微生物对砷的氧化还原竞争

Competitive Microbial Oxidation and Reduction of Arsenic

滤池被广泛运用于饮用水厂中,前期研究发现某水厂生物滤池处理含砷地下水时,一方面三价砷可被生物氧化锰氧化为五价砷,另一方面滤池系统中存在的微生物砷还原酶可促使五价砷还原为三价砷,而滤池表面存在的这种微生物竞争关系会影响滤池的稳定性及处理效率.为探讨其内在机制,本研究选取1株锰氧化模式菌(Pseudomonas sp.QJX-1)和1株砷还原模式菌(Brevibacterium sp.LSJ-9),考察在Mn2+、As(As3+、As5+)共存时,两菌株对空间、营养物质以及对砷氧化/还原的竞争关系.结果表明,不同的反应时间,Mn、As质量浓度/价态不同,三价及五价砷体系中,Pseudomonas sp.QJX-1生成的锰氧化物在砷的氧化还原反应中占主导地位,即能迅速氧化本身存在的As3+(三价砷体系)和砷还原菌产生的As3+(五价砷体系),最终两体系中砷都主要以As5+的形式存在.PCR及RT-PCR结果表明,反应过程中锰氧化菌功能基因(cum A)抑制了砷还原酶(ars C)的表达,锰氧化菌16S rRNA表达量始终比砷还原菌高两个数量级,即锰氧化菌在生长竞争过程中占优势.实验结果表明滤池的水力停留时间是决定出水中砷价态的一个重要因素.

Filters are widely applied in drinking water treatment plants. Our previous study,which explored the asenic redox in a filter of drinking water plant treating underground water,found that As3 ＋could be oxidized to As5 ＋by biogenic manganese oxides,while As5 ＋could be reduced to As3 ＋by some microbial arsenic reductases in the biofilter system. This microbial competition could influence the system stability and treatment efficiency. To explore its mechanism,this study selected a manganese-oxidizing bacterial strain（ Pseudomonas sp. QJX-1） and a arsenic-reducing strain（ Brevibacterium sp. LSJ-9） to investigate their competitive relationship in nutrient acquisition and arsenic redox in the presence of Mn2 ＋,As3 ＋or As5 ＋. The results revealed that the concentration and valence of Mn and As varied with different reaction time; biological manganese oxides dominated the arsenic redox by rapidly oxidizing the As3 ＋in the existing system and the As3 ＋generated by arsenic reductase into As5 ＋. PCR and RT-PCR results indicated that the arsenic reductase（ ars C） was inhibited by the manganese oxidase（ cum A）. The expression of 16 S rRNA in QJX-1 was two orders of magnitude higher than that in LSJ-9,which implied QJX-1 was dominant in the bacterial growth. Our data revealed that hydraulic retention time was critical to the valence of arsenic in the effluent of filter in drinking water treatment plant.