Transcriptional Activity of Predominant Streptococcus Species at Multiple Oral Sites Associate With Periodontal Status

Abstract

Background: Streptococcus species are predominant members of the oral microbiota in both health and diseased conditions. The purpose of the present study was to explore if different ecological characteristics, such as oxygen availability and presence of periodontitis, associates with transcriptional activity of predominant members of genus Streptococcus. We tested the hypothesis that genetically closely related Streptococcus species express different transcriptional activities in samples collected from environments with critically different ecological conditions determined by site and inflammatory status.

Methods: Metagenomic and metatranscriptomic data was retrieved from 66 oral samples, subgingival plaque (n=22), tongue scrapings (n=22) and stimulated saliva (n=22) collected from patients with periodontitis (n=11) and orally healthy individuals (n=11). Species-specific transcriptional activity was computed as Log2(RNA/DNA), and transcriptional activity of predominant Streptococcus species was compared between multiple samples collected from different sites in the same individual, and between individuals with different oral health status.

Results: The predominant Streptococcus species were identified with a site-specific colonization pattern of the tongue and the subgingival plaque. A total of 11, 4 and 2 pathways expressed by S. parasanguinis, S. infantis and S. salivarius, respectively, were recorded with significantly higher transcriptional activity in saliva than in tongue biofilm in healthy individuals. In addition, 18 pathways, including pathways involved in synthesis of peptidoglycan, amino acid biosynthesis, glycolysis and purine nucleotide biosynthesis expressed by S. parasanguinis and 3 pathways expressed by S. salivarius were identified with significantly less transcriptional activity in patients with periodontitis.

Conclusion: Data from the present study significantly demonstrates the association of site-specific ecological conditions and presence of periodontitis with transcriptional activity of the predominant Streptococcus species of the oral microbiota. In particular, pathways expressed by S. parasanguinis being involved in peptidoglycan, amino acid biosynthesis, glycolysis, and purine nucleotide biosynthesis were identified to be significantly associated with oral site and/or inflammation status.

Keywords: Streptococcus; metagenomics; metatranscriptomics; oral cavity; periodontitis.

Figure 1

Site-specific distribution of predominant Streptococcus species. Relative abundance of the predominant Streptococcus species in 29 samples (saliva n = 11, subgingival plaque n = 10, tongue biofilm n = 8) in healthy conditions. Color code denotes the percentage read abundance, where light colors indicates increasing abundance and dark colors decreasing abundance.

Figure 2

Overall transcriptional activity of predominant Streptococcus species in oral health. Transcriptional activity of predominant Streptococcus species, as evaluated by log2(RNA/DNA) with each dot representing a specific pathway. (A) Saliva versus tongue biofilm. (B) Saliva versus subgingival plaque. Color coding: red: saliva, blue: tongue biofilm, green: subgingival plaque.

Figure 3

Pathway expression of predominant Streptococcus species in saliva versus tongue biofilm. Pathways identified with significantly different log2(RNA/DNA) in saliva versus tongue biofilm in oral health with each dot representing a specific sample. (A) Streptococcus parasanguinis, (B) Streptococcus infantis, (C) Streptococcus salivarius. Boxplots display first and third quartiles, median. Whiskers display 1.5 * IQR. Color coding: red: saliva, blue: tongue biofilm.

Figure 4

Pathway expression of predominant Streptococcus species in saliva versus subgingival plaque. Pathways identified with significantly different log2(RNA/DNA) in saliva versus subgingival plaque in oral health with each dot representing a specific sample. (A) Streptococcus oralis, (B) Streptococcus sanguinis. Boxplots display first and third quartiles, median. Whiskers display 1.5 * IQR. Color coding: red: saliva, green: subgingival plaque.

Figure 5

Overall transcriptional activity of Streptococcus species in oral health versus periodontitis. Transcriptional activity of predominant Streptococcus species in periodontitis versus oral health, as evaluated by log2(RNA/DNA), with each dot representing a specific pathway. Color coding: yellow: healthy control, grey: periodontitis.

Figure 6

Pathway expression of Streptococcus species in saliva in periodontitis versus oral health. Pathways identified with significantly different log2(RNA/DNA) in saliva from patients with periodontitis versus oral health, with each dot representing a specific sample. (A) Streptococcus parasanguinis, (B) Streptococcus salivarius. Boxplots display first and third quartiles, median. Whiskers display 1.5 * IQR. Color coding: yellow: healthy control, grey: periodontitis.

Figure 7

Pathway expression of Streptococcus species in tongue biofilm in periodontitis versus oral health. Pathways identified with significantly different log2(RNA/DNA) in tongue biofilm from patients with periodontitis versus oral health with each dot representing a specific sample. Streptococcus parasanguinis. Boxplots display first and third quartiles, median. Whiskers display 1.5 * IQR. Color coding: yellow: healthy control, grey: periodontitis.