Pseudomonas putida Coordinates the Expression of two Manganese Oxidases and Optimizes Manganese Oxide Precipitation in Response to Aqueous Mn(II)

High Resolution Image Download MS PowerPoint Slide Manganese (Mn) oxides are commonly precipitated by bacteria and fungi. Recent studies have shown that Mn-oxidizing bacteria can harbor multiple Mn oxidases, but environmental controls on the regulation of these enzymes are unknown. Here, we examine the activation of the genes encoding for MnxG and McoA, two Mn oxidases in Pseudomonas putida GB-1, in response to varying Mn(II) concentrations. Using reporter gene fusion strains, we found that mnxG and mcoA are activated only by a fraction of the cells in the population and at different threshold Mn concentrations, with an increasing proportion of cells expressing mnxG (<10 μM) and then mcoA (>10 to 500 μM). Kinetic modeling showed that coexpression of mnxG and mcoA not only alleviates substrate saturation and inhibition of MnxG at high Mn(II) concentrations but also results in an 8-fold increase in the initial rate of Mn oxidation in the wild type compared to strains lacking mnxG or mcoA . The population-level control of gene activation and, ultimately, Mn oxide precipitation, in response to the initial Mn(II) concentration, shows that P. putida fine-tunes the regulation of multiple Mn oxidases to operate under varying environmental conditions.