Linking biosynthetic genes to natural products using inverse stable isotopic labeling (InverSIL)

The sequencing of microbial genomes has far outpaced their functional annotation. Stable isotopic labeling can be used to link biosynthetic genes with their natural products; however, the availability of the required isotopically substituted precursors can limit the accessibility of this approach. Here, we describe a method for using inverse stable isotopic labeling (InverSIL) to link biosynthetic genes with their natural products. With InverSIL, a microbe is grown on an isotopically substituted medium to create a fully substituted culture, and subsequently, the incorporation of precursors of natural isotopic abundance can be tracked by mass spectrometry. This eliminates issues with isotopically substituted precursor availability. We demonstrate the utility of this approach by linking a luxI-type acyl-homoserine lactone synthase gene in a bacterium that grows on methanol with its quorum sensing signal products. In the future, InverSIL can also be used to link biosynthetic gene clusters hypothesized to produce siderophores with their natural products.