Study Of The Functional Genomes Of B.Longum Subsp.Infantis And Its Effects On DSS-induced Colitis

B.longum subsp.infantis is a subspecies of Bifidobacterium longum,which can be used in food.Studies have found that individual strains had some physiological functions such as immune regulation.At present,most of B.longum that had been researched and commercialized were B.longum subsp.longum,and the genomic characterization and prebiotic function of B.longum subsp.infantis were rarely studied.The development of gene sequencing technology had made it easier to distinguish B.longum subsp.infantis from other subspecies.Therefore,this study aimed to isolated B.longum subsp.infantis and analyze its genomic characteristics and functional gene differences through genome comparison.In addition,strains with different functional genes were chosen to explore their effects on dextran sulphate sodium(DSS)-induced colitis.And the association of functional genome differences in B.longum subsp.infantis with its effects on DSS-induced colitis were shown.The main results were as follows:(1)B.longum subsp.infantis was distinguished from other subspecies of B.longum by subspecies-specific gene amplification first.And then average nucleotide identity and phylogenetic analyses of B.longum were performed based on whole genome sequence.39 B.longum subsp.infantis were isolated finally.All other strains were derived from infant fecal samples,except for one strain isolated from breast milk.The genomic characteristics of B.longum subsp.infantis and differences in functional genes between different strains were obtained through functional genome comparison.B.longum subsp.infantis had obvious differences in exopolysaccharide gene clusters,carbohydrate utilization-related genes,clustered regularly interspaced short palindromic repeats(CRISPR)-CRISPR associated(Cas)systems,and bacteriocin operons.The predicted exopolysaccharide gene clusters were highly variable.And the genes related to plant-source carbohydrate metabolism such as arabinose were diverse.The presence or absence of CRISPR-Cas systems enhanced the genomic diversity of B.longum subsp.infantis.Additionally,the differences in bacteriocin operons between strains might reveal the different antibacterial capabilities of B.longum subsp.infantis.(2)According to the results of genome comparison,eleven B.longum subsp.infantis with significant differences in functional genes were selected to compare their effects on DSS-induced colitis.The results showed that these strains had different effects on DSS-induced colitis.B.longum subsp.infantis FJSYZ1M3 could significantly improve the symptoms of colitis;B.longum subsp.infantis FBJCP1M11,JSWX25M6,FBJCY2M11,and FZJJH13M4 had no significant effect on relieving colitis;and B.longum subsp.infantis FJND16M4,FHBSJZ50M1,FGZ17I1M1,ATCC15697,FGZ19I1M3,and JSWX6M2 had no alleviation on colitis,while B.longum subsp.infantis FJND2M2 exacerbated symptoms.The reasons for the different effects of B.longum subsp.infantis on DSS-induced colitis were further analyzed.The results showed that the ability of B.longum subsp.infantis to reduce the damage to the intestinal mechanical barrier,regulate the level of inflammatory cytokines,regulate the concentration of short-chain fatty acids,and relieve gut microbiota disturbance were different.The reasons for the different effects of B.longum subsp.infantis on DSS-induced colitis were explored at the gene level based on the association analyses between functional gene differences and their improvement of colitis.And the results showed that the improvement of B.longum subsp.infantis on colitis might be positively correlated with the existence of and number of carbohydrate utilization-related glycosylhydrolase 43 gene family and glycosylhydrolase 53 family.