Projects/Interests

Novel Bacterial System Involved in Copper Tolerance

Copper is an essential trace element required by all aerobic organisms. Copper ions are used as a structural and/or catalytic cofactor in several enzymes (e.g., cytochrome c oxidase and superoxide dismutase). However, free copper ions are highly toxic due to their ability to generate reactive oxygen species, via Fenton-type reactions, which damage lipids, DNA and proteins.

It is crucial for any organism to maintain a tight regulation of the intracellular concentrations of copper ions, a role played by the copper homeostasis systems. Nevertheless, in bacteria as well as in eukaryotic organisms, the molecular mechanisms essential for copper homeostasis are only partially understood. Bacterial systems have been considered as models systems to investigate the mechanism of copper homeostasis, due to their simplicity and easy gene manipulation. In fact, bacterial efflux copper pumps and chaperons are similar to their eukaryotic counterparts.

The study of bacterial copper homeostasis, especially copper tolerance mechanisms, has gain interest due to the widespread use of copper compounds as bactericide in agriculture or as disinfectants in the food industry. This general use will undoubtedly lead to the selection of copper-resistance strains of bacteria and the dissemination of plasmid-borne copper resistance genes among different bacterial pathogens with important implications in disease control efforts. Moreover, mechanisms of copper tolerance have recently been linked to the molecular mechanism of pathogenesis. During infection, bacteria are exposed to different stresses, as reactive oxygen species and fluctuations in metal ions concentration. Indeed, phagocytes infected with Mycobacterium and Salmonella present increased copper levels, that for Mycobacterium tuberculosis, showed to specifically induce the transcription of a gene encoding for a P-type ATPase copper efflux pump. Therefore, there is an increased urge to understand the different bacterial mechanisms of copper tolerance in order to develop new therapeutic targets and improve current copper-based strategies.

Under the scope of copper resistance, we will investigate the molecular mechanism of copper resistance in a bacterial system, Marinobacter hydrocarbonoclasticus, which presents some unique features.

Oxidative Stress Response - Bacterial Cytochrome c Peroxidase

Reactive oxygen species (ROS) (e.g., hydrogen peroxide, superoxide anion) are produced by the immune system to kill invading microorganims. ROS are potent cytotoxic oxidants that can cause damage in the DNA, proteins and lipids, leading to cell damage or death, properties that are exploit by the immune system. Hence, the ability to combat these toxic compounds is fundamental for bacteria survival in the host. Indeed, bacteria have developed a notable array of enzymatic systems for their detoxification, such as superoxide dismutases, catalases and peroxidases.

Recently, it has been shown that cytochrome c peroxidase (CCP) plays a key role in virulence, in pathogenic bacteria, by protecting these microorganims against ROS. In these bacteria, the gene coding for CCP is under the regulation of OxyR, a transcription regulator that responds to increased levels of hydrogen peroxide. In addition, strains of Neisseria with a knock-out in their oxyR or/and ccp gene were shown to be more susceptible to hydrogen peroxide and less virulent.

The CCPs are di-haem c-type enzymes that catalyze the reduction of hydrogen peroxide to water. It is our purpose to isolate the CCPs from the pathogenic bacteria Neisseria gonorrhoeae, as well as the homologous enzyme from Escherichia coli.

Reactive oxygen species like superoxide radical (O2·-), hydrogen peroxide (H2O2), and hydrox