Inorganic Polyphosphate, Exopolyphosphatase, and Pho84-Like Transporters May Be Involved in Copper Resistance in Metallosphaera sedula DSM 5348^T

Figure 7

Cartoon working model for copper resistance in M. sedula. In M. sedula DSM 5348^T, copper ions could bind to the transcriptional repressor CopT (Msed_0492) and prevent the binding of this protein to the DNA to activate the transcription of copA (Msed_0490), copT, and copM (Msed_0491) genes. CopM is a possible Cu-binding protein that could sequester copper ions in the cytoplasm. CopA is a putative P-type metal-efflux ATPase that could couple the efflux of copper ions from the cytoplasm and the energy from ATP hydrolysis. On the other hand, PPX (Msed_0891) could hydrolyze PolyP to generate P_i that could complex copper ions. These complexes could be transported outside the cell, together with H⁺ by the H⁺-phosphate symporters, such as the Pho84-like phosphate transporters (Msed_0846, Msed_0866, Msed_1094, and Msed_1512) in both strains DSM 5348^T and CuR1. This last strain has an additional PitA phosphate transporter that could enhance the efflux of complexes and would explain its higher copper resistance. This model is based on the results of the present work and previously reported proposals [8, 9, 11, 13, 19, 29, 34, 35].