Three marine species of the genus Fulvivirga, rich sources of carbohydrate-active enzymes degrading alginate, chitin, laminarin, starch, and xylan

Bacteroidota is a group of marine polysaccharide degraders, which play a crucial role in the carbon cycle in the marine ecosystems. In this study, three novel gliding strains, designated as SS9-22(T), W9P-11(T), and SW1-E11(T), isolated from algae and decaying wood were proposed to represent three novel species of the genus Fulvivirga. We identified a large number of genes encoding for carbohydrate-active enzymes, which potentially participate in polysaccharide degradation, based on whole genome sequencing. The 16S rRNA sequence similarities among them were 94.4–97.2%, and against existing species in the genus Fulvivirga 93.1–99.8%. The complete genomes of strains SS9-22(T), W9P-11(T), and SW1-E11(T) comprised one circular chromosome with size of 6.98, 6.52, and 6.39 Mb, respectively; the GC contents were 41.9%, 39.0%, and 38.1%, respectively. The average nucleotide identity and the digital DNA-DNA hybridization values with members in the genus Fulvivirga including the isolates were in a range of 68.9–85.4% and 17.1–29.7%, respectively, which are low for the proposal of novel species. Genomic mining in three genomes identified hundreds of carbohydrate-active enzymes (CAZymes) covering up to 93 CAZyme families and 58–70 CAZyme gene clusters, exceeding the numbers of genes present in the other species of the genus Fulvivirga. Polysaccharides of alginate, chitin, laminarin, starch, and xylan were degraded in vitro, highlighting that the three strains are rich sources of CAZymes of polysaccharide degraders for biotechnological applications. The phenotypic, biochemical, chemotaxonomic, and genomic characteristics supported the proposal of three novel species in the genus Fulvivirga, for which the names Fulvivirga ulvae sp. nov. (SS9-22(T) = KCTC 82072(T) = GDMCC 1.2804(T)), Fulvivirga ligni sp. nov. (W9P-11(T) = KCTC 72992(T) = GDMCC 1.2803(T)), and Fulvivirga maritima sp. nov. (SW1-E11(T) = KCTC 72832(T) = GDMCC 1.2802(T)) are proposed.