Comparative gene expression analysis of planktonic Porphyromonas gingivalis ATCC 33277 in the presence of a growing biofilm versus planktonic cells

In this in vitro study, using DNA microarray we investigate the differential gene expression of Porphyromonas gingicalis ATCC 33277 when growing in the presence or in absence of its own monospecies biofilm. P. gingivalis ATCC 33277 cells were grown in modified Brain Heart Infusion medium until obtaining a final concentration of 10^8 colony-forming units per milliliter. This pure culture of P. gingivalis cells was incubated under two conditions within a multi-well culture plate: in the presence or absence of sterile ceramic calcium hydroxyapatite discs. Plates were incubated at 37ºC for 96 hours in anaerobic conditions. The progress was monitored by confocal laser scanning microscopy (CLSM). After incubation, free-floating P. gingivalis cells from both conditions were harvested and total RNA was extracted and purified. Three biological replicates for each condition were independently hybridized for transcriptomic comparisons. Linear model statistics were used to determine the differentially expressed genes in case of a 1.5-fold change (upregulated or downregulated) in gene expression with p-values<0.05. Results were confirmed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR.