Effect of hydrogen peroxide on the expression of manganese-oxidizing protein in Erythrobacter sp. SD-21

Understanding the molecular process underlying bacterial manganese (II) oxidation may lead to the development of novel ways to naturally and economically detoxify and restore metal contaminated sites. Several genes involved in bacterial Mn (II) oxidation have been identified. However, little is understood about the regulation of these genes. Recent studies have identified a manganese (II) oxidizing peroxidase (MopA) in α-proteobacterium Erythrobacter sp. SD-21. This novel enzyme has a single animal heme peroxidase domain and seven calcium binding domains. Upstream of the gene encoding MopA (mopA) is an open reading frame encoding a putative transcriptional regulator (mopB). Directly upstream of mopB, a putative promoter and a putative binding site for a hydrogen peroxide responsive regulator, OxyR, was identified. mopB and mopA were found to be on the same transcript. This suggested that MopA expression may be controlled by hydrogen peroxide. The amount of mopA transcript was determined by qPCR using the Pfaffl method with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as the reference gene. mopA expression was down-regulated in the presence of hydrogen peroxide, suggesting its expression may be controlled by the H2O2 responsive regulator, OxyR. However, using an electrophoretic mobility shift assay (EMSA), we were not able to observe a putative OxyR from Erythrobacter sp. SD-21 binding to the OxyR binding site located upstream of mopB and mopA. .