1Dept. of Life Sci. & Med. Biosci., Waseda Univ., 2CREST, JST, 3Res. Org. for Nano & Life Innovation, Waseda Univ., 4Marine Genomics Unit, OIST, 5Institute for Chemical Research, Kyoto Univ.
【Introduction】Corals and coral-associated microorganisms such as zooxanthellae (a group of microalgae), bacteria and archaea compose a host-symbiont community called holobiont. The molecular mechanisms under coral-zooxanthellae symbiosis have begun to be revealed based on their genomic sequences decoded recently (Shinzato et al., 2011; Shoguchi et al., 2013). On the other hand, the roles of coral-associated bacteria in coral holobiont have scarcely been understood. Here, we analyzed genomic sequences of 36 bacterial strains newly isolated from a reef coral Acropora tenuis.
【Materials and methods】A. tenuis specimens were collected around Sesoko-island in Okinawa, Japan, in April, July and November 2014 and February 2015. Bacterial strains were isolated from tissue fractions of A. tenuis on marine broth agar media. Genomic DNA samples of the coral-associated bacteria were sequenced with MiSeq. Functional potential was evaluated MAPLE (Takami et al., 2014).
【Results and discussion】A total of 210 strains were isolated. 16S rRNA gene analysis showed that the isolates contained at least 32 independent strains over 20 genera and four phyla. We sequenced 36 genomes including those of the 32 representatives and other four isolates from different sampling dates or sites. The values of genome completeness were estimated to be 97.9 to 99.3%. Comparative analysis of functional potential in each genome suggested distinctive functional features in coral-associated bacteria. For example, in case of bacteria belonging to the families Mycobacteriaceae and Bacillaceae, no gene set for sulfate transportation was found in coral-associated bacteria, although non-coral associated bacteria examined in this study had it. It was reported that organic sulfates locate at calcification cores of coral skeletons (Cuif et al., 2003). Coral-associated Mycobacteriaceae and Bacillaceae might not utilize extracellular sulfate that is important for calcification on the skeletons.