Inulin Modulates Composition Of Intestinal Microbiota In Mice

The human intestine is inhabited by a highly diverse microbial ecosystem dominated by hundreds of different species of anaerobic bacteria.The complex bacterial community plays a critical part in biological processes.Intestinal microbial community dysbiosis is the leading cause of numerous chronic diseases.It has been clearly demonstrated that environmental factors,particularly diet,have a considerable effect on the composition of intestinal microbiota besides the individual genotype.Obesity,accompanied by inflammation,has become a worldwide devastating epidemic in recent decades.Recent studies on intestinal microbiota have revealed the causative role of the gut microbial dysbiosis in obesity.However,the exact mechanisms are still under studies.Inulins are a polysaccharide linked by ?-(2-1)bonds through D-fructoses with a terminal glucose residue.And inulins can pass through the upper gut and reach the large intestine unabsorbed,modulates the intestinal microbial community,leading a beneficial effect on host.Inulins have been reported to stimulating growth or activity of beneficial bacteria and suppressing the levels of harmful bacteria selectively.However,influences of dietary inulin on intestinal microbiota were very complex.The effects of inulin on modulating intestinal microbiota were mainly concerned on given groups of bacteria during inulin consumption in previous studies.And little research to date has been focus on global gut microbiota communities during interventions of inulin.The high-throughput sequencing technologies have profoundly changed our understanding on diversity of intestinal microbiota.The study aimed to analyse the global influences of dietary inulin with different degrees of polymerization(DP)on intestinal microbial communities by 16 s r RNA sequencing technology.A direct consequence of inulin interventions is stimulation of Bifidobacteriaceae and Lactobacillaceae within intestinal microbiota,which is called bifidogenic effect.However influences of dietary inulin on modulating intestinal microbiota were far more complex than bifidogenic effects.The relative abundance of butyrate-producing bacteria,within Bacteroidales S24-7 group and Ruminococcaceae families were increased after FOS and inulin interventions.Akkermansia muciniphila,belonging to mucin-degrading species,became a dominant species in Verrucomicrobia phylum after inulin treatment.The modulation effects of inulin were positively correlated with DP and dosage.Lower DP interventions exhibited better effects than higher DP treatment on stimulation of probiotics.The increasing extent of some gut microbiota was always stronger in high dose groups than in other groups.The increasing abundance in Bacteroides vulgatus,which cannot use inulin,indicated a cross-feeding phenomenon.And we hypothesized that Akkermansia muciniphila played an important role on maintaining balance between mucin and short chain fatty acids(SCFAs).In order to investigate the influences of dietary FOS on intestinal microbial communities in high fat diet(HFD)induced obesity mice,the V4 and V5 hypervariable 16 S rRNA region were selected for sequencing based on Illumina Hiseq PE250 paltform.The ratio of Firmicutes to Bacteroides increased significantly in HFD group.The relative abundance of butyrate-producing bacteria,within Bacteroidales S24-7 group and Ruminococcaceae families were decreased in HFD group.And gram-negative opportunistic,endotoxin producing pathogens,such as Escherichia-Shigella,Parabacteroides and Bacteroides,increased significantly in HFD group.FOS intervention decreased the ratio of Firmicutes to Bacteroides.An increase in probiotics and a decrease in opportunistic pathogens were also found with FOS supplement.Real-time quantitative PCR was used to identify the expression level of lipometabolism and inflammation related genes in liver and adipose.The excessive fat accumulation in the HFD-fed mice was associated with a leptin-resistant phenotype.And the expression level of mRNA increased significantly in HFD group.However,FOS intervention decreased the level of mRNA compared with HFD group.The level of lipopolysaccharides(LPS)may be the leading cause of obesity and inflammation.We hypothesized that the mechanism of FOS on reducing obesity and inflammation: on the one hand,FOS could modulate the structure and composition of intestinal microbiota,as well as enchance the function of intestinal barrier.Furthermore,FOS could stimulate the growth or activity of beneficial bacteria and suppress the levels of gram-negative opportunistic,endotoxin producing pathogens selectively.On the other hand,the SCFAs,which were generated by intestinal microbiota fermentation,could have reduced pH in micro-environment of intestinal tract,as a consequence of suppressing the levels of opportunistic pathogens.Besides,SCFAs could modulate energy metabolism,reducing the process of obesity.This study has a guiding effect for inulin on modulating intestinal microbiota in mice,as well as understanding the occurrence and prevention of obesity.