Genome Analysis of Halomonas sp. 0522KB3.1, a Marine Bacterium Isolated from the Brown Alga Sargassum mcclurei, Reveals Potential for Fucoidan Modification

Abstract Halomonas sp. 0522KB3.1, a halophilic bacterium isolated from the brown alga Sargassum mcclurei, was investigated for its potential to modify sulfated marine polysaccharides. Functional screening revealed strong fucoidan-modifying activity on fucoidan-containing agar plates. Whole-genome sequencing and annotation identified 138 CAZymes, including 44 glycoside hydrolases (GHs), with GH29, GH95, and GH151 families linked to fucoidan processing. Among 15 predicted polysaccharide utilization clusters (PUL-like clusters), several harbored GH29, GH95, GH151 and sulfatase genes. Three hypothetical proteins (no.500, no.501, and no.376) were identified as candidate putative α-L-fucosidases possibly involved in fucoidan depolymerization based on sequence similarity to characterized GH29 and GH95 fucosidases and conserved catalytic motifs. Phylogenetic analysis clustered these proteins with known fucosidases, suggesting possible exo-type cleavage of fucosyl linkages. Despite the absence of canonical fucoidan-specific GH107/GH168 enzymes, the modular CAZyme-PUL—ike architecture suggests an alternative enzymatic strategy for modular processing of fucoidan. This study provides genome resolved, locus-level evidence for the fucoidan-modifying capacity of Halomonas sp. 0522KB3.1, expanding the genomic understanding of fucoidanolytic bacteria and highlighting this strain as a promising source of novel marine carbohydrate-active enzymes.