Analysis of sequences and classification:
After the assembly of forward and reverse contigs, a total of 2,035,772 sequences were created from 17 samples. Over 99.92% of sequence reads were bacterial and the non-bacterial sequences were removed from the analysis set. After trimming, deduplication and removal of the sequences<420 nt and clustering them at 97% similarity level, there were about 39,097sequences are representative and unique. Bacterial community and composition At different taxonomic levels, the relative abundance of bacterial taxa was assigned to asses if there were any differences in the composition of the bacterial communities. In seventeen oral samples, 27 phyla were detected. Firmicutes was the most predominant phyla across all samples with distribution percentage of 51.1%. Firmicutes phyla were followed by by Proteobacteria, Bacteroidetes, Fusobacteria, Actinobacteria members with (17.24%, 16.53%, 6.12%, and 5.19%, respectively) (Fig. 1). At the family level, community composition of the oral bacteria was more diverse that there were 228 families. The most predominant families were Streptococcaceae, Veillonellaceae, Pasteurellaceae, Neisseriaceae, Prevotellaceae with fraction of ( 26.42%, 16.33%, 8.45%, 7.24%, 6.045%, respectively) . At genu level, there were 636 genera; the most predominant genera were Streptococcus, Veillonella, Prevotella, Neisseria, Haemophilus, Porphyromonas, Fusobacterium and Gamella with fraction of (26.71%, 15.65%, 9.23%, 7.17%, 4.65%, 4.04%, 3.51%, 2.51%, respectively) Core microbiome At genus level, there were 636 genera; relative abundance of the most predominant genera in all samples demonstrates that Streptococcus, Veillonella, Prevotella and Neisseria were the most abundant through the samples (Fig.2). There were 41 genera detected in all the samples, these genera called core genera; core genera defined as the genera that had relative abundance equal or more than 0.1%. Unique genera for a sample defined as the genera that present in just this sample and had relative abundance more than 5% of the total genera.