:bacteria of the genusMassiliarepresent an underexplored source ofbioactive natural products. Here, we report the discovery of massinidine (1), aguanidine alkaloid with antiplasmodial activity, from these microbes. The unusualscaffold of massinidine is shown to originate fromL-phenylalanine, acetate, andL-arginine. Massinidine biosynthesis genes were identified in the native producer andvalidated through heterologous expression inMyxococcus xanthus. Bioinformaticanalyses indicate that the potential for massinidine biosynthesis is distributed invarious proteobacteria