Copper resistance genes of Burkholderia cenocepacia H111 identified by transposon sequencing

Copper is an essential element but in excess is highly toxic and therefore cytoplasmic levels must be tightly controlled. Member of the genus Burkholderia are highly resistant to various heavy metals and are often isolated from acidic soils where copper bioavailability is high. In this study, we employed transposon sequencing (Tn-Seq) to identify copper resistance genes in Burkholderia cenocepacia H111. We identified a copper efflux system that shares similarities with the plasmid-based copper detoxification systems found in Escherichia coli and Pseudomonas syringae. We also found that several of the identified resistance determinants are involved in maintaining the integrity of the cell envelope, suggesting that proteins located in the outer membrane and periplasmic space are particularly sensitive to copper stress. Given that several of the resistance genes are required for the repair and turnover of misfolded proteins, we suggest that copper toxicity is caused by protein damage rather than by oxidative stress.