Changes Of Gut Microbial Of Atlantic Salmon Infected With Aeromonas Salmonidis And Its Intestinal Mechanism

Salmon salar,also known as salmon,has high economic and nutritional value,and it is an important commercial cultured fish in China.However,there are frequent diseases in the process of aquaculture,which seriously affects the healthy development of the Atlantic salmon industry in China,among which Aeromonas salmonicida(A.salmonicida)is the most common one.This bacterium often causes enteritis,furuncle and bacterial septicemia in fish,which can spread rapidly in a short time and cause large-scale death of Atlantic salmon,causing great economic losses to farmers.Fish intestines are inhabited by a large number of microorganisms,which are collectively called gut microbiota.These microflora improve host health by regulating metabolic processes and immune responses.It is of great significance to understand the gut microbiota structure and its dynamic changes of Atlantic salmon infected with A.salmonicida to promote the sustainable and healthy development of Atlantic salmon industry in China.In this study,16 sr RNA amplicon sequencing and liquid chromatography-mass spectrometry(LC-MS/MS)were used to analyze the effects of A.salmonicida infection on the structure and function of the gut microbiota of Atlantic salmon,so as to provide a theoretical basis for further exploring the interaction mechanism between intestinal flora and A.salmonicida.The main results are as follows:(1)Effects of A.salmonicida infection on gut microbiota of Atlantic salmonThe dominant bacteria in the intestine of Atlantic salmon are Proteobacteria,Firmicutes and Actinobacteriota,and the dominant genus is Pseudomonas.The changes of bacterial abundance in each experimental group were analyzed.Compared with the control group,only the abundance of Dongia in the low-concentration infection group(LI)decreased significantly,while 8 genera in the high-concentration infection group(HI)changed significantly and all showed an increasing trend,include Clostridium＿sensu＿stricto＿1,Romboutsia,Bacteroides,Blautia,Agathobacter,Parasutterella,Fusicatenibacter,Butyricicoccus.(2)Effects of A.salmonicida infection on intestinal metabolism of Atlantic salmonUsing LC-MS/MS technology,the effects of A.salmonicida infection on the intestinal metabolic spectrum of Atlantic salmon were preliminarily explored,in order to understand the differential metabolites and metabolic pathways related to pathogen infection.The results showed that there were 36 kinds of intestinal differential metabolites between LI group and Control group,including D-isocitrate,caproyl carnitine and 1-methylguanosine,and the metabolic pathway involved was the biosynthesis of unsaturated fatty acids.There are 358 kinds of intestinal differential metabolites between HI group and Control group,including 5-hydroxytryptophan,taurocholic acid and taurocholic chenodeoxycholic acid.The metabolic pathways involved are histidine metabolism,bile secretion,antibiotic biosynthesis and vitamin digestion and absorption.Pearson statistical method was used to analyze the correlation between these differential metabolites and the intestinal bacteria of Atlantic salmon.The results showed that in LI group,Dongia was positively correlated with gamicin and negatively correlated with1-methylguanosine.In HI group,Agathobacter was positively correlated with glycoursodeoxycholic acid,taurocholate and chenodeoxycholic acid,and negatively correlated with ascorbic acid.Fusicatenibacter is positively correlated with glycoursodeoxycholic acid and kanamycin,and negatively correlated with histamine in histidine metabolic pathway.To sum up,A.salmonicida may change the intestinal environment and regulate the intestinal metabolism by regulating the intestinal flora structure of fish.This study provides a theoretical basis for the prevention and control of A.salmonicida infection.