Department of Land Resources and Environmental Sciences, Montana State University - Bozeman, Bozeman, MT 59717, USA.
Microbiol Res. 2012 Mar 20;167(3):151-6. doi: 10.1016/j.micres.2011.05.007. Epub 2011 Jul 8.
The ratio of arsenite (As(III)) to arsenate (As(V)) in soils and natural waters is often controlled by the activity of As-transforming microorganisms. Phosphate is a chemical analog to As(V) and, consequently, may competitively inhibit microbial uptake and enzymatic binding of As(V), thus preventing its reduction to the more toxic, mobile, and bioavailable form - As(III). Five As-transforming bacteria isolated either from As-treated soil columns or from As-impacted soils were used to evaluate the effects of phosphate on As(V) reduction and As(III) oxidation. Cultures were initially spiked with various P:As ratios, incubated for approximately 48 h, and analyzed periodically for As(V) and As(III) concentration. Arsenate reduction was inhibited at high P:As ratios and completely suppressed at elevated levels of phosphate (500 and 1,000 μM; P inhibition constant (K(i))∼20-100 μM). While high P:As ratios effectively shut down microbial As(V) reduction, the expression of the arsenate reductase gene (arsC) was not inhibited under these conditions in the As(V)-reducing isolate, Agrobacterium tumefaciens str. 5B. Further, high phosphate ameliorated As(V)-induced cell growth inhibition caused by high (1mM) As pressure. These results indicate that phosphate may inhibit As(V) reduction by impeding As(V) uptake by the cell via phosphate transport systems or by competitively binding to the active site of ArsC.
土壤和天然水中的亚砷酸盐（As(III)）与砷酸盐（As(V)）的比例通常受砷转化微生物的活性控制。磷酸盐是砷酸盐（As(V)）的化学类似物，因此可能会竞争性地抑制微生物对砷酸盐（As(V)）的摄取和酶结合，从而阻止其还原为更具毒性、更易迁移和更具生物利用度的形式 - 亚砷酸盐（As(III)）。从砷处理过的土壤柱或受砷影响的土壤中分离出的 5 种砷转化细菌被用于评估磷酸盐对砷酸盐（As(V)）还原和亚砷酸盐（As(III)）氧化的影响。培养物最初用不同的 P:As 比进行接种，孵育约 48 小时，并定期分析砷酸盐（As(V)）和亚砷酸盐（As(III)）浓度。在高 P:As 比下，砷酸盐（As(V)）还原受到抑制，在高浓度磷酸盐（500 和 1000 μM；磷酸盐抑制常数（K(i））∼20-100 μM）下完全受到抑制。虽然高 P:As 比对微生物砷酸盐（As(V)）还原有明显的抑制作用，但在砷酸盐（As(V)）还原菌根瘤农杆菌 str. 5B 中，这些条件下的砷酸盐（As(V)）还原酶基因（arsC）的表达并未受到抑制。此外，高磷酸盐可缓解高（1mM）砷压力引起的砷酸盐（As(V)）诱导的细胞生长抑制。这些结果表明，磷酸盐可能通过阻碍细胞通过磷酸盐转运系统摄取砷酸盐（As(V)），或通过与 ArsC 的活性位点竞争结合，从而抑制砷酸盐（As(V)）还原。
