Metagenomic Approach Study Of Oral Microbiota In Preschool Children Caries

Objective: Metagenomic sequencing was used to analyze the oral microecology of preschool children with caries,and to further study the functional genes of oral microorganism in preschool children,so as to find out the oral microflora and key functional genes related to caries.Methods: The supragingival plaque samples of 80 3-5-year-old children were collected and divided into caries and healthy groups,and then divided into four subgroups according to gender.The DNA was extracted for metagenomic sequencing.Bioinformatics analysis was carried out to comprehensively analyze the gene abundance,microbial composition and function of caries and healthy children.Results:1.Based on the analysis of gene abundanceThe results of Principal Component Analysis(PCA)showed that there was certain difference in gene abundance between healthy children and caries children(P < 0.05).According to gender grouping,PCA and Anosim analysis results showed that gender did not cause the change of gene abundance in the same state.2.General results2.1 Annotation resultsA total of 2,047,955 Open Reading Frames(ORFs)could be annotated to the NR database.About 47 families,57 classes,127 orders,299 families,1,615 genera and12,364 species of bacteria were detected from caries and healthy children.The dominant phyla in preschool children were Actinobacteria,Bacteroidetes,Proteobacteria,Firmicutes,Fusobacteria and Candidayus＿Saccharibacteria.The dominant genera were Actinomyces,Corynebacterium,Capnocytophaga,Neisseria,Prevotella,Streptococcus,Leptotrichia,Veillonella,Selenomonas and Propionibacterium.2.2 Differences in microbial community structure between healthy group and caries groupAt the phylum level,the caries group displayed a higher abundance of Firmicutes and a lower abundance of Proteobacteria than the healthy group.At the genus level,the differences between caries and healthy group were low abundance genus except Neisseria and Veillonella.Veillonella were more abundance in the caries group than in the healthy group,while Neisseria were enriched in the healthy group.At the species level,the number of species belonging to Actinomyces,Streptococcus,Veillonella and Selenomonas in the caries group increased compared with those in healthy group.Neisseria＿lactamica,Neisseria＿mucosa and others were enriched in the healthy group.3.Annotation results of COG,KEGG and CAZy databasesThe results of PCA showed that there were significant differences in the oral microorganism function between the caries group and the healthy group(P < 0.05).The differentially functional genes of oral microorganisms between the two groups were mainly distributed in carbohydrate transport and metabolism and amino acid metabolism.In the caries group,the genes of transcription,carbohydrate transport and metabolism,defense mechanisms,phenylpropanoid biosynthesis,glycosyl transferases and glycoside hydrolases were increased.4.Correlation analysis results of differential functional genes and differential bacteriaSelenomonas＿ruminantium has a strong positive correlation with defense mechanism,phenylpropanoid biosynthesis and glycosyl transferases(P < 0.01),Actinomyces＿urogenitalis and Actinomyces＿graevenitzii were associated with carbohydrate transport and metabolism(P < 0.01).The cariogenic bacteria Streptococcus pyogenes and Streptococcus salivarius were associated with glycosyl transferases(P < 0.01).Conclusion:1.The differences in the composition and function of oral microbial community may be the cause of the occurrence and development of preschool children caries.2.Veillonella＿parvula,Selenomonas＿ruminantium,some Actinomyces and Streptococcus such as Actinomyces＿debtalis,sp＿oral＿taxon＿448,Actinomyces＿urogenitalis,Actinomyces＿graevenitzii,Streptoccus＿oligofermentans,Streptococcus＿cristatus,Streptococcus＿salivarius,Streptococcus＿pyogenes have cariogenic potential.3.Transcriptional functions,carbohydrate transport and metabolism,defense mechanism,phenylpropanoid biosynthesis,glycosyl transferases and glycoside hydrolases synthesis may be related to the occurrence of caries in preschool children.Selenomonas＿ruminantium is closely related to most of the functions,suggesting that it has a strong cariogenic potential.