Abstract: Objective： To investigate the characterization of the salivary microbiome in people with obesity and the differences in microbial composition, gene function and metabolic pathways of salivary microbiome between people with obesity and normal weight controls. Methods: The study was carried out in people with obesity and age- and sex-matched normal weight controls. None of these selected participants had the systemic disease, oral mucosal disease or periodontal disease. Unstimulated saliva samples were collected and oral examination was conducted. DNAs from saliva samples were extracted and sequenced in an Illumina NextSeq 500 platform. Community composition, linear discriminant analysis of taxonomic differences，gene prediction, gene set construction and annotation of gene function were performed. Results: The classified bacterial reads of the samples were 2，630，428 for each sample. A total of 11 phyla, 19 classes, 26 orders, 41 families, 62 genera and 164 species were detected ultimately. All samples had the same predominant phyla (Proteobacteria, Firmicutes, Bacteroidetes, Actinobacteria and Fusobacteria). There were statistical differences between the groups at the class, order, family, genus and species levels. At the class level, Negativicutes and Erysipelotrichia were more abundant in the obesity group, while Flavobacteriia and Bateroidetes dominated in normal weight group （P<0.05）. At the species level, 16 showed significant differences in relative abundance among the groups, in which Prevotella melaninogenica，Prevotella salivae，Solobacterium moorei and Atopobium parvulum ware more abundant in the obesity group, whereas Streptococcus sanguinis dominated in normal weight group (P<0.05). The people with obesity had a higher number of salivary microbial genes (P<0.05). We produced statistics on gene prediction and found salivary microbiome of obesity group had a higher number of genes (P < 0.05). Genes associated with the pathways of metabolism and environmental information processing and human diseases were significantly enriched in the saliva samples of people with obesity (P < 0.01). Conclusion: Significant differences were seen in composition, gene function and metabolic pathways of salivary microbiome between people with obesity and normal weight people. We hope to go on further study with larger sample size in the near future.

Key words: Obesity, Oral Microbiome, Saliva, Metagenomics