Bradyrhizobium ottawaense efficiently reduces nitrous oxide through high nosZ gene expression

Abstract

N2O is an important greenhouse gas influencing global warming, and agricultural land is the predominant (anthropogenic) source of N2O emissions. Here, we report the high N2O-reducing activity of Bradyrhizobium ottawaense, suggesting the potential for efficiently mitigating N2O emission from agricultural lands. Among the 15 B. ottawaense isolates examined, the N2O-reducing activities of most (13) strains were approximately five-fold higher than that of Bradyrhizobium diazoefficiens USDA110T under anaerobic conditions. This robust N2O-reducing activity of B. ottawaense was confirmed by N2O reductase (NosZ) protein levels and by mitigation of N2O emitted by nodule decomposition in laboratory system. While the NosZ of B. ottawaense and B. diazoefficiens showed high homology, nosZ gene expression in B. ottawaense was over 150-fold higher than that in B. diazoefficiens USDA110T, suggesting the high N2O-reducing activity of B. ottawaense is achieved by high nos expression. Furthermore, we examined the nos operon transcription start sites and found that, unlike B. diazoefficiens, B. ottawaense has two transcription start sites under N2O-respiring conditions, which may contribute to the high nosZ expression. Our study indicates the potential of B. ottawaense for effective N2O reduction and unique regulation of nos gene expression towards the high performance of N2O mitigation in the soil.

Bradyrhizobium ontarionense sp. nov., a novel bacterial symbiont isolated from Aeschynomene indica (Indian jointvetch), harbours photosynthesis, nitrogen fixation and nitrous oxide (N2O) reductase genes

“…The nosZ gene has been detected infrequently in the rhizobia and has been found only in strains of the symbiotic species B. diazoefficiens (Sameshima-Saito et al 2006 ; Itakura et al 2013 ; Akiyama et al 2016 ), B. ottawaense (Wasai-Hara et al 2020a , b ), Ensifer meliloti (Bueno, et al 2015 ) and Rhizobium leguminosarum (Hénault et al 2022 ). Recently nosZ gene containing strains of the nitrogen-fixing soybean symbiont, B. ottawaense , were found to be highly efficient with regard to the reduction of N 2 O to inert dinitrogen gas and the use of these strains as inoculants was suggested as a strategy for mitigating N 2 O emissions from agricultural soils (Wasai-Hara et al 2023 ). In the current study we detected key genes encoding enzymes required for the complete denitrification of nitrate or nitrite to nitrogen gas in the genome sequence of strain A19 T as follows: napEDABC (nitrate reductase); nirK (nitrite reductase); norCBQDE (nitric oxide reductase) and nosRZDFYLX (nitrous oxide reductase).…”

Microbial community composition and Co-occurrence network analysis of the rhizosphere soil of the main constructive tree species in Helan Mountain of Northwest China

“…Tomentella and Hebeloma are negatively correlated with Cortinarius, Helvella, and Sebacina, possibly because they are all ectomycorrhizal fungi with similar functions, which leads to their competition for ecological niches. Bradyrizobiaceae, Nitrosomonadaceae, and Acidimimicrobiaceae all may promote nitrogen cycling in ecosystems 52,53 . Pseudonocardiaceae and Nocardioidaceae can participate in the decomposition and cycling of organic matter, thereby promoting vegetation growth 54 .…”

Complete genome sequence of Bradyrhizobium ottawaense strain MIAE 01942 isolated from soybean nodules grown in antibiotic-amended soil

“…Phylogenetic analysis based on multilocus sequence typing, 16S rRNA gene and intergenic spacer sequencing, identified the bacterium as a strain of Bradyrhizobium ottawaense (designated strain MIAE 01942) ( 3 ). Importantly, this species has great potential for N 2 O mitigation in agricultural soils, owing to the high expression levels of an N 2 O reductase (encoded by nosZ ) ( 4 ). Here, we report the complete genome sequence of B. ottawaense strain MIAE 01942.…”