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

¹ The Philips Institute of Oral and Craniofacial Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA
² Department of Microbiology and Immunology, Virginia Commonwealth University, Richmond, VA, USA
³ Department of Biochemistry and Molecular Biology, Virginia Commonwealth University, Richmond, VA, USA
⁴ University of San Luis, San Luis, Argentina

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 cytochrome d ubiquinol oxidase-encoding genes, cydA and cydB, 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 as feoB2, 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. As P. gingivalis is distantly related to the well-studied model organism Escherichia coli, results from our work may provide further understanding of oxygen metabolism and protection in other related bacteria belonging to the phylum Bacteroidetes.

Correspondence
Janina P. Lewis
jplewis{at}vcu.edu

The microarray data discussed in this paper have been deposited in the Gene Expression Omnibus (GEO) repository available at the National Center for Biotechnology Information (NCBI) under the accession number GSE17960.

Four supplementary figures, showing aerobic growth of P. gingivalis W83, a genomic view of the regulated genes, selected pathways affected by the presence of oxygen and the lactate utilization locus, and two supplementary tables, listing genes upregulated and downregulated in bacteria grown in the presence of oxygen, are available with the online version of this paper.