Effects of temperature, diet and genotype-induced variations on the gut microbiota of abalone

Abalone is one of the most commercially important seafood, while its fisheries and aquaculture activities are carried out in 20 countries worldwide. Gut microbiota plays critical roles in the physiological functions of aquatic animals, and it is influenced by numerous factors. Previous studies about the gut microbiota of abalone usually focused on analyzing bacterial taxonomy or the impact of a single abiotic factor. However, the effect of abiotic factors, combined with biotic factors (i.e., genotype), on gut microbiota of abalone has not been systematically explored. In China, the hybrid Haliotis discus hannai. x H. fulgens. has potential for large-scale farming in southern China by its fast growth rate and tolerance to higher temperature. In this study, we analyzed the effects of diet, temperature and genotypes on gut microbiota of abalones using 16S rRNA gene sequencing data. The experiments indicate that the top three dominant genera keep consistent across various temperatures, diets and genotypes. The alpha-diversity of the microbial community was affected by temperature, genotype and diet. On the whole, the alpha-diversity of the gut microbiota of H. discus hannai was higher than that of the hybrid under the same temperature or diet. For beta-diversity, the microbial samples exhibited clear groups under abiotic gradients of temperature and diet. Some of the identified temperature-specific and diet-specific OTUs and KEGG Orthologs are related with degradation of carrageenan, laminaran and agar; metabolism of carbohydrate; biosynthesis of secondary metabolites and antibiotics, etc. According to permutational multivariate ANOVA, temperature and diet could explain almost 52% of bacterial structure variation. The gut microbiota of the two abalone genotypes have different responses to environmental gradients of temperature and diet. The gut microbiota of H. discus hannai is more sensitive to temperature, while the hybrid is more sensitive to diet, which might be the potential explanation of its tolerance to higher temperature in breeding. This study makes the first attempt to correlate the structural variation of gut microbiota in abalone by considering both abiotic and biotic factors.