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The efficiencies of inorganic mercury bio-methylation by aerobic bacteria under different oxygen concentrations.

机构信息

College of Resources and Environment, Southwest University, Chongqing 400715, China.

Biological Science Research Center of Southwest University, Chongqing 400715, China.

出版信息

Ecotoxicol Environ Saf. 2021 Jan 1;207:111538. doi: 10.1016/j.ecoenv.2020.111538. Epub 2020 Nov 4.

Abstract

Limited information is available about the bio-methylation of inorganic mercury (iHg) under aerobic conditions. In this study, two γ-proteobacteria strains (P. fluorescens TGR-B2 and P. putida TGR-B4) were obtained from the soil of The Three Gorges Reservoir (TGR), demonstrating effective aerobic transformation capacities of iHg into methylmercury (MeHg). Based on periodical changes in soil oxygen content of the TGR, a culture system was established, in which 300 ng Hg (II) L and O were set at 7%, 14%, and 21%, respectively. Results indicated that the two strains differed significantly in bacterial growth rate and MeHg production. The kinetic model of MeHg showed typical characteristics of a "two-staged" process: The first stage was dominated by bio-methylation, which was shown by increasing of net MeHg content. Moreover, the second stage was dominated by bio-demethylation, which decreased net MeHg content. Thus, we hypothesized that the mechanism of aerobic bacterial iHg bio-methylation: (1) should inefficiency compared to anaerobic bacteria i.e.SRB, which were regulated by hgcA/B gene clusters, (2) might be regarded as a passive stress response and depended on the bacterial iHg intoxication threshold and MeHg tolerance threshold.

摘要

有关好氧条件下无机汞(iHg)的生物甲基化的信息有限。在这项研究中,从三峡水库(TGR)的土壤中获得了两株γ-变形菌(荧光假单胞菌 TGR-B2 和恶臭假单胞菌 TGR-B4),它们具有将 iHg 有效转化为甲基汞(MeHg)的好氧转化能力。基于 TGR 土壤中氧含量的周期性变化,建立了一个培养系统,其中 300ng Hg(II)L 和 O 分别设定为 7%、14%和 21%。结果表明,两株菌在细菌生长速率和 MeHg 产量方面存在显著差异。MeHg 的动力学模型表现出典型的“两阶段”过程的特征:第一阶段由生物甲基化主导,表现为净 MeHg 含量的增加。此外,第二阶段由生物脱甲基化主导,净 MeHg 含量减少。因此,我们假设好氧细菌 iHg 生物甲基化的机制:(1)与受 hgcA/B 基因簇调控的厌氧细菌(如 SRB)相比,效率应较低;(2)可能被视为一种被动的应激反应,取决于细菌 iHg 中毒阈值和 MeHg 耐受阈值。

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