School of Civil and Environmental Engineering, Cornell University, Ithaca, New York, USA.
Department of Biology, University of Ottawagrid.28046.38, Ottawa, Ontario, Canada.
Appl Environ Microbiol. 2022 Aug 23;88(16):e0089122. doi: 10.1128/aem.00891-22. Epub 2022 Aug 1.
Microbe-mediated transformations of arsenic (As) often require As to be taken up into cells prior to enzymatic reaction. Despite the importance of these microbial reactions for As speciation and toxicity, understanding of how As bioavailability and uptake are regulated by aspects of extracellular water chemistry, notably dissolved organic matter (DOM), remains limited. Whole-cell biosensors utilizing fluorescent proteins are increasingly used for high-throughput quantification of the bioavailable fraction of As in water. Here, we present a mathematical framework for interpreting the time series of biosensor fluorescence as a measure of As uptake kinetics, which we used to evaluate the effects of different forms of DOM on uptake of trivalent arsenite. We found that thiol-containing organic compounds significantly inhibited uptake of arsenite into cells, possibly through the formation of aqueous complexes between arsenite and thiol ligands. While there was no evidence for competitive interactions between arsenite and low-molecular-weight neutral molecules (urea, glycine, and glyceraldehyde) for uptake through the aquaglyceroporin channel GlpF, which mediates transport of arsenite across cell membranes, there was evidence that labile DOM fractions may inhibit arsenite uptake through a catabolite repression-like mechanism. The observation of significant inhibition of arsenite uptake at DOM/As ratios commonly encountered in wetland pore waters suggests that DOM may be an important control on the microbial uptake of arsenite in the environment, with aspects of DOM quality playing an important role in the extent of inhibition. The speciation and toxicity of arsenic in environments like rice paddy soils and groundwater aquifers are controlled by microbe-mediated reactions. These reactions often require As to be taken up into cells prior to enzymatic reaction, but there is limited understanding of how microbial arsenic uptake is affected by variations in water chemistry. In this study, we explored the effect of dissolved organic matter (DOM) quantity and quality on microbial As uptake, with a focus on the role of thiol functional groups that are well known to form aqueous complexes with arsenic. We developed a quantitative framework for interpreting fluorescence time series from whole-cell biosensors and used this technique to evaluate effects of DOM on the rates of microbial arsenic uptake. We show that thiol-containing compounds significantly decrease rates of As uptake into microbial cells at environmentally relevant DOM/As ratios, revealing the importance of DOM quality in regulating arsenic uptake, and subsequent biotransformation, in the environment.
微生物介导的砷（As）转化通常需要在酶反应之前将砷吸收到细胞内。尽管这些微生物反应对于砷的形态和毒性非常重要，但对于细胞外水化学，特别是溶解有机物质（DOM）如何调节砷的生物利用度和吸收的理解仍然有限。利用荧光蛋白的全细胞生物传感器越来越多地用于高通量定量水中砷的生物可利用部分。在这里，我们提出了一种解释生物传感器荧光时间序列作为砷吸收动力学测量的数学框架，我们用它来评估不同形式的 DOM 对三价亚砷酸盐吸收的影响。我们发现，含巯基的有机化合物显著抑制了亚砷酸盐进入细胞的吸收，这可能是由于亚砷酸盐和巯基配体之间形成了水相配合物。虽然没有证据表明亚砷酸盐和低分子量中性分子（尿素、甘氨酸和甘油醛）之间存在竞争相互作用，因为它们通过 aquaglyceroporin 通道 GlpF 进入细胞，GlpF 介导了细胞膜内亚砷酸盐的转运，但有证据表明，不稳定的 DOM 部分可能通过类似分解代谢物抑制的机制抑制亚砷酸盐的吸收。在湿地孔隙水中常见的 DOM/As 比观察到亚砷酸盐吸收的显著抑制表明，DOM 可能是环境中微生物摄取亚砷酸盐的重要控制因素，DOM 质量的各个方面在抑制程度中起着重要作用。 稻田土壤和地下水含水层等环境中砷的形态和毒性受微生物介导的反应控制。这些反应通常需要在酶反应之前将砷吸收到细胞内，但对于水化学变化如何影响微生物砷吸收的了解有限。在这项研究中，我们探讨了溶解有机物质（DOM）数量和质量对微生物砷吸收的影响，重点研究了众所周知的与砷形成水相配合物的巯基功能团的作用。我们开发了一种定量框架来解释全细胞生物传感器的荧光时间序列，并使用该技术评估 DOM 对微生物砷吸收速率的影响。我们表明，在环境相关的 DOM/As 比下，含巯基的化合物会显著降低亚砷酸盐进入微生物细胞的吸收速率，这表明 DOM 质量在调节环境中砷的吸收以及随后的生物转化方面具有重要意义。
