Metagenomic analysis of bacterial and viral diversity in the intestines of abalone (Haliotis discus hannai) and spoon worm (Urechis unicinctus)

Abstract

Abalone is one of typical invertebrate farmed in South Korea and several microorganisms producing novel cellulases and valuable compounds were found in abalone. In case of spoon worms, they inhabit almost all around the world, but they still have difficulty to be cultivated artificially. Moreover, almost studies researching abalones and spoon worms have been focusing on detecting and screening of novel microorganisms and compounds, whereas, few studies have researched microbial diversity in abalones and spoon worms so far. Therefore, in this study, bacterial and viral diversity in abalones and spoon worms were revealed using the recently revised metagenomic tools. Results showed that Mycoplasma species took over 70 % in the whole bacterial population in abalone intestine, whereas Vibrio species occupied about 10 %. In spoon worm samples, Lactic acid bacteria such as Lactococcus and Leuconostoc species were dominant occupying 63.6 % in the whole bacterial population. Viral diversity analysis revealed that 5.35 % sequences were matched with known viral sequences in abalone samples. Among known viral sequences, 53 % of known sequences were ds DNA viruses and 45 % were ss DNA viruses and 2 % were unclassified or RNA viruses. 0.1 % of the sequences were known viral sequences in spoon worm samples and 62 % of known viral sequences were ds DNA virus and 24 % were mostly related to ss DNA viruses and 14 % were unclassified phages. Viral compositions of both abalone and spoon worm samples were mainly occupied by ds DNA viruses such as Myoviridae, Sipoviridae and Podoviridae belonging to Caudovirales and ss DNA viruses such as Chlamydia phages related to Microviridae. Retroviruses and ss RNA viruses were also detected and they occupied less than 0.5 % only in abalone. Overall, the results from this study, are expected to be applied to the probiotic applications for abalone and spoon worm aquaculture as fundamental informations.