence, indicating that this protein might be membrane anchored. A similar gene, nisI, has been identified in the nisin producer. SpaF shows strong homology to members of the family of ABC transporters. spaG encodes a hydrophobic protein which might form the active transporter together with SpaF. Gene disruption mutants in all three genes were still able to produce subtilin; however, these mutants were more sensitive to subtilin than the wild-type strain. These results show that these genes are involved in the immunity mechanism of the producer strain. A similar involvement of an ABC transporter in the self-protection mechanism has been described for the McbE and McbF transporter, which confers immunity against microcin B17 in Escherichia coli. Mutants containing mutations in the genes spaR and spaK, which are responsible for regulation of subtilin biosynthesis, also became more sensitive to subtilin. This result shows that the immunity mechanism also seems to be regulated by the histidine kinase-response regulator system consisting of SpaR and SpaK.