Isolation and Complete Genome Sequence of Algibacter alginolytica sp. nov., a Novel Seaweed-Degrading Bacteroidetes Bacterium with Diverse Putative Polysaccharide Utilization Loci

Abstract

eThe members of the phylum Bacteroidetes are recognized as some of the most important specialists for the degradation of polysaccharides. However, in contrast to research on Bacteroidetes in the human gut, research on polysaccharide degradation by marine Bacteroidetes is still rare. The genus Algibacter belongs to the Flavobacteriaceae family of the Bacteroidetes, and most species in this genus are isolated from or near the habitat of algae, indicating a preference for the complex polysaccharides of algae. In this work, a novel brown-seaweed-degrading strain designated HZ22 was isolated from the surface of a brown seaweed (Laminaria japonica). On the basis of its physiological, chemotaxonomic, and genotypic characteristics, it is proposed that strain HZ22 represents a novel species in the genus Algibacter with the proposed name Algibacter alginolytica sp. nov. The genome of strain HZ22, the type strain of this species, harbors 3,371 coding sequences (CDSs) and 255 carbohydrate-active enzymes (CAZymes), including 104 glycoside hydrolases (GHs) and 18 polysaccharide lyases (PLs); this appears to be the highest proportion of CAZymes (ϳ7.5%) among the reported strains in the class Flavobacteria. Seventeen polysaccharide utilization loci (PUL) are predicted to be specific for marine polysaccharides, especially algal polysaccharides from red, green, and brown seaweeds. In particular, PUL N is predicted to be specific for alginate. Taking these findings together with the results of assays of crude alginate lyases, we prove that strain HZ22 T can completely degrade alginate. This work reveals that strain HZ22 T has good potential for the degradation of algal polysaccharides and that the structure and related mechanism of PUL in strain HZ22T are worth further research. Members of the phylum Bacteroidetes, formerly also known as the Cytophaga-Flavobacteria-Bacteroides cluster, constitute one of the major groups of marine heterotrophic bacterioplankton (1, 2). They have been found in various marine habitats, including coastal sediments (3), coastal waters (4, 5), hydrothermal vents (6, 7), and open ocean waters (8-10). In previous studies, marine Bacteroidetes have been reported as important contributors to the utilization of biopolymers such as polysaccharides and proteins (2,(11)(12)(13)(14). As a result, marine Bacteroidetes are assumed to play an important role in the degradation of algae. Marine phytoplankton have been estimated to be responsible for about 50% of global net primary production (15). Polysaccharides constitute a substantial fraction of the primary production from marine phytoplankton. Algae can be an important source of polysaccharides. Brown seaweeds, a traditional and plentiful mariculture product in East Asia, make up a large proportion of the total biomass of algae and synthesize a wide variety of compounds, such as alginate, fucoidan, laminarin, and mannitol (16). Among these compounds, alginate has been assumed to be a potential source for bioethanol production (17-19).The genus Algibacter belongs...

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