Bioremediation of Cr(Ⅵ) and ammonia is considered as a promising and cost-effective alternative to chemical and physical methods. However, Cr(Ⅵ) could inhibit nitrogen removal by inhibiting intra-/extracellular electron (IET/EET) transfer or nitrifying and denitrifying enzymes activity due to its higher solubility. In this study, we isolated a simultaneous nitrification and denitrification (SND) microorganism Acinetobacter haemolyticus RH19, capable of outcompeting oxygen to take nitrogen oxides/ammonia as electron acceptors, and studied a combined accelerant (cysteine, biotin and cytokinin) to relive the Cr(Ⅵ) stress. Respiratory chain inhibited experiments and intermediates showed that strain RH19 had the intact intracellular respiratory chain. Despite the inhibited complex Ⅳ favoring the electrons transfer to NO_x⁻-N, the SND process was still greatly inhibited with Cr(Ⅵ), likely attributed to lower electron flow to the electron acceptors (nitration/nitrition/denitrification enzyme). Instead, the accelerant detoxified Cr(Ⅵ) mainly at CoQ site responsible for electron transfer to AMO and NAP, as well as complex Ⅳ (related with aerobic denitrification), favoring the shortcut SND (SSND, NH₄⁺-N→NH₂ON→NO₂⁻-N→N₂) process by directly converting nitrite to nitrogen gases. Additionally, accelerant could stimulate the secretion of c-Cyts and flavin mononucleotide (FMN) to improve the electron transfer. Overall, this study highlighted the accelerant-alleviated mechanism in the SND process under Cr(Ⅵ) stress, and deepened the theoretical SND basis for the treatment of co-existing pollutants.

中文翻译：

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减轻 Cr（VI.） 胁迫对溶血性不动杆菌 RH19 同时硝化和反硝化过程的影响


Cr（VI.） 和氨的生物修复被认为是化学和物理方法的一种有前途且具有成本效益的替代方案。然而，Cr（VI.） 由于其较高的溶解度，可以通过抑制细胞内/细胞外电子 （IET/EET） 转移或硝化和反硝化酶活性来抑制氮的去除。在这项研究中，我们分离了一种同时硝化和反硝化 （SND） 微生物溶血性不动杆菌 RH19，它能够超越氧气以氮氧化物/氨作为电子受体，并研究了一种联合促进剂（半胱氨酸、生物素和细胞分裂素）来缓解 Cr（VI.） 应激。呼吸链抑制实验和中间体表明，菌株 RH19 具有完整的细胞内呼吸链。尽管抑制复合物 IV. 有利于电子转移到 NO_x⁻-N，但 Cr（VI.） 仍然极大地抑制了 SND 过程，这可能归因于流向电子受体（硝化/硝化/反化酶）的电子流较低。相反，促进剂主要在 CoQ 位点解毒 Cr（VI.），负责电子转移到 AMO 和 NAP 以及复合物 IV.（与好氧反硝化有关），有利于捷径 SND （SSND，_{NH 4}⁺-N→NH₂ON→NO₂⁻-N→N₂） 工艺，通过将亚硝酸盐直接转化为氮气。此外，促进剂可以刺激 c-Cyts 和黄素单核苷酸 （FMN） 的分泌以改善电子转移。本研究强调了 Cr（VI.） 胁迫下 SND 过程中的促进剂缓解机制，深化了处理共存污染物的 SND 理论基础。