A novel SAR324 bacterium associated with abalone, Haliotis diversicolor

摘要

Bacteria affiliated to the Deltaproteobacteria dominate intestinal microbial communities in the abalone, Haliotis diversicolor, and may colonize the host's digestive gland, raising the possibility that they contribute to digestion of macroalgae. However, the phylogenetic, and genomic and metabolic characteristics of these Deltaproteobacteria, and the nature of their relationship to abalone host remain elusive. Here, we examined the intestinal microbial composition of H. diversicolor using high-throughput sequencing and described the genomic characteristics of the Deltaproteobacteria phylotype using genome-centric metagenomics. High-throughput sequencing confirmed that one Deltaproteobacteria phylotype was predominant in intestinal microbiota of H. diversicolor. Phylogeny analysis based on full-length 16S rRNA gene allocated this bacterium to a distinct and unique cluster within SAR324. It possessed a genome of at least 1.59 Mb with 35.15 mol% GC content, much smaller than other sequenced free-living SAR324 bacteria. According to genome annotation and metabolic reconstruction, ATP binding cassette transporters for sugars and carbohydrate metabolism pathways indicated heterotrophic potential. Interestingly, it encoded polysaccharide lyases, which, if expressed, could help the host to digest its macroalgae diet. In contrast to the known SAR324, no sulphur oxidation or carbon fixation pathways were predicted. We propose that this is a unique and specific SAR324 bacterium in symbiosis with Haliotis.