N(2)O Reduction by Gemmatimonas aurantiaca and Potential Involvement of Gemmatimonadetes Bacteria in N(2)O Reduction in Agricultural Soils

Agricultural soil is the primary N(2)O sink limiting the emission of N(2)O gas into the atmosphere. Although Gemmatimonadetes bacteria are abundant in agricultural soils, limited information is currently available on N(2)O reduction by Gemmatimonadetes bacteria. Therefore, the effects of pH and temperature on N(2)O reduction activities and affinity constants for N(2)O reduction were examined by performing batch experiments using an isolate of Gemmatimonadetes bacteria, Gemmatimonas aurantiaca (NBRC100505(T)). G. aurantiaca reduced N(2)O at pH 5–9 and 4–50°C, with the highest activity being observed at pH 7 and 30°C. The affinity constant of G. aurantiaca cells for N(2)O was 4.4‍ ‍μM. The abundance and diversity of the Gemmatimonadetes 16S rRNA gene and nosZ encoding nitrous oxide reductase in agricultural soil samples were also investigated by quantitative PCR (qPCR) and amplicon sequencing ana­lyses. Four N(2)O-reducing agricultural soil samples were assessed, and the copy numbers of the Gemmatimonadetes 16S rRNA gene (clades G1 and G3), nosZ DNA, and nosZ mRNA were 8.62–9.65×10(8), 5.35–7.15×10(8), and 2.23–4.31×10(9) copies (g dry soil)(–1), respectively. The abundance of the nosZ mRNA of Gemmatimonadetes bacteria and OTU91, OUT332, and OTU122 correlated with the N(2)O reduction rates of the soil samples tested, suggesting N(2)O reduction by Gemmatimonadetes bacteria. Gemmatimonadetes 16S rRNA gene reads affiliated with OTU4572 and OTU3759 were predominant among the soil samples examined, and these Gemmatimonadetes OTUs have been identified in various types of soil samples.