Host-Associated Metabolites of the Marine Roseobacter-Group: Chemical Diversity, Biosynthesis, Ecological Functions and Bioactivities

Marine microorganisms, particularly members of the marine Roseobacter-group, participate in chemically mediated associations with phytoplankton, macroalgae, and marine invertebrates. This review examines structurally characterized, host-associated metabolites produced by Roseobacter-group bacteria within this ecological framework. These metabolites include sulfur-containing compounds, nitrogen-containing and hybrid scaffolds, pigments, lipids, and signaling molecules, exemplified by the antibacterial tropodithietic acid and the algaecidal roseobacticides. We discuss biosynthetic connections between phenylacetate and sulfur metabolism that give rise to tropodithietic acid and roseobacticides, as well as tryptophan–sinapic-acid-derived hybrid pathways. By integrating genomic potential, host-derived elicitors, metabolomics, structure elucidation, and experimentally demonstrated activities, this review distinguishes chemically characterized products from bioinformatically predicted pathways and proposed applications.