Six new bacterial species isolated from the phycosphere of marine macroalgae: a joint analysis based on taxonomy and polysaccharide utilization loci
Abstract
Marine macroalgae-associated <i>Bacteroidota</i> play crucial roles in global carbon cycling through polysaccharide degradation, yet their taxonomic and functional diversity remains understudied. Here, we describe six novel species (strains 3-376<sup>T</sup>, 4-2040<sup>T</sup>, 2-473A<sup>T</sup>, 4-528<sup>T</sup>, 4-911<sup>T</sup> and 463<sup>T</sup>) within the families <i>Flavobacteriaceae</i>, <i>Crocinitomicaceae</i>, and <i>Cytophagaceae</i> isolated from macroalgal surfaces in the coastal area of Weihai, China. Metagenomic read recruitment and 16S rRNA abundance analyses demonstrated host-specific associations. Integrative taxonomic analyses, including phylogenomics (120 conserved proteins), 16S rRNA sequencing, and chemotaxonomy (e.g., MK-6 quinones, phosphatidylethanolamine lipids, and iso-C<sub>15:0</sub> fatty acids), confirmed their novel status, with average amino acid identity (AAI), percentage of conserved proteins (POCP) distinguishing them from related taxa. Genomes (3.3-7.1 Mb; G + C 31.7-45.3%) revealed diverse polysaccharide utilization loci (PULs) targeting algal glycans like laminarin, alginate, and sulfated polymers (ulvan, chondroitin sulfate). <i>Cytophagaceae</i> 463<sup>T</sup> harbored the richest CAZyme/PUL repertoire (131 CAZymes, 15 PULs), while <i>Crocinitomicaceae</i> 4-911<sup>T</sup> lacked PULs, highlighting family-level specialization. This study expands the known diversity of core phycosphere <i>Bacteroidota</i>, linking PUL evolution to habitat specialization. The novel species' distinct degradative capacities underscore their ecological roles in algal carbon processing and potential for biotechnological applications. Our integrated taxonomy-genomics approach advances understanding of microbial contributions to marine ecosystem dynamics.