PROJECT SUMMARY Microbial phosphonic acids are a class of understudied natural products with significant utility in medicine. The antimicrobial, antiviral, and antimalarial activity of many useful phosphonic acids derives from potent and specific inhibition of metabolic enzymes through chemical mimicry of their natural substrates. These properties, along with the trove of novel biosynthetic gene clusters encoded within microbial genomic datasets, highlight their potential of phosphonic acid natural products new antimicrobials. In this project we focus our efforts on realizing their genomic potential of these compounds by establishing fundamental genetic and biochemical principles that define their biosynthetic and bioactivity landscape. Filling these gaps in knowledge will provide a systems-level understanding of natural product biosynthesis necessary to improve discovery and engineering of new phosphonic acids. Specifically, we investigate three recently discovered phosphonic acid peptides to uncover unusual hydroxylation, reduction, amination, and amino acid ligation enzymes, and the molecular basis of their antimicrobial activity. We expand and refine the framework for phosphonic acid natural product genomics through the isolation of new compounds from cryptic gene clusters, discovery of new pathways and enzymes for C-P bond formation, and the development of a classification scheme to improve prediction of phosphonic acid gene clusters and their chemical products.