硫酸盐还原菌Clostridium sp. BXM对砷的去甲基化及其机制研究

Arsenic (As) is a ubiquitous toxic element in the environment. With the widespread use of organic As in the agriculture and animal husbandry, organic As pollution is becoming more and more serious and cannot be ignored. So far, the study on the mechanism of As transformation focused mostly on the oxidation, reduction and methylation of inorganic As. However, few studies referred to the mechanism of organic As biotransformation, especially in anaerobic microorganisms. Our previous study showed that anaerobic microorganisms played important roles in affecting As species and toxicity. In this project, we will elucidate the mechanism of organic As transformation by sulfate reducing bacterium Clostridium sp. BXM isolated from paddy soil. We will validate the capacity of demethylating monomethylarsonous acid or trivalent roxarsone by Clostridium sp. BXM, as well as the factors affecting this process. We have cloned a potential demethylating gene (arsI) in Clostridium sp. BXM. Further, we will verify the function and regulating mechanism of this gene and characterize the demethylating activity of the encoded protein in vitro. Finally, we want to investigate whether Clostridium sp. BXM can transform organic As into inorganic As in the co-culture system and then affect As species uptake of rice plant through the microcosm experiment. This project will provide some insight into the role of sulfate reducing bacteria in the biogeochemistry of organic As in anaerobic environment, such as the paddy soil. Moreover, they are useful for environmental risk assessment to the abuse of organic As products.

砷是环境中普遍存在的有毒元素。随着农业和畜牧业中有机砷试剂的广泛使用，有机砷带来的砷污染不容忽视。以往有关砷的生物转化机制研究主要集中在无机砷的氧化、还原和甲基化上，对有机砷的生物转化机制研究相对较少，尤其在厌氧菌中更为少见。我们前期的研究表明厌氧微生物对无机砷的形态和毒性有一定调节作用。在本项目中我们针对水稻土中分离的硫酸盐还原菌（Clostridium sp. BXM），首先研究其对甲基砷和洛克沙砷的去甲基化作用及影响因素；已从该菌中克隆到一个可能的砷去甲基化基因arsI，拟进一步鉴定该基因的功能和表达调控机制，同时表征其编码酶的活性；最后，将采用微宇宙模拟试验探讨BXM能否在与水稻共生长环境中通过转化有机砷生成无机砷，从而促进水稻吸收无机砷。本项目将对认识硫酸盐还原菌对稻田等缺氧环境中有机砷生物地球化学循环的作用有指导意义，并且对滥用有机砷制剂的环境风险评估有一定参考作用。

重金属污染目前是全球性的重要环境问题。砷元素是最引人注目的污染重金属之一。砷元素的形态转化过程能够影响其毒性和移动性等，是砷的生物地球化学循环的重要组成部分。环境微生物是砷形态转化的重要驱动因子。在本项目中我们以环境中分布广泛的梭菌属细菌为研究对象，选用菌株Clostridium sp. BXM开展实验，重点关注该菌对砷元素的去甲基化过程，以及该菌内去甲基化关键酶的功能分析。同时，项目又新增了另外一种重金属抗性细菌—Streptomyces cavourensis TJ430的相关重金属研究。该菌能够耐受较高浓度的的无机砷和镉而生长。首先验证了该链霉菌不具备无机砷的甲基化能力。然后通过转录组学等方法初步探寻该菌株可能存在的重金属抗性机制。梭菌属和链霉菌属细菌都在环境中十分普遍，本项目旨在发现两类细菌对重金属砷和镉的抗性机制和转化机制，突出他们在重金属生物地球化学循环中的贡献。