Bacterial tropone natural products and derivatives: Overview on the biosynthesis, bioactivities, ecological role and biotechnological potential.

Tropone natural products are non-benzene aromatic compounds of significant ecological and pharmaceutical interest. Here we highlight current knowledge on bacterial tropones and derivatives such as tropolones, tropodithietic acid, and roseobacticides. Their unusual biosynthesis depends on a universal CoA-bound precursor featuring a seven-membered carbon ring as backbone, which is generated by a side reaction of the phenylacetic acid catabolic pathway. Then, enzymes encoded by separate gene clusters further modify this key intermediate, which may comprise oxidation, CoA-release, or incorporation of sulfur among other reactions. Tropones adopt important roles in the terrestrial and marine environment where they act as antibiotics, algaecides, or quorum sensing signals, while their bacterial producers are often involved in symbiotic interactions with plants and marine invertebrates (e.g., algae, corals, sponges, or mollusks). Because of their potent bioactivities and of slowly developing bacterial resistance, tropones and derivatives hold great promise for biomedical or biotechnological applications, for instance as antibiotics in (shell)fish aquaculture.