Made and Modified The polytheonamides are 48-residue toxins derived from marine sponges that include 18 D -amino acids, as well as many other unusual amino acid modifications. Given the complexity, one might guess that these peptides are the product of nonribosomal, peptide synthetase (NRPS). However, Freeman et al. (p. 387 , published online 13 September now show that polytheonamides are produced by a bacterial symbiont using a ribosomal pathway. Six candidate enzymes for the 48 posttranslational modifications were identified and three were functionally validated. Such ribosomal systems could be useful in bioengineering.

Metagenome Mining Reveals Polytheonamides as Posttranslationally Modified Ribosomal Peptides