The research interests of my laboratory are focused on genetic and biochemical analyses of Gram-positive bacterial physiology, and their application to elucidating mechanisms by which bacterial pathogens cause disease. Our primary focus is the toxin producing bacterial species Corynebacterium diphtheriae. As well as being a toxigenic human pathogen C. diphtheriae also serves as a model organism for the study of iron-dependent gene regulation in Gram-positive and acid-fast bacterial species. The diphtheria toxin repressor DtxR is the primary iron-responsive transcriptional regulator in C. diphtheriae and regulators homologous to DtxR are found in many bacterial species (including the pathogenic Mycobacteria). Interestingly a protein similar to the ferric uptake regulator Fur is also found in C. diphtheriae and we are currently analyzing its role in gene regulation. We are investigating the role(s) of DtxR and the Fur-like regulator in controlling metal ion uptake and homeostasis as well as oxidative stress protection systems.
The metabolism of iron and protection from the deleterious effects of reactive oxygen species are irretrievably linked. Iron is an essential cofactor for many enzymatic reactions. However under oxidizing conditions iron is available to participate in the Fenton reaction, resulting in highly reactive species capable of causing damage to cellular components.
Fe2+ + H2O2 ----> Fe3+ + .OH + OH-
Fe3+ + H2O2 ----> Fe2+ + .OOH + H+
Illuminating the mechanisms that protect C. diphtheriae from reactive oxygen species will likely provide information on possible mechanisms by which C. diphtheriae evades those host defenses that rely on causing oxidative damage and may reveal new targets for the development of antimicrobial agents active against many Gram positive bacterial pathogens.
In addition to our work with C. diphtheriae we have expanded our focus to include iron and oxidative stress dependent gene regulation in the Gram positive nosicomial pathogen Enterococcus faecalis. Hospital acquired E. faecalis strains are often resistant to multiple antibiotics and in addition these strains serve as a reservoir of antibiotic resistance genes that can be transferred to other bacterial pathogens. New methods to treat and prevent infection by E. faecalis are sorely needed. E. faecalis encodes proteins with homology both to DtxR and Fur and little is currently known about the function of these proteins. Our goals are to characterize the role of these proteins in pathogenesis of and gene regulation in E. faecalis and thereby to provide new targets for the development of antimicrobials.
Oram, D. M, Jacobson, A. D. and R. K. Holmes. Transcription of the Contiguous sigB, dtxR and galE Genes in Corynebacterium diphtheriae: Evidence for Multiple Transcripts and Regulation by Environmental Factors 2006 J Bacteriol. 188(8): 2959-2973