Mn(II) oxidation in Pseudomonas putida GB-1 is influenced by flagella synthesis and surface substrate

Bacterially mediated manganese(II) oxidation greatly affects the biogeochemical cycling of Mn and other elements. One species of bacteria that are capable of Mn(II) oxidation is the gamma-proteobacterium Pseudomonas putida GB-1. In this organism, Mn(II) oxidation begins in stationary phase on the outer surface of the cell, forming a layer of insoluble Mn(III,IV) oxides. A random transposon mutagenesis screen isolated 12 mutant strains of P. putida GB-1 that exhibited increased Mn(II) oxidation on solid media relative to wild type. In 8 out of the 12 strains, the transposon had inserted into a putative flagellar gene. Those 8 strains each had motility defects, thus the disrupted genes are part of the P. putida GB-1 flagellar regulon. The flagellar genes identified include putative structural components (FliC, FliD, FlgE, and FlgL) and regulatory proteins (FlgM and FleN). Deletion of either the FleN gene (fleN) or the overlapping gene fliA resulted in increased Mn(II) oxidation, while in-frame deletion of fliF, which encodes an essential component of the basal body, did not. In liquid media, the flagellar mutants exhibited delayed Mn(II) oxidation relative to wild type. These results suggest that bacterial Mn(II) oxidation is regulated in part by flagellar-mediated responses to the surface substrate.