中文摘要：

采用UV-Vis和HPLC-ICP-MS分析方法,在光照厌氧条件下研究了沼泽红假单胞菌（Rhodopseudomonas palustris CQV97）对砷（As）的抗性和机制.结果表明,As（Ⅴ）与As（Ⅲ）对R.palustris CQV97的半数效应浓度（EC50）分别为2.3mmol·L-1和0.9mmol·L-1;该菌株能够将As（Ⅴ）还原为As（Ⅲ）,不能将As（Ⅲ）转化为As（Ⅴ）或甲基砷;在含有0.1mmol·L-1As（Ⅴ）的培养基中培养80h,细胞积累的总As可达1.32mg·g-1（以干重计）,其中,9.8%存在于细胞质中,4.9%与细胞膜的脂质相结合,其余被认为吸附在细胞表面;全细胞、细胞质、细胞膜所含的As（Ⅲ）和As（Ⅴ）的相对比例分别为16.3%和83.7%、12.1%和87.9%、16.5%和83.5%.静息细胞砷吸附结果表明,与0℃孵育细胞相比,25℃孵育细胞对As（Ⅴ）和As（Ⅲ）吸附量较高;灭活细胞对As（Ⅴ）的吸附量进一步提高,而对As（Ⅲ）的吸附量则降低.因此,光照厌氧条件下,R.palustrisCQV97对As具有较强的抗性和吸附特性,对As（Ⅴ）的抗性和吸附性均明显高于As（Ⅲ）;其抗砷机制为细胞质As（Ⅴ）的还原途径,具体为在细胞内将As（Ⅴ）还原为As（Ⅲ）,继而As（Ⅲ）被转运至细胞外,维持胞内As的含量在较低水平.本研究可为深入理解光合细菌对无机砷的抗性机制、砷的地球化学循环及砷的环境污染和生物修复提供理论参考.

英文摘要：

The arsenic resistance mechanisms of a photosynthetic bacterium, Rhodopseudomonas palustris CQV97, under anaerobic and light conditions, were investigated in this study. It was revealed that the median effective concentration （EC50） of arsenite [As（Ⅲ）] and arsenate [As（Ⅴ）] for this bacterium were 0.9 mmol · L^-1 and 2.3 mmol · L^-1, respectively. In the cells of R. palustris CQV97, As（Ⅴ） could be reduced to As（Ⅲ）, whereas As（Ⅲ） could not be transformed back to As（Ⅴ）. Moreover, the cells lacked arsenic biomethylation ability. When R. palustris CQV97 was exposed to 0.1 mmol · L^-1 As（Ⅴ） for 80 h, 1.32 mg · g^-1 （dry weight） could be accumulated within the cells. Among them, 9.8% was stored in the cytosol, 4.9% was bound to the lipid layer of the cell membrane, the remaining parts were considered to be adsorbed onto the cell surface. The relative proportions of As（Ⅲ） and As（Ⅴ） contained in the whole cell, cytoplasm, and lipid-soluble part were 16.3% and 83.7%, 12.1% and 87.9%, 16.5% and 83.5%, respectively. Analysis of the arsenic adsorption to resting cells revealed a higher adsorption capacity for both As（Ⅲ） and As（Ⅴ） of the cells incubated at 25 ℃ than those at 0 ℃. Furthermore, there was a higher adsorption capacity for As（Ⅴ） of the heat-inactivated cells than the living cells incubated at 25 ℃, and the adsorption capacity for As（Ⅲ） of the heat-inactivated cells was lower than the living cells incubated at 0 ℃. Our results revealed a strong arsenic resistance, and a stronger adsorption ability for As（Ⅴ） than As（Ⅲ） in R. palustris CQV97. In conclusion, this study provides a theoretical reference for an in-depth understanding of the resistance mechanisms of photosynthetic bacteria to inorganic arsenic, the biogeochemical cycles of arsenic, and the potential application of photosynthetic bacteria in bioremediation of arsenic-polluted water.