Dataset Information

Low C/N Ratios Promote Dissimilatory Nitrite Reduction to Ammonium in Pseudomonas putida Y-9 under Aerobic Conditions.

ABSTRACT: The biogeochemical consequences of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) have a significant influence on nitrogen (N) cycling in the ecosystem. Many researchers have explored these two pathways in soil and sediment ecosystems under anaerobic conditions. However, limited information is available regarding the influence of external environmental conditions on these two pathways in a well-defined experimental system under aerobic conditions. In this study, the impacts of the external environmental factors (carbon source, C/N ratio, pH, and dissolved oxygen) on nitrite reduction through the denitrification and DNRA routes in Pseudomonas putida Y-9 were studied. Results found that sodium citrate and sodium acetate favored denitrification and DNRA, respectively. Furthermore, neutral pH and aerobic conditions both facilitated DNRA and denitrification. Especially, low C/N ratios motivated the DNRA while high C/N ratios stimulated the denitrification, which was opposite to the observed phenomena under anaerobic conditions.

SUBMITTER: Huang X

PROVIDER: S-EPMC8305387 | biostudies-literature | 2021 Jul

REPOSITORIES: biostudies-literature

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Low C/N Ratios Promote Dissimilatory Nitrite Reduction to Ammonium in <i>Pseudomonas</i> <i>putida</i> Y-9 under Aerobic Conditions.

Huang Xuejiao X Tie Wenzhou W Xie Deti D Li Zhenlun Z

Microorganisms 20210717 7

The biogeochemical consequences of denitrification and dissimilatory nitrate reduction to ammonium (DNRA) have a significant influence on nitrogen (N) cycling in the ecosystem. Many researchers have explored these two pathways in soil and sediment ecosystems under anaerobic conditions. However, limited information is available regarding the influence of external environmental conditions on these two pathways in a well-defined experimental system under aerobic conditions. In this study, the impac ...[more]

PMID: 34361959

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Project description:Climate change and nutrient pollution are among the most urgent environmental issues. Enhancing the abundance and/or the activity of beneficial organisms is an attractive strategy to counteract these problems. Dissimilatory nitrate reduction to ammonium (DNRA), which theoretically improves nitrogen retention in soils, has been suggested as a microbial process that may be harnessed, especially since many DNRA-catalyzing organisms have been found to possess nosZ genes and the ability to respire N2O. However, the selective advantage that may favor these nosZ-harboring DNRA-catalyzing organisms is not well understood. Here, the effect of N2O on Nrf-mediated DNRA was examined in a soil isolate, Bacillus sp. DNRA2, possessing both nrfA and nosZ genes. The DNRA metabolism of this bacterium was observed in the presence of C2H2, a NosZ inhibitor, with or without N2O, and the results were compared with C2H2-free controls. Cultures were also exposed to repeated oxic-anoxic transitions in the sustained presence of N2O. The NO2--to-NH4+ reduction following oxic-to-anoxic transition was significantly delayed in NosZ-inhibited C2H2-amended cultures, and the inhibition was more pronounced with repeated oxic-anoxic transitions. The possibility of C2H2 involvement was dismissed since the cultures continuously flushed with C2H2/N2 mixed gas after initial oxic incubation did not exhibit a similar delay in DNRA progression as that observed in the culture flushed with N2O-containing gas. The findings suggest a possibility that the oft-observed nosZ presence in DNRA-catalyzing microorganisms secures an early transcription of their DNRA genes by scavenging N2O, thus enhancing their capacity to compete with denitrifiers at oxic-anoxic interfaces. IMPORTANCE Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) is a microbial energy-conserving process that reduces NO3- and/or NO2- to NH4+. Interestingly, DNRA-catalyzing microorganisms possessing nrfA genes are occasionally found harboring nosZ genes encoding nitrous oxide reductases, i.e., the only group of enzymes capable of removing the potent greenhouse gas N2O. Here, through a series of physiological experiments examining DNRA metabolism in one of such microorganisms, Bacillus sp. DNRA2, we have discovered that N2O may delay the transition to DNRA upon an oxic-to-anoxic transition, unless timely removed by the nitrous oxide reductases. These observations suggest a novel explanation as to why some nrfA-possessing microorganisms have retained nosZ genes: to remove N2O that may otherwise interfere with the transition from O2 respiration to DNRA.

Project description:Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox), and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. While the effect of N application on BNF is known, little is known about its effect on NO3- partitioning between DNRA, denitrification, and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox, and BNF and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in a glasshouse with N fertilizer (150 kg N ha-1) and without N fertilizer for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone, but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3- reduced by DNRA (0.42 to 0.52 μg g-1 soil day-1 and 45 to 55%, respectively) were similar to or higher than the amount and proportion reduced by denitrification. However, with N the amount of NO3- reduced by DNRA (0.32 to 0.40 μg g-1 soil day-1) was 40 to 50% lower than the amount of NO3- reduced by denitrification. Denitrification loss increased by >20% with N addition and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02 to 0.25 μg N g-1 soil day-1 We found that DNRA plays a significant positive role in paddy soil N retention, as it accounts for up to 55% of the total NO3- reduction, but this is reduced by N application.IMPORTANCE This study provides evidence that nitrogen addition reduces nitrogen retention through DNRA and increases nitrogen loss via denitrification in a paddy soil ecosystem. DNRA is one of the major NO3- reduction processes, and it can outcompete denitrification in NO3- consumption when rice paddies are low in nitrogen. A significant level of DNRA activity in paddy soils indicates that DNRA plays an important role in retaining nitrogen by reducing NO3- availability for denitrification and leaching. Our study shows that by reducing N addition to rice paddies, there is a positive effect from reduced nitrogen loss but, more importantly, from the conversion of NO3- to NH4+, which is the favored form of mineral nitrogen for plant uptake.

Dataset Information

Low C/N Ratios Promote Dissimilatory Nitrite Reduction to Ammonium in Pseudomonas putida Y-9 under Aerobic Conditions.

Publications

Low C/N Ratios Promote Dissimilatory Nitrite Reduction to Ammonium in <i>Pseudomonas</i> <i>putida</i> Y-9 under Aerobic Conditions.

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