Summary Bacteroidetes are thought to be specialized for the degradation of algae‐derived ocean polysaccharides. Here, we show that Bacteroidetes are the predominant phylum in deep‐sea sediments and possess more genes associated with polysaccharides degradation than other bacteria. We have isolated a novel Bacteroidetes species from the deep‐sea sediments by using a special polysaccharide containing medium, Maribellus comscasis...