Multi-tier regulation of the streptomycete morphogenetic peptide SapB

Streptomyces coelicolor is a morphologically complex bacterium requiring the secretion of surface-active proteins to progress through its life cycle. SapB represents an important class of these biosurfactants, as illustrated by its ability to restore aerial hyphae formation when applied exogenously to developmental mutants. However, such aerial hyphae fail to sporulate, exemplifying the need to co-ordinate the timing of SapB production with other developmental events. SapB has an unusual lantibiotic structure. Its structural gene, ramS, is only 38 nucleotides downstream of the gene encoding its putative modification enzyme, RamC. Transient, co-ordinated expression of the operon was thought to be controlled by the response regulator RamR. However, we show that ramS is transcribed throughout the cell cycle with a dual expression profile dissimilar to the tightly controlled ramC expression. Surprisingly, post-translational modification relies on prior membrane localization of the precursor peptide, RamS, as demonstrated by the absence of RamS modification in S. coelicolor hyphae treated with the Bacillus subtilis lipoprotein surfactin. Our results demonstrate that interspecies interaction can also be mediated by interference of post-translational events. Further, temporal and spatial regulation of irreversible post-translational modification of a surface-active morphogenetic peptide suggests a new model for the control of key developmental events.