Abstract:

Arsenic, a strong carcinogenic and toxic metalloid element, widely exists in the natural water environment. The reduction of As (V) by microorganisms to As (III) enhances arsenic mobility, toxicity, and environmental risks. Under aerobic conditions, attention was given to microbial arsenic oxidation. However, there was a lack of quantitative research on how dissolved oxygen concentration affects the arsenic reduction in arsenic-resistant microorganisms. In this study, Aeromonas hydrophila HS01 was selected due to its various environmental functions. Previous studies have proved that it has the function of anaerobic iron reduction, nitrate reduction, azo dye decolorization and DDT biodegradation. Through genome sequencing analysis, this strain had the arsenic carrier protein gene of arsB and the intracellular arsenic reduction gene of arsC, which indicated that A. hydrophila HS01 was capable of reducing As (V). In arsenic reduction microcosmic reaction system, the arsenic reduction kinetics of A. hydrophila HS01 under different electron donors and different oxygen concentrations conditions revealed that its reduction ability was significantly regulated by oxygen. Under various electron donor conditions, there was no significant reduction of As (III) in anaerobic environment. Under the condition of micro-aerobic environment (297 μg·L^-1), the arsenic reduction rate constant reached 0.09/d, and the reaction rate was about 25.3 μM·d^-1. With the increase of dissolved oxygen concentration, the arsenic reduction rate reached the maximum in the system with an oxygen concentration of 414 μg·L^-1 and the rate constant of 1.46/d. The results of functional gene RNA quantitative PCR showed that the expression of arsenic reduction genes first increased and then decreased with the increase of dissolved oxygen concentration, which was similar with the trend of arsenic reduction rate. There was a significant positive correlation between gene expression and rate constant, indicating that oxygen regulated the expression of functional genes and then affected arsenic reduction rate. In this study, the arsenic reduction ability of A. hydrophila HS01 was determined and was regulated by oxygen, which could provide a theoretical basis for understanding the transformation of arsenic in aerobic and micro-aerobic environments, and also provide a theoretical support for arsenic risk prevention.

Key words: arsenic, Aeromonas hydrophila, arsenic resistance, oxygen, gene expression, arsC, arsB

摘要：

砷是一种强致癌有毒类金属元素，广泛存在于自然水体环境之中。微生物还原As(V)产生As(III)，可致使砷移动性增强，毒性升高，环境风险增加。前期有氧条件下的报道中，研究者更多关注微生物砷氧化，但对于溶氧浓度如何影响砷抗性微生物的砷还原缺乏定量研究。嗜水气单胞菌HS01（Aeromonas hydrophila HS01）为该文研究团队分离得到的一株具有系列环境功能的菌种，前期已证明其包含厌氧铁还原、硝酸盐还原、偶氮染料还原脱色、DDT生物转化等能力。选取其为研究对象，通过基因组测序分析，确定了该菌具有arsB砷载体蛋白基因和arsC胞内砷还原基因，明确了它的砷还原功能；通过构建砷还原微宇宙反应体系，解析了不同电子供体、不同氧气浓度条件下嗜水气单胞菌HS01的砷还原动力学，发现其砷还原能力受氧气调控显著。在该研究使用的多种电子供体条件下，嗜水气单胞菌HS01均不能在厌氧环境中还原产生As(III)。而微氧（297 μg·L^-1）条件下，砷还原速率常数达到0.09/d，反应速率约25.3 μmol·L^-1·d^-1；随溶氧浓度增加，砷还原速率在氧含量为414 μg·L^-1的体系中达到最大值，速率常数达到1.46/d。功能基因RNA定量结果显示，砷还原基因的表达量随溶氧浓度升高而先增后降，其趋势与砷还原速率一致，基因表达与速率常数之间呈显著正相关关系，预示着氧气调控了功能基因的表达进而影响砷的还原速率。该研究确定了嗜水气单胞菌HS01的砷还原功能，明确了氧气对其砷还原能力的调控规律，可为理解有氧与微氧水体环境中砷的转化提供理论依据，也将为砷的风险防控提供理论支持。

关键词: 砷, 嗜水气单胞菌, 砷抗性, 氧气, 基因表达, arsC, arsB