Teicoplanin stress-selected mutations increasing sigma(B) activity in Staphylococcus aureus

A natural rsbU mutant of Staphyococcus anreus, unable to activate the alter native transcription factor sigma (B) via the RsbU pathway and therefore fo rming unpigmented colonies, produced first-step teicoplanin-resistant mutan ts upon selection far growth in the presence of teicoplanin, of which the m ajority were of an intense orange color. Ey using an asp23 promoter-lucifer ase fusion as an indicator, the pigmented mutants were shown to express inc reased sigma (B) activity. Increased sigma (B) activity was associated with point mutations in rsbW, releasing sigma (B) from sequestration by the ant i-sigma factor RsbW, or to promoter mutations increasing the sigma (B)/RsbW ratio. Genetic manipulations involving the sigB operon suggested that the mutations within the operon were associated with the increase in teicoplani n resistance, The upregulation of sigma (B) suggests that a sigma (B)-contr olled gene(s) is directly or indirectly involved in the development of teic oplanin resistance in S. aureus. Carotenoids do not contribute to teicoplan in resistance, since inactivation of the dehydrosqualene synthase gene crtM abolished pigment formation without affecting teicoplanin resistance, The relevant sigma (B)-controlled target genes involved in teicoplanin resistan ce remain to be identified.