Pseudooceanicola algae sp. nov., isolated from the marine macroalga Fucus spiralis, shows genomic and physiological adaptations for an algae-associated lifestyle.

The genus Pseudooceanicola from the alphaproteobacterial Roseobacter group currently includes ten validated species. We herein describe strain Lw-13e, the first Pseudooceanicola species from marine macroalgae, isolated from the brown alga Fucus spiralis abundant at European and North American coasts. Physiological and pangenome analyses of Lw-13e showed corresponding adaptive features. Adaptations to the tidal environment include a broad salinity tolerance, degradation of macroalgae-derived substrates (mannitol, mannose, proline), and resistance to several antibiotics and heavy metals. Notably, Lw-13e can degrade oligomeric alginate via PL15 alginate lyase encoded in a polysaccharide utilization locus (PUL), rarely described for roseobacters to date. Plasmid localization of the PUL strengthens the importance of mobile genetic elements for evolutionary adaptations within the Roseobacter group. PL15 homologs were primarily detected in marine plant-associated metagenomes from coastal environments but not in the open ocean, corroborating its adaptive role in algae-rich habitats. Exceptional is the tolerance of Lw-13e against the broad-spectrum antibiotic tropodithietic acid, produced by Phaeobacter spp. co-occurring in coastal habitats. Furthermore, Lw-13e exhibits features resembling terrestrial plant-bacteria associations, i.e. biosynthesis of siderophores, terpenes and volatiles, which may contribute to mutual bacteria-algae interactions. Closest described relative of Lw-13e is Pseudopuniceibacterium sediminis CY03 with 98.4% 16S rRNA gene sequence similarity. However, protein sequence-based core genome phylogeny and average nucleotide identity indicate affiliation of Lw-13e with the genus Pseudooceanicola. Based on phylogenetic, physiological and (chemo)taxonomic distinctions, we propose strain Lw-13e (=DSM 29013=LMG 30557) as a novel species with the name Pseudooceanicola algae.