Research On Glycan Utilization And Interspecies Cross Feeding Activities Of Bifidobacterium

Bifidobacteria are among the colonizers of the human gastrointestinal tract,and it has functions such as relieving constipation and enhancing immunity.Studies have shown that bifidobacteria can use different non-digestible carbon sources to growth,and they have a cross-feeding effect with other microorganisms in the intestine,thereby benefiting the health of the host.However,the current research on the utilization of carbon sources and cross-feeding activities of bifidobacteria is still limited to a few species and strains.In order to reveal the carbon sources utilization characteristics of bifidobacteria and the mechanism of interspecies cross feeding activities,this study focused on the 6 bifidobacterial species common in the Chinese people(Bifidobacterium longum,Bifidobacterium breve,Bifidobacterium adolescentis,Bifidobacterium bifidum,Bifidobacterium infantis,and Bifidobacterium pseudocatenulatum).First,determine utilization phenotype of bifidobacteria in 22 carbohydrates from different sources,and combine the genome to comprehensively analyze the distribution characteristics and distribution sites of each glycoside hydrolase,as well as the characteristics of gene clusters related to specific carbohydrate utilization.The carbohydrates utilization preference of bifidobacteria on the mixed carbohydrates was analyzed,and finally the possible interspecies cross feeding relationship of bifidobacteria on specific carbon sources was verified and evaluated.The main results are as follows:The carbohydrate utilization phenotype database of bifidobacteria was established.Through the determination of the utilization of 22 carbohydrates,this study found that the utilization phenotypes of the six bifidobacteria have differences between species and strains.At the species level,B.adolescentis,B.pseudocatenulatum and B.longum prefer to use plant carbon sources,among which B.pseudocatenulatum strains use plant carbon sources with the highest proportion.B.bifidum,B.infantis,and B.breve prefer to use host-derived carbon sources,and the use of mucin by B.bifidum has species specificity.Analyzed the distribution characteristics and location of glycoside hydrolase(GH)of bifidobacteria.We further reveal the analysis of the carbohydrate utilization mechanism of bifidobacteria from bifidobacterial genomes.In this study,through the analysis of the GH genes in the bifidobacteria genome,it was found that 6 bifidobacterial species co-encode GHs from 49 families.The number of glycoside hydrolase genes encoded by B.pseudocatenulatum is the largest,with an average of 58,and the glycoside hydrolase genes encoded by the B.bifidum genome are the least with an average of 31.Analyzed the related carbohydrates utilization gene clusters encoded by bifidobacteria,and established the correlation between phenotype and genotype.Moreover,this study reveal the molecular mechanism of carbon sources utilization by bifidobacteria from the perspective of gene clusters.By analyzing the homology of the genome of each strain,and correlating the results with phenotypic data,genes clusters related to 9 carbohydrate metabolism are discovered,and explore its distribution characteristics,structure,and differences between species and plants.For example,there are 3 types of 2'FL utilization gene clusters in Bifidobacterium,which are distributed in the genomes of B.breve,B.pseudocatenulatum,B.infantis,and B.bifidum.There are differences between the 2'FL utilization gene cluster structure of B.breve strains,and these structural differences are important distinguishing signs of whether B.breve can use 2'FL.Analyzed the preference of bifidobacteria to use mixed carbon sources.Select the combination of fructooligosaccharide,galactooligosaccharide,isomaltoligosaccharide,arabinogalactan,mannose-oligosaccharide and glucose,and analyze the utilization preference of 4 bifidobacterial species by measuring growth curves,generation time and biomass on the oligosaccharide-glucose combination and the two oligosaccharide combinations.The results showed that there was no diauxie growth of bifidobacteria in using the above combination,and there were strain differences in the growth generation.Reveal the interspecies cross feeding relationship of bifidobacteria in the utilization of specific carbon sources.By predicting the corresponding substrates of the extracellular enzymes of Bifidobacterium,xylan,2'FL,arabinan,heparin,hyaluronic acid,and chondroitin sulfate were selected for verification.Finally,the combination of xylan and 2'FL and a variety of bifidobacteria was evaluated,which proved that some B.longum strains can cross feeding with B.adolescentis or B.pseudocatenulatum in xylan medium,and cross feeding with B.bifidum in 2'FL.