Leucanicidin and Endophenasides Result from Methyl-Rhamnosylation by the Same Tailoring Enzymes in Kitasatospora sp. MBT66.

The increasing bacterial multidrug resistance necessitates novel drug-discovery efforts. One way to obtain novel chemistry is glycosylation, which is prevalent in nature, with high diversity in both the sugar moieties and the targeted aglycones. Kitasatospora sp. MBT66 produces endophenaside antibiotics, which is a family of (methyl-)rhamnosylated phenazines. Here we show that this strain also produces the plecomacrolide leucanicidin (1), which is derived from bafilomycin A1 by glycosylation with the same methyl-rhamnosyl moiety as present in the endophenasides. Immediately adjacent to the baf genes for bafilomycin biosynthesis lie leuA and leuB, which encode a sugar-O-methyltransferase and a glycosyltransferase, respectively. LeuA and LeuB are the only enzymes encoded by the genome of Kitasatospora sp. MBT66 that are candidates for the methyl-rhamnosylation of natural products, and mutation of leuB abolished glycosylation of both families of natural products. Thus, LeuA and -B mediate the post-PKS methyl-rhamnosylation of bafilomycin A1 to leucanicidin and of phenazines to endophenasides, showing surprising promiscuity by tolerating both macrolide and phenazine skeletons as the substrates. Detailed metabolic analysis by MS/MS based molecular networking facilitated the characterization of nine novel phenazine glycosides 6-8, 16, and 22-26, whereby compounds 23 and 24 represent an unprecedented tautomeric glyceride phenazine, further enriching the structural diversity of endophenasides.