Mn(II) Oxidation Is Catalyzed by Heme Peroxidases in “ Aurantimonas manganoxydans ” Strain SI85-9A1 and Erythrobacter sp. Strain SD-21

ABSTRACT A new type of manganese-oxidizing enzyme has been identified in two alphaproteobacteria, “ Aurantimonas manganoxydans ” strain SI85-9A1 and Erythrobacter sp. strain SD-21. These proteins were identified by tandem mass spectrometry of manganese-oxidizing bands visualized by native polyacrylamide gel electrophoresis in-gel activity assays and fast protein liquid chromatography-purified proteins. Proteins of both alphaproteobacteria contain animal heme peroxidase and hemolysin-type calcium binding domains, with the 350-kDa active Mn-oxidizing protein of A. manganoxydans containing stainable heme. The addition of both Ca 2+ ions and H 2 O 2 to the enriched protein from Aurantimonas increased manganese oxidation activity 5.9-fold, and the highest activity recorded was 700 μM min −1 mg −1 . Mn(II) is oxidized to Mn(IV) via an Mn(III) intermediate, which is consistent with known manganese peroxidase activity in fungi. The Mn-oxidizing protein in Erythrobacter sp. strain SD-21 is 225 kDa and contains only one peroxidase domain with strong homology to the first 2,000 amino acids of the peroxidase protein from A. manganoxydans . The heme peroxidase has tentatively been named MopA (manganese-oxidizing peroxidase) and sheds new light on the molecular mechanism of Mn oxidation in prokaryotes.