Comparative transcriptomic analysis of Porphyromonas gingivalis biofilm and planktonic cells

Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth.This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.The gram-negative obligate anaerobe Porphyromonas gingivalis, in subgingival dental plaque, has been strongly implicated in the onset and progression of chronic periodontitis, a disease characterized by the destruction of the tooth supporting (periodontal) tissues [1,2]. There is increasing evidence that P. gingivalis is also associated with systemic diseases such as atherosclerosis [3,4] and preterm birth [4]. P. gingivalis is an asaccharolytic organism that relies on the catabolism of amino acids for energy production and growth [5]. An array of virulence factors has been associated with P. gingivalis pathogenicity, including proteases, adhesins, fimbriae and capsular polysaccharide [6,7]. The persistence of P. gingivalis in subgingival plaque for periods sufficiently long enough to elicit disease is inherently dependent on it surviving as part of a mature biofilm. Although mutational analyses have been employed to study genes associated with biofilm development by P. gingivalis [8-14], very little is known about the nature of P. gingivalis physiology and the crucial r