COPPER RESISTANCE MECHANISMS IN BACTERIA AND FUNGI

Copper is both an essential micronutrient and a toxic heavy metal for most living cells. The presence of high concentrations of cupric ions in the environment promotes the selection of microorganisms possessing genetic determinants for copper resistance. Several examples of chrom osomal and plasmid copper-resistance systems in bacteria have been rep orted, and the mechanisms of resistance have started to be understood at the molecular level. Bacterial mechanisms of copper resistance are related to reduced copper transport, enhanced efflux of cupric ions, o r copper complexation by cell components. Copper tolerance in fungi ha s also been ascribed to diverse mechanisms involving trapping of the m etal by cell-wall components, altered uptake of copper, extracellular chelation or precipitation by secreted metabolites, and intracellular complexing by metallothioneins and phytochelatins; only the metallothi onein chelation mechanism has been approached with molecular detail.