To further explore the potential role of Psychrilyobacter, Vibrio, and Mycoplasma in algal digestion, we compared their carbohydrate-active enzymes (CAZymes) and sulfatase contents to that of Zobellia galactanivorans DsijT, a model bacterium for the bioconversion of algal polysaccharides . This was done based on the public CAZy and SulfAtlas databases (Table 1, Additional file 4: Table S3 and Additional file 5: Table S4). This approach is of course limited by the availability of genomes of some genera in public databases. Still, similar results were found in several available genomes of a given genus and are likely to reflect at least some functions present in abalone digestive microbiota. As there was no Psychrilyobacter genome available in the CAZy and SulfAtlas databases, we manually annotated the CAZyme- and sulfatase-coding sequences in the only genome of the genus available to date in NCBI Genome , i.e., that of Psychrilyobacter atlanticus DSM 19335, a strictly anaerobic bacterium isolated from marine sediment . Compared to the genome of Z. galactanivorans DsijT, the genome of P. atlanticus DSM 19335, contains far fewer GHs and sulfatases as well as no polysaccharide lyases (Table 1, Additional file 5: Table S4). These genes are likely to enable the degradation of extracellular oligosaccharides, but not the degradation of complex algal polysaccharides (Additional file 5: Table S4). To evaluate the ability of Vibrio to degrade algal polysaccharides in the digestive gland, we examined the CAZyme and sulfatase content in the 127 Vibrio genomes available in the CAZy and SulfAtlas databases to date (Additional file 4: Table S3 and Additional file 5: Table S4). The 127 genomes present lower numbers of CAZyme and sulfatase families than the Z. galactanivorans genome (Table 1, Additional file 4: Table S3 and Additional file 5: Table S4). However, all examined Vibrio genomes contain at least one enzyme involved in chitin and/or cellulose metabolism (GH9, GH18, GH19, GH20, GH94 families) and at least one enzyme degrading extracellular oligosaccharides. Some Vibrio genomes such as V. crassostreae 9CS106, V. breoganii FF50, V. owensii XSBZ03, V. halioticoli NBRC 102217, three strains of V. alginolyticus (ATCC 33787, K08M4, and ATCC 17749), and V. harveyi also are able to degrade the red algal polysaccharide agarose (aga genes from families GH16, GH50), laminarin (lam genes family GH3), and/or alginate (alyA genes from families PL6, PL7, PL15, PL17) from brown algae (Additional file 4: Table S3, ). For Mycoplasma, we examined 111 genomes, which show poor capacities to degrade complex carbohydrates and no ability to degrade algal polysaccharides (Additional file 5: Table S4, ).Table 1Total number of putative glycoside hydrolase (GH), polysaccharide lyase (PL), and sulfatase genes in selected genomesGHaPLaSulfatasesReferencesPsychrilyobacter atlanticus DSM 1933513b23c0002127 Vibrio genomes9–2722–700–50–210–50–9[33, 34]111 Mycoplasma genomes0–60–120–10–100Z. galactanivorans DsijT441418151771This table also contains total number of GH, PL, and sulfatase families in selected genomes from the three genera of the core digestive microbiota of the abalone and of Zobellia galactanivorans DsijT, a model bacterium for algal polysaccharide degradation. For more details on the CAZyme and sulfatase content, see Additional file 4: Table S3 and Additional file 5: Table S4aCAZyme classbTotal number of CAZyme or sulfatase families in the given classcTotal number of CAZyme or sulfatase genes in the given classZ. galactanivorans Zobellia galactanivorans; GH glycoside hydrolase, PL polysaccharide lyase. Data retrieved from the CAZy and SulfAtlas databases (www.cazy.org, , http://abims.sb-roscoff.fr/sulfatlas/, )