Comparison of N2O-reducing abilities and genome features of two nosZ-containing denitrifying bacteria, Pseudomonas veronii DM15 and Pseudomonas frederiksbergensis DM22.

Aim: The study systematically compared the N2O-reducing functional performances and the genomic features of two N2O-reducing isolates, aimed to screen out effective N2O-reducing bacteria with strong environmental adaption, and explore the possible regulation.

Methods And Results: Two N2O reducers, namely, Pseudomonas veronii DM15 (DM15) and Pseudomonas frederiksbergensis DM22 (DM22), isolated from paddy soil were selected. Their N2O-reducing abilities, and nosZ gene transcript abundance were determined under different temperatures (20°C, 30°C, 40°C) and oxygen concentrations (0%, 10%, 21%), and the whole genomes were sequenced by Illumina sequencing. The results showed that both DM15 and DM22 exhibited the strongest N2O reducing activity at 30°C and under anaerobic conditions. In comparison, DM15 generally exhibited significantly higher N2O reducing abilities and nosZ gene expression than DM22 under all tested conditions. In addition, DM15 possessed obviously higher expression potentials (codon adaptation index (CAI) value) of nos genes than DM22, and the nos cluster of the former contained a transcriptional regulator gene of dnr, while the latter did not.

Conclusions: The results indicate that DM15 showed obviously stronger N2O-reducing abilities than DM22 under various conditions, which might be closely associated with its dnr transcriptional regulator, and thus promoting the higher transcriptional activities of nos genes. Although anaerobic conditions were the optimal conditions for N2O reduction in both strains, DM15 still reduced a certain amount of N2O even under aerobic conditions.