Molecular approaches enable the identification of genes that operate in natural product biosynthetic pathways. Microbes containing mutations in those genes can be fed alternative precursors, generating derivatives of complex natural products, which may not be obtainable by chemical methods.
Wohlleben, W., & Pelzer, S. (2002, November 1). New compounds by combining “Modern” genomics and “Old-Fashioned” mutasynthesis. Chemistry and Biology. https://doi.org/10.1016/S1074-5521(02)00267-3