| Chinese mitten crab(Eriocheir sinensis),also known as river crab,hairy crab,etc.,is a kind of crustacean with high economic value and the huge aquaculture industry.Gut/intestinal microbes,as the name suggests,are a class of tiny organisms that exist in the gut in organisms,and play an important role in the molting,growth and development of Eriocheir sinensis.In this paper,the variety of Eriocheir sinensis "Jianghai 21" was used to compare the changes of intestinal microbes of this crab with different genetic characteristics(the three kinds of SNP genotypes in MSTN gene),and developmental situations(molting stages and growth differences).The main goals were to find dynamic changes of composition and diversity of intestinal microbes of Chinese mitten crab with different genetic and developmental backgrounds,and to provide a guideline in aquaculture industry of this species.The main findings of the paper are as follows:1.Dynamic changes of intestinal microbes of Eriocheir sinensis during the molting processTo understand composition characteristics and dynamic changes of intestinal microbes in Chinese mitten crab(Eriocheir sinensis)during the molting process,the 16 S r RNA high-throughput sequencing technology was employed to investigate the composition,diversity and differences of intestinal microbes at different molting stages(pre-molting,inter-molting and post-molting stages)of this crab.The results showed that the dominant phyla of the intestinal microbes of Eriocheir sinensis were Proteobacteria,Firmicutes and Actinobacteriota,and Proteobacteria was absolutely dominant taxa.The Chao and Sobs index of Alpha diversity showed that there was no significant difference,but the Shonnon and Simpson diversity indexes were significant difference(P<0.01)between the post-molting stage and the inter-molting,pre-molting stages.PCo A analysis and ANOSIM test also confirmed that there were significant differences(P<0.01)between the post-molting stage and the inter-molting,pre-molting stages.At the phylum level,the abundance of Proteobacteria at the post-molting stage was significantly higher than that at the inter-molting and pre-molting stages(P<0.01).While the abundance of Firmicutes and Actinobacteria at the inter-molting and pre-molting stages were higher than that at the post-molting stage.At the genus level,the abundances of pseudomonas and alcaligenes were the highest at the post-molting stage(P<0.01),and exhibited the trends of decreasing at the post-molting stage and increasing at the pre-molting stage.The present results showed that the obvious relationship between composition of intestinal microbes and molting stage in Eriocheir sinensis,molting process should made a significant affect on composition and content of intestinal microbes.2.Intestinal microbial composition between normal and precocious Eriocheir sinensisIn order to explore whether the precocious puberty phenomenon of one-autumnyear-old precocious crabs and normal crabs in the same period is related to the intestinal flora.In this study,paraffin sections and H&E staining were used for histological observation of gonads and intestines,and then 16 S r RNA high-throughput sequencing technology was used to analyze the intestinal microbes of precocious crabs and normal crabs.There was no significantly histological difference in the intestinal tissue between the precocious crabs and the normal crabs.In both Alpha and Beta diversities,there was no significant difference in intestinal microbial composition and abundance between precocious crabs and normal crabs(P>0.05).At the phylum level,the dominant phyla of both crabs were Firmicutes,Proteobacteria and Bacteroidetes.The ratio of Firmicutes to Bacteroidetes was shown to be about twice as high as that of normal crabs in the composition of the intestinal microbes of precocious crabs.At the genus level,the dominant taxa of precocious crabs were Candidatus＿Bacilloplasma,Candidatus＿Hepatoplasma,Roseimarinus,Shewanella,and Bacteroides,but the dominant genera of normal crabs were Aeromona,Candidatus＿Bacilloplasma,Rosemary,unclassified＿c＿Alphaproteobacteria and Shewanella.The results of this study showed that there were no significant differences in the intestinal structure and microbial composition of the precious crabs and normal crabs.Therefore,it can be speculated that intestinal microbes would be a direct reason causing sexual precocity in Eriocheir sinensis.3.Comparative study on intestinal microbes of Eriocheir sinensis with different MSTN genotypesIn this chapter,the Chinese mitten crab with the three kinds of genotypes(TT/TC/CC in MSTN gene),named as M line(TT genotype)and F line(TC/CC genotypes)in present study,were used to investigate growth and intestinal microbes differences between them.The results showed that there was no significant difference in the weight gain rate and shell length between the two lines(P > 0.05).Using 16 S r RNA high-throughput sequencing technology,there was no significant difference in Alpha diversity index and Beta index of intestinal microbes between the two lines(P>0.05).The dominant phyla in both lines were Firmicutes,Bacteroidetes,Proteobacteria,Campilobacterota and Fusobacteriota,and the proportion of each phylum was different but not significant.Meanwhile,the top three dominant bacterial phyla were the same as the dominant bacterial phyla in the precocious and normal crabs in the Chapter 3(P>0.05).At the genus level,the top five dominant genera were Bacteroides,Candidatus＿Bacilloplasma,Malaciobacter,Parabacteroides,and Candidatus＿Hepatoplasma,which were similar to the dominant phyla,and the dominant genera were also similar between the two lines.(P>0.05).The results of this study showed that there were no significant difference in growth and intestinal microbes between the M and F lines of Eriocheir sinensis. |
