Suri Navreet, Zhang Yuan, Gieg Lisa M, Ryan M Cathryn
Department of Geoscience, University of Calgary, Calgary, AB, Canada.
Department of Biological Sciences, University of Calgary, Calgary, AB, Canada.
Front Microbiol. 2021 May 5;12:610389. doi: 10.3389/fmicb.2021.610389. eCollection 2021.
Denitrification is a microbial process that converts nitrate (NO ) to N and can play an important role in industrial applications such as souring control and microbially enhanced oil recovery (MEOR). The effectiveness of using NO in souring control depends on the partial reduction of NO to nitrite (NO ) and/or NO while in MEOR complete reduction of NO to N is desired. has been reported as a dominant taxon in such applications, but the impact of NO and NO concentrations, and pH on the kinetics of denitrification by this bacterium is not known. With the goal of better understanding the effects of such parameters on applications such as souring and MEOR, three strains of (K172, NS1 and TK001) were used to study denitrification kinetics when using acetate as an electron donor. At low initial NO concentrations (∼1 mmol L) and at pH 7.5, complete NO reduction by all strains was indicated by non-detectable NO concentrations and near-complete recovery (> 97%) of the initial NO-N as N after 14 days of incubation. The relative rate of denitrification by NS1 was low, 0.071 mmol L d, compared to that of K172 (0.431 mmol L d) and TK001 (0.429 mmol L d). Transient accumulation of up to 0.74 mmol L NO was observed in cultures of NS1 only. Increased initial NO concentrations resulted in the accumulation of elevated concentrations of NO and NO, particularly in incubations with K172 and NS1. Strain TK001 had the most extensive NO reduction under high initial NO concentrations, but still had only ∼78% of the initial NO-N recovered as N after 90 days of incubation. As denitrification proceeded, increased pH substantially reduced denitrification rates when values exceeded ∼ 9. The rate and extent of NO reduction were also affected by NO accumulation, particularly in incubations with K172, where up to more than a 2-fold rate decrease was observed. The decrease in rate was associated with decreased transcript abundances of denitrification genes ( and ) required to produce enzymes for reduction of NO and NO. Conversely, high pH also contributed to the delayed expression of these gene transcripts rather than their abundances in strains NS1 and TK001. Increased NO concentrations, NO levels and high pH appeared to cause higher stress on NS1 than on K172 and TK001 for N production. Collectively, these results indicate that increased pH can alter the kinetics of denitrification by strains used in this study, suggesting that liming could be a way to achieve partial denitrification to promote NO and NO production (e.g., for souring control) while pH buffering would be desirable for achieving complete denitrification to N (e.g., for gas-mediated MEOR).
反硝化作用是一个将硝酸盐（NO₃⁻）转化为N₂的微生物过程，在诸如控制酸化和微生物强化采油（MEOR）等工业应用中可发挥重要作用。在控制酸化中使用NO₃⁻的有效性取决于将NO₃⁻部分还原为亚硝酸盐（NO₂⁻）和/或一氧化氮（NO），而在MEOR中则需要将NO₃⁻完全还原为N₂。已报道[某种细菌]是此类应用中的优势分类群，但NO₃⁻和NO₂⁻浓度以及pH对该细菌反硝化动力学的影响尚不清楚。为了更好地理解这些参数对诸如酸化控制和MEOR等应用的影响，使用了三株[该细菌]（K172、NS1和TK001）来研究以乙酸盐作为电子供体时的反硝化动力学。在低初始NO₃⁻浓度（约1 mmol/L）和pH 7.5条件下，孵育14天后，所有菌株的NO₃⁻均完全还原，表现为未检测到NO₂⁻浓度，且初始NO₃-N以N₂形式近乎完全回收（> 97%）。与K172（0.431 mmol/L·d）和TK001（0.429 mmol/L·d）相比，NS1的反硝化相对速率较低，为0.071 mmol/L·d。仅在NS1培养物中观察到高达0.74 mmol/L的NO₂⁻瞬时积累。初始NO₃⁻浓度增加导致NO₂⁻和NO浓度升高，特别是在K172和NS1的孵育中。在高初始NO₃⁻浓度下，菌株TK001的NO₃⁻还原最为广泛，但孵育90天后，初始NO₃-N以N₂形式回收的仍仅约为78%。随着反硝化作用的进行，当pH值超过约9时，pH升高会显著降低反硝化速率。NO₂⁻还原的速率和程度也受NO₂⁻积累的影响，特别是在K172的孵育中，观察到速率下降超过2倍。速率下降与用于还原NO₂⁻和NO的酶所需的反硝化基因（[具体基因名称1]和[具体基因名称2]）转录丰度降低有关。相反，高pH也导致这些基因转录本在NS1和TK001菌株中的表达延迟而非丰度降低。对于NS1而言，NO₃⁻浓度增加、NO₂⁻水平升高和高pH似乎比K172和TK001对N₂产生造成更大压力。总体而言，这些结果表明，pH升高可改变本研究中使用的[该细菌]菌株的反硝化动力学，这表明加石灰可能是实现部分反硝化以促进NO₂⁻和NO产生（例如用于控制酸化）的一种方法，而pH缓冲对于实现完全反硝化生成N₂（例如用于气体介导的MEOR）是可取的。
