Suenaga Toshikazu, Riya Shohei, Hosomi Masaaki, Terada Akihiko
Department of Chemical Engineering, Tokyo University of Agriculture and Technology, Koganei, Japan.
Front Microbiol. 2018 Apr 10;9:697. doi: 10.3389/fmicb.2018.00697. eCollection 2018.
Nitrous oxide (NO)-reducing bacteria, which reduce NO to nitrogen in the absence of oxygen, are phylogenetically spread throughout various taxa and have a potential role as NO sinks in the environment. However, research on their physiological traits has been limited. In particular, their activities under microaerophilic and aerobic conditions, which severely inhibit NO reduction, remain poorly understood. We used an O and NO micro-respirometric system to compare the NO reduction kinetics of four strains, i.e., two strains of an sp., harboring clade II type , and and , harboring clade I type , in the presence and absence of oxygen. In the absence of oxygen, the highest NO-reducing activity, , was 5.80 ± 1.78 × 10 pmol/h/cell of sp. I13, and the highest and lowest half-saturation constants were 34.8 ± 10.2 μM for and 0.866 ± 0.29 μM for sp. I09. Only sp. I09 showed NO-reducing activity under microaerophilic conditions at oxygen concentrations below 110 μM, although the activity was low (10% of ). This trait is represented by the higher O inhibition coefficient than those of the other strains. The activation rates of NO reductase, which describe the resilience of the NO reduction activity after O exposure, differ for the two strains of sp. (0.319 ± 0.028 h for strain I09 and 0.397 ± 0.064 h for strain I13) and (0.200 ± 0.013 h), suggesting that sp. has a potential for rapid recovery of NO reduction and tolerance against O inhibition. These physiological characteristics of sp. can be of promise for mitigation of NO emission in industrial applications.
一氧化二氮（NO）还原菌在无氧条件下将NO还原为氮气，在系统发育上分布于各种分类群中，在环境中具有作为NO汇的潜在作用。然而，对其生理特性的研究一直有限。特别是，它们在微需氧和有氧条件下的活性，这两种条件会严重抑制NO还原，目前仍知之甚少。我们使用了一个O和NO微呼吸测量系统，比较了四株菌株在有氧和无氧条件下的NO还原动力学，这四株菌株分别是两株携带II类型的某菌属菌株，以及携带I类型的某菌属菌株。在无氧条件下，最高的NO还原活性，即某菌属I13菌株为5.80±1.78×10 pmol/h/细胞，最高和最低的半饱和常数分别为某菌属I13菌株的34.8±10.2μM和某菌属I09菌株的0.866±0.29μM。只有某菌属I09菌株在氧气浓度低于110μM的微需氧条件下表现出NO还原活性，尽管活性较低（为无氧条件下活性的10%）。这一特性表现为其O抑制系数高于其他菌株。描述O暴露后NO还原活性恢复能力的NO还原酶激活率，在某菌属的两株菌株（I09菌株为0.319±0.028 h，I13菌株为0.397±0.064 h）和某菌属菌株（0.200±0.013 h）之间有所不同，这表明某菌属菌株具有NO还原快速恢复和耐受O抑制的潜力。某菌属菌株的这些生理特性有望在工业应用中减少NO排放。
