Many of the most potent antibiotics originate from bacteria. A large proportion belong to a class of compounds known as nonribosomal peptides (NRP). They are produced by large bacterial enzyme machineries—the nonribosomal peptide synthetases, or NRPS for short. These function like molecular assembly lines: Similar to the stations in a car factory, where new parts are added to the car at each step, several specialized modules string together amino acid by amino acid to build a peptide.