Animal-associated marine Acidobacteria with a rich natural-product repertoire

Sponges are well known as rich sources of bioactive natural products. Various studies suggest that many of these compounds are produced by symbiotic bacteria. However, substance supplies and functional insights about the producers remain limited because cultivation remains unsuccessful. To identify alternative, sustainable sources of sponge-derived polyketides, we computationally analyzed 5,289 characterized and orphan trans-acyltransferase polyketide synthases, enzymes with widespread roles in polyketide biosynthesis by bacterial symbionts. The workflow predicted animal-derived marine Acidobacteria of the family Acanthopleuribacteraceae with large sets of biosynthetic gene clusters to be enriched in sponge-type chemistry. Targeted compound isolation from a chiton-associated strain yielded congeners of the phorboxazoles and calyculins, potent and scarce cytotoxins exclusively known from sponges, and depsipeptides named acidobactamides. These first natural products of Acidobacteria and new fire coral metagenomic data on a third family member suggest animal-associated Acanthopleuribacteraceae as a rich source of sponge-type and other metabolites.