Gut microbial diversity and function analysis of the final-instar larvae of Protohermes xanthodes (Megaloptera: Corydalidae)

Protohermes xanthodes (Megaloptera, Corydalidae, Protohermes), widespread species in China, is an important insects treated as food and medicine for aquaculture. In this study, the gut microbiota was investigated by 16S rRNA microbial profiling. A total of 600 Amplicon Sequence Variants (ASV) were identified, Proteobacteria and Firmicutes were the main dominant phyla, and 27 genera ran through the entire digestive tract, mainly Hafnia-Obesumbacterium (Proteobacteria), Lactobacillus and Lactococcus (Firmicutes). The PICRUSt2 functional prediction of gut microbiota showed that the foregut abundant pathways related to metabolism, environmental information processing, and genetic information processing. while the midgut had the most abundant metabolic and environmental information processing pathways, including the prominent phosphotransferase system (PTS), propionate metabolism, and β-lactam resistance. The hindgut had the weakest metabolic function, but its genetic information processing was more abundant than the foregut and midgut. Additionally, 26 strains of bacteria were isolated from the midgut microorganisms, with Firmicutes being the dominant bacteria, and some of the purified bacteria had potential probiotic and anti-pathogen functions. These findings suggest that there are differences in the microorganisms of the different gut floras of the larvae, and each flora has specific metabolic functions. This research could be used to further understand the function of gut microorganisms, explore the co-evolution of P. xanthodes and gut microorganisms, and promote healthy breeding based on gut microorganisms.