Isolation and Characterization of Pseudomonas Strains Capable of Fe(III) Reduction with Reference to Redox Response Regulator Genes

Abstract

Two bacterial strains, KNA-6-3 and KNA-6-5, were isolated from groundwater of the Tono uranium mine, Gifu Prefecture, central Japan, and showed slight but persistent ferric iron (Fe(III)) reduction. The 16S rDNA sequences of the strains were > 96% similar to that of the facultative denitrifier Pseudomonas stutzeri, a species that has not been regarded as a reducer of Fe(III). The genes of redox stress response regulators involved in switching between aerobic and anaerobic metabolisms, arcA, arcB and anr, were amplified by PCR and sequenced. Phylogenetic analyses of the amplified sequences showed high similarities to known arcA, arcB and anr genes from other bacterial species. Expression of the putative arcA, arcB and anr genes was monitored by real-time reverse transcription PCR during aerobic and anaerobic growth. Transcripts of the putative arcA and anr increased with slight but persistent Fe(III) reduction, whereas the putative arcB transcript showed no significant correlation with Fe(III) reduction. The putative anr sequences from the two strains were less similar, and therefore the putative arcA sequences were targeted to estimate the abundance of related bacteria in the Tono uranium mine groundwater. Real-time genomic PCR using universal arcA primers and an arcA probe showed that arcA-bearers would occur at as low as 0.06% (50 cells ml−1) of the total microbial population of 8.05 × 104 cells ml−1.