Transcriptome analysis of Porphyromonas gingivalis and Acinetobacter baumannii in polymicrobial communities

Abstract

Acinetobacter baumannii is a nosocomial, opportunistic pathogen that causes several serious conditions including meningitis, septicemia, endocarditis, and pneumonia. It can be found in the oral biofilm, which may be a reservoir for pneumonia and chronic obstructive pulmonary disease. Subgingival colonization by A. baumannii is associated with chronic and aggressive periodontitis as well as refractory periodontal disease. Porphyromonas gingivalis, a keystone periodontal pathogen localized to subgingival plaque, is also implicated in several chronic conditions including aspiration pneumonia. Although both bacteria are found together in subgingival plaque and can cause multiple polymicrobial infections, nothing is known about the interactions between these two important human pathogens. In this study, we used RNA sequencing to understand the transcriptional response of both species as they adapt to heterotypic communities. Among the differentially regulated genes were those encoding a number of important virulence factors for both species including adhesion, biofilm formation, and protein secretion. Additionally, the presence of A. baumannii increased the abundance of P. gingivalis in model dual-species communities. Collectively these results suggest that both P. gingivalis and A. baumannii adapt to each other and have synergistic potential for increased pathogenicity. In identifying the mechanisms that promote pathogenicity and refractory disease, novel approaches to mitigate polymicrobial synergistic interactions may be developed to treat or prevent associated diseases.

Keywords: Acinetobacter baumannii; Porphyromonas gingivalis; RNA-seq; heterotypic communities.

Figure 1. Dot graph of DE genes and functional clusters

Each dot represents the transcriptional response of every ORF numbered sequentially moving from left to right in PgAb vs Pg (left) and PgAb vs Ab (right). The red and green bars represent the significance cutoffs of 0.5 and −0.5 log₂ fold change, respectively.

Figure 2. Differential expression of genes within the phenylacetic acid catabolism pathway in the PgAb communities compared to Ab alone

Results are expressed as log₂ fold change in the PgAb community compared to Ab alone. Higher mRNA levels are represented as red bars and those with no significant change are shown as gray.

Figure 3. Differential expression of adhesins in the PgAb communities

Results are expressed as log₂ fold change in the PgAb community compared to Pg (A) or Ab (B) alone. Higher mRNA levels are represented as red bars, lower levels are represented as green bars and those with no significant change are shown as gray.

Figure 4. Differential expression of Pg TPR domain containing proteins in the PgAb communities

Results are expressed as log₂ fold change in the PgAb community compared to Pg alone. Higher mRNA levels are represented as red bars, lower expression is represented as green bars and those with no significant change are shown as gray.

Figure 5. Ab enhances Pg community development

(A–E) Pg (green) was incubated alone or reacted with a substratum of Ab (red) for 16 h at the cell densities indicated. A series of x-y sections were collected by confocal microscopy and digitally reconstructed into a three-dimensional image. Images are representative of 3 independent experiments. (F) Calculated biovolume of Pg and Ab in the images represented in (A–E) measured using the Volocity software. Results are means with standard deviation of the three experiments. **P<0.01, **** P<0.0001 compared between PgAb and Pg alone using ANOVA with Tukey’s multiple comparison test.