Nookongbut Phitthaya, Kantachote Duangporn, Krishnan Kannan, Megharaj Mallavarapu
Faculty of Science, Department of Microbiology, Prince of Songkla University, Hat Yai, Thailand.
Center of Excellence on Hazardous Substance Management (HSM), Bangkok, Thailand.
J Basic Microbiol. 2017 Apr;57(4):316-324. doi: 10.1002/jobm.201600584. Epub 2017 Jan 5.
This study aimed to identify arsenic resistant mechanisms in As-resistant purple nonsulfur bacteria (PNSB) by screening them for presence of As-resistance genes and related enzymes. Resistance to As(III) and As(V) of four As-resistant PNSB determined in terms of median inhibition concentration (IC values) were in the order of strains Rhodopseudomonas palustris C1 > R. palustris AB3 > Rubrivivax benzoatilyticus C31 > R. palustris L28 which corresponded to the presence of As-resistance genes in these bacteria. The strain C1 showed all As-marker genes; arsC, arsM, aioA, and acr3, while aioA was not detected in strain AB3. Strains C31 and L28 had only Arsenite-transporter gene, acr3. Translation of all these detected gene sequences of strain C1 to amino acid sequences showed that these proteins have vicinal cysteine; Cys126, Cys105, and Cys178 of Acr3, ArsC, AioA, respectively. Tertiary structure of proteins Acr3, ArsC, AioA, and ArsM showed strain C1 exhibits the high activities of arsenite oxidase and arsenate reductase enzymes that are encoded by aioA and arsC genes, respectively. Moreover, strain C1 with arsM gene produced volatile-methylated As-compounds; monomethylarsonic acid (MMA), dimethylarsenic acid (DMA), and arsenobetaine (AsB) in the presence of either As(III) or As(V). In conclusion, the strain C1 has great potential for its application in bioremediation of As-contaminated sites.
本研究旨在通过筛选抗砷紫色非硫细菌（PNSB）中抗砷基因和相关酶的存在情况，来确定其抗砷机制。根据半数抑制浓度（IC值）测定的4株抗砷PNSB对As(III)和As(V)的抗性顺序为沼泽红假单胞菌C1菌株＞沼泽红假单胞菌AB3菌株＞苯甲酸红环菌C31菌株＞沼泽红假单胞菌L28菌株，这与这些细菌中抗砷基因的存在情况相对应。C1菌株显示出所有的砷标记基因；arsC、arsM、aioA和acr3，而在AB3菌株中未检测到aioA。C31菌株和L28菌株仅具有亚砷酸盐转运基因acr3。将C1菌株所有这些检测到的基因序列翻译成氨基酸序列表明，这些蛋白质具有相邻的半胱氨酸；分别为Acr3、ArsC、AioA的Cys126、Cys105和Cys178。Acr3、ArsC、AioA和ArsM蛋白的三级结构表明，C1菌株分别表现出由aioA和arsC基因编码的亚砷酸盐氧化酶和砷酸盐还原酶的高活性。此外，具有arsM基因的C1菌株在存在As(III)或As(V)的情况下产生挥发性甲基化砷化合物；一甲基胂酸（MMA）、二甲基胂酸（DMA）和砷甜菜碱（AsB）。总之，C1菌株在砷污染场地的生物修复中具有很大的应用潜力。
