Manipulation of copper bioavailability in pathogenic bacteria can disrupt metabolism

Abstract

Resistance to traditional antibiotics continues to rise in pathogenic bacteria and the growing worldwide alarm has intensified research within the scientific community seeking alternative antimicrobial therapies. Fundamental to this research is the unravelling of bacterial metabolic pathways to identify proteins susceptible to disruption through either the addition of toxins or the limitation of nutrients and thus reveal novel antimicrobial targets in key pathogens. Copper is an essential micronutrient, required by bacteria as a cofactor in many enzymes, but it can also be toxic when present in excess. Manipulation of the bioavailability and localisation of bacterial copper to create a toxic weapon or to cause nutritional deficiency was explored in pathogenic bacteria through the study of the interactions of copper with key metabolic proteins and with a homologue of a copper storage protein (Csp) that was originally characterised in a strain of Methylosinus trichosporium. Csp1 has been shown to supply copper to the particulate form of methane monooxygenase in a methanotroph, but this copper-enzyme is not found in Neisseria gonorrhoeae, a human pathogen in which a Csp1 homologue has been identified. This organism has undergone extensive genomic reduction, therefore the retention of csp1 suggests a requirement for this protein in this pathogen. In Neisseria gonorrhoeae, potential ‘clients’ for receiving copper from a Csp include metabolic proteins from two alternative respiratory pathways: a nitrite reductase (AniA) and a cbb3 type cytochrome c oxidase (Cco). Using mutant strains of Neisseria gonorrhoeae and manipulation of the copper bioavailability, a growth phenotype was observed in a csp1 knockout, suggesting a role associated with a shift in copper concentration. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), one of the most abundant bacterial metabolic enzymes with a major function in the glycolytic pathway, has been shown to bind copper. Phenotypic investigations of the effect of increasing copper bioavailability in GAPDH-challenged mutants of Staphylococcus aureus showed a weak growth defect, and there was evidence of a change in metabolism, suggesting an increase in copper bioavailability could force the cells to use an alternative energy production pathway; a vulnerability worthy of further exploration.