Certain Environmental Conditions Maximize Ammonium Accumulation and Minimize Nitrogen Loss During Nitrate Reduction Process by Pseudomonas putida Y-9.

Xuejiao Huang,Zhenlun Li,Wenzhou Tie,Deti Xie,Daihua Jiang

doi:10.3389/fmicb.2021.764241

Xuejiao Huang, Zhenlun Li + Show 3 more

Open Access

https://doi.org/10.3389/fmicb.2021.764241

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Abstract

Realizing the smallest nitrogen loss is a challenge in the nitrate reduction process. Dissimilatory nitrate reduction to ammonium (DNRA) and nitrate assimilation play crucial roles in nitrogen retention. In this study, the effects of the carbon source, C/N ratio, pH, and dissolved oxygen on the multiple nitrate reduction pathways conducted by Pseudomonas putida Y-9 are explored. Strain Y-9 efficiently removed nitrate (up to 89.79%) with glucose as the sole carbon source, and the nitrogen loss in this system was 15.43%. The total nitrogen decrease and ammonium accumulation at a C/N ratio of 9 were lower than that at 12 and higher than that at 15, respectively (P < 0.05). Besides, neutral and alkaline conditions (pH 7–9) favored nitrate reduction. Largest nitrate removal (81.78%) and minimum nitrogen loss (10.63%) were observed at pH 7. The nitrate removal and ammonium production efficiencies of strain Y-9 increased due to an increased shaking speed. The expression patterns of nirBD (the gene that controls nitrate assimilation and DNRA) in strain Y-9 were similar to ammonium patterns of the tested incubation conditions. In summary, the following conditions facilitated nitrate assimilation and DNRA by strain Y-9, while reducing the denitrification: glucose as the carbon source, a C/N ratio of 9, a pH of 7, and a shaking speed of 150 rpm. Under these conditions, nitrate removal was substantial, and nitrogen loss from the system was minimal.

Highlights

Several environmental factors, including the C/N ratio, oxygen concentration, carbon source, affect enzyme activity in microorganisms by controlling the expression of relevant genes and impacting nitrogen cycles (Szukics et al, 2010; Ke et al, 2013; Caranto and Lancaster, 2017; Yu et al, 2019)
Cells in the logarithmic growth phase were inoculated into a denitrification medium (DM) medium to assess the effects of the carbon source, C/N ratio, pH, and dissolved oxygen (DO) on Y-9–driven NO3− reduction (Li et al, 2019; Yan et al, 2021)
A carbon source is typically essential for the growth of heterotrophic microorganisms, and it acts as an electron donor for nitrogen cycling (Sun et al, 2016)

Summary

INTRODUCTION

Large amounts of industrial fertilizers are often applied to crops to increase crop yields This leads to the considerable accumulation of nitrate (NO3−) in the soil (Kraft et al, 2014). It is clear that DNRA and NO3− assimilation ease the accumulation of NO3− in agricultural soils and improve the efficiency of nitrogen fertilizers. These processes reduce the risk of NO3− loss and mitigate the adverse effects of nitrogen fertilizer use. We speculated that soil NO3− removal could be maximized and soil nitrogen loss could be minimized by adjusting certain external environmental factors to enhance NO3− assimilation and DNRA while decreasing denitrification. We investigate the effects of the carbon source, C/N ratio, pH, and dissolved oxygen (DO) on the accumulation of ammonium in the medium and the expression of nirBD in strain Y-9 during

MATERIALS AND METHODS

Analytical Methods

RESULTS AND DISCUSSION

CONCLUSION

DATA AVAILABILITY STATEMENT