The Role Of Intestinal Microbiota In High-fat Diet Induced Fat Accumulation Of Nile Tilapia

Aquaculture is one of the fastest growing industries in China.Protein,lipid and carbohydrate in diet are important sources of energy for fish.Considering the limit amount of fish meal,how to increase the utilization efficiency of other dietary components is an important question in aquaculture.Lipid can provide essential fatty acids and energy to fish,but excessive lipid intake can easily cause lipid accumulation in fish.Gut microbiota play important roles in nutrients metabolism.Studies in human and mice have shown that gut microbiota is involved in lipid metabolism.How gut microbiota influence the lipid metabolism in fish remains unclear.In this study,Tilapia fed with 5% soybean oil and 11% soybean oil for 8 weeks and the result indicated that total lipid composition increased in high fat diet.The abundance of the major bacterial groups have been detected and the results showed that the abundance of ?-Proteobacteria and Actinomyces in the 11% soybean oil group was significantly higher than the 5% soybean oil group,suggesting that dietary lipid concentration increased total lipids in tilapia and altered the composition of the intestinal microbiota.In order to further explore the role of gut microbiota in fat accumulation in fish,we enriched and isolated one bacteria from the gut of tilapia in vitro.Sequencing indicated this bacteria belongs to Citrobacter freundii.Through antibiotic screening,the bacteria was labeled with rifampicin resistance.The diet with high soybean oil added with or without bacteria were fed to tilapia for 7 weeks.The results showed that the bacteria could reach the intestine of tilapia successfully.The additive of bacteria induced the abdominal fat accumulation significantly(P<0.05),increased the blood TG content(P<0.05),and upregulated the expression level of DGAT2,which is responsible for the intestinal triglyceride synthesis.We also found additive of the bacteria increases of TG content in blood at 1.5 hours after feeding compared with the control group.The length of intestinal villi was significantly decreased(P<0.05)and the expression of intestinal Claudin1,Claudin15,TJP1 and Occuldin decreased.The bacteria,whose nearest neighbor is Citrobacter freundii,may impair the intestinal connections,increase the transportation of dietary lipid into the blood,and ultimately cause fish fat accumulation.This study sheds light on the possible mechanisms of intestinal microbes in the accumulation of fat in fish,and provide a basis for regulating fish intestinal ecological balance.