Isolation, characterization, and genetic manipulation of cold-tolerant, manganese-oxidizing <i>Pseudomonas</i> sp. strains

Manganese-oxidizing bacteria (MnOB) produce Mn oxide minerals that can be used by humans for bioremediation, but the purpose for the bacterium is less clear. This study describes the isolation and characterization of cold-tolerant MnOB strains isolated from a compost pile in Morris, Minnesota, USA: <i>Pseudomonas</i> sp. MS-1 and DSV-1. The strains were preliminarily identified as members of species <i>Pseudomonas psychrophila</i> by 16S rRNA analysis and a multi-locus phylogenetic study using a database of 88 genomes from the <i>Pseudomonas</i> genus. However, the average nucleotide identity between these strains and the <i>P. psychrophila</i> sp. CF149 type strain was less than 93%. Thus, the two strains are members of a novel species that diverged from <i>P. psychrophila</i>. DSV-1 and MS-1 are cold tolerant; both grow at 4°C but faster at 24°C. Unlike the mesophilic MnOB <i>P. putida</i> GB-1, both strains are capable of robustly oxidizing Mn at low temperatures. Both DSV-1 and MS-1 genomes contain homologs of several Mn oxidation genes found in <i>P. putida</i> GB-1 (<i>mnxG</i>, <i>mcoA</i>, <i>mnxS1</i>, <i>mnxS2,</i> and <i>mnxR</i>). Random mutagenesis by transposon insertion was successfully performed in both strains and identified genes involved in Mn oxidation that were similar to those found in <i>P. putida</i> GB-1. Our results show that MnOB can be isolated from compost, supporting a role for Mn oxidation in plant waste degradation. The novel isolates <i>Pseudomonas</i> spp. DSV-1 and MS-1 both can oxidize Mn at low temperature and likely employ similar mechanisms and regulation as <i>P. putida</i> GB-1.IMPORTANCEBiogenic Mn oxides have high sorptive capacity and are strong oxidants. These two characteristics make these oxides and the microbes that make them attractive tools for the bioremediation of wastewater and contaminated environments. Identifying MnOB that can be used for bioremediation is an active area of research. As cold-tolerant MnOB, <i>Pseudomonas</i> sp. DSV-1 and MS-1 have the potential to expand the environmental conditions in which biogenic Mn oxide bioremediation can be performed. The similarity of these organisms to the well-characterized MnOB <i>P. putida</i> GB-1 and the ability to manipulate their genomes raise the possibility of modifying them to improve their bioremediation ability.