Gastrointestinal tract microbial community of Babylonia areolata and its diversity are closely correlated with the outbreak of disease

The intestinal microbiome is important for the health of aquatic animals. However, in Babylonia, the combination of gastrointestinal tract (GI) bacterial symbionts has barely been explored. In this study, from a farm with naturally occurring diseases, we collected Babylonia areolata in three different states, that is “diseased” (group D), “health” (group H) and “subhealth” (group SH) and aimed to reveal the relationship between disease occurrence and GI microbiota of B. areolata. Diversity analysis illustrated that GI microbial diversity of group D was obviously lower than that of group H on phylum level and genus level, and GI microbial diversity of group SH was between group D and H. KEGG analysis showed that the physiological activities of pathogenic microorganisms in group D increased significantly, compared with group H. Metagenomics analysis demonstrated the expressions of virulence genes in group D enhanced obviously, compared with group H. In addition, the diversity of culturable microorganisms from the GI contents of group D was dramatically lower than that of group H. A total of 22 species were obtained from the GI contents of group H. However, only four species were obtained from group D, and two important pathogens, Vibrio harveyi and Vibrio tubiashii, were dominant microbiota. These results indicate that the decline of GI microbial diversity in B. areolata is highly associated with the occurrence of disease. We speculated environmental factors led to the decline of GI microbial diversity, which could promote propagation of pathogenic microbes (such as V. harveyi and V. tubiashii). Our findings provide new insights into the disease outbreak of B. areolata and provide propose that the preservation of GI microbial diversity at the early phases can effectively prevent the occurrence of disease.