ABSTRACTThe oxidation of soluble Mn(II) to insoluble Mn(IV) is a widespread bacterial activity found in a diverse array of microbes. In the Mn(II)-oxidizing bacteriumPseudomonas putidaGB-1, two Mn(II) oxidase genes, namedmnxGandmcoA, were previously identified; each encodes a multicopper oxidase (MCO)-type enzyme. Expression of these two genes is positively regulated by the response regulator MnxR. Preliminary investigation into putative additional regulatory pathways suggested that the flagellar regulators FleN and FleQ also regulate Mn(II) oxidase activity; however, it also revealed the presence of a third, previously uncharacterized Mn(II) oxidase activity inP. putidaGB-1. A strain from which both of the Mn(II) oxidase genes andfleQwere deleted exhibited low levels of Mn(II) oxidase activity. The enzyme responsible was genetically and biochemically identified as an animal heme peroxidase (AHP) with domain and sequence similarity to the previously identified Mn(II) oxidase MopA. In the ΔfleQstrain,P. putidaGB-1 MopA is overexpressed and secreted from the cell, where it actively oxidizes Mn. Thus, deletion offleQunmasked a third Mn(II) oxidase activity in this strain. These results provide an example of an Mn(II)-oxidizing bacterium utilizing both MCO and AHP enzymes.IMPORTANCEThe identity of the Mn(II) oxidase enzyme inPseudomonas putidaGB-1 has been a long-standing question in the field of bacterial Mn(II) oxidation. In the current work, we demonstrate thatP. putidaGB-1 employs both the multicopper oxidase- and animal heme peroxidase-mediated pathways for the oxidation of Mn(II), rendering this model organism relevant to the study of both types of Mn(II) oxidase enzymes. The presence of three oxidase enzymes inP. putidaGB-1 deepens the mystery of why microorganisms oxidize Mn(II) while providing the field with the tools necessary to address this question. The initial identification of MopA as a Mn(II) oxidase in this strain required the deletion of FleQ, a regulator involved in both flagellum synthesis and biofilm synthesis inPseudomonas aeruginosa. Therefore, these results are also an important step toward understanding the regulation of Mn(II) oxidation.
Human glyoxalase I. cDNA cloning, expression, and sequence similarity to glyoxalase I from Pseudomonas putida
