The Gram-positive bacteria Enterococcus hirae, Lactococcus lactis, and Bacillus subtilis have received wide attention in the study of copper homeostasis. Consequently, copper extrusion by ATPases, gene regulation by copper, and intracellular copper chaperoning are understood in some detail. This has provided profound insight into basic principles of how organisms handle copper. It also emerged that many bacterial species may not require copper for life, making copper homeostatic systems pure defense mechanisms. Structural work on copper homeostatic proteins has given insight into copper coordination and bonding and has started to give molecular insight into copper handling in biological systems. Finally, recent biochemical work has shed new light on the mechanism of copper toxicity, which may not primarily be mediated by reactive oxygen radicals.

Bacteria are rapidly killed on copper surfaces. However, the mechanism of this process remains unclear. Using Enterococcus hirae, the effect of inactivation of copper homeostatic genes and of medium compositions on survival and copper dissolution was tested. The results support a role for dissolved copper ions in killing.

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Background: ␣-Proteobacteria, extant relatives of mitochondria, are model organisms for studying assembly of bacterial and mitochondrial metalloenzymes. Results: Periplasmic thioredoxin TlpA is a specific reductant for copper chaperone ScoI and cytochrome oxidase subunit II (CoxB). Conclusion: Cysteines in the copper-binding sites of ScoI and CoxB must be reduced prior to metallation. Significance: Structures of TlpA-ScoI and TlpA-CoxB intermediates reveal mechanistic details of the reduction process.