Adaptation of Porphyromonas gingivalis to microaerophilic conditions involves increased consumption of formate and reduced utilization of lactate

Abstract

Porphyromonas gingivalis,previously classified as a strict anaerobe, can grow in the presence of low concentrations of oxygen. Microarray analysis revealed alteration in gene expression in the presence of 6 % oxygen. During the exponential growth phase, 96 genes were upregulated and 79 genes were downregulated 1.4-fold. Genes encoding proteins that play a role in oxidative stress protection were upregulated, including alkyl hydroperoxide reductase (ahpCF), superoxide dismutase (sod) and thiol peroxidase (tpx). Significant changes in gene expression of proteins that mediate oxidative metabolism, such as cytochromedubiquinol oxidase-encoding genes,cydAandcydB, were detected. The expression of genes encoding formate uptake transporter (PG0209) and formate tetrahydrofolate ligase (fhs) was drastically elevated, which indicates that formate metabolism plays a major role under aerobic conditions. The concomitant reduction of expression of a gene encoding the lactate transporter PG1340 suggests decreased utilization of this nutrient. The concentrations of both formate and lactate were assessed in culture supernatants and cells, and they were in agreement with the results obtained at the transcriptional level. Also, genes encoding gingipain protease secretion/maturation regulator (porR) and protease transporter (porT) had reduced expression in the presence of oxygen, which also correlated with reduced protease activities under aerobic conditions. In addition, metal transport was affected, and while iron-uptake genes such as the genes encoding the haemin uptake locus (hmu) were downregulated, expression of manganese transporter genes, such asfeoB2, was elevated in the presence of oxygen. Finally, genes encoding putative regulatory proteins such as extracellular function (ECF) sigma factors as well as small proteins had elevated expression levels in the presence of oxygen. AsP. gingivalisis distantly related to the well-studied model organismEscherichia coli, results from our work may provide further understanding of oxygen metabolism and protection in other related bacteria belonging to the phylumBacteroidetes.