Department of Earth Sciences, University of Oxford, Oxford, United Kingdom.
Department of Earth Sciences, University of Oxford, Oxford, United Kingdom.
Water Res. 2019 Mar 15;151:98-109. doi: 10.1016/j.watres.2018.11.088. Epub 2018 Dec 19.
Microbes interact with metals and minerals in the environment altering their physical and chemical states, whilst in turn metals and minerals impact on microbial growth, activity and survival. The interactions between bacteria and dissolved chromium in the presence of iron minerals, and their impact on Cr isotope variations, were investigated. Cr(VI) reduction experiments were conducted with two bacteria, Pseudomonas fluorescens LB 300 and Shewanella oneidensis MR-1, in the presence of two iron oxide minerals, goethite and hematite. Both minerals were found to inhibit the rates of Cr(VI) reduction by Pseudomonas, but accelerated those of Shewanella. The Cr isotopic fractionation factors generated by Shewanella were independent of the presence of the minerals (ε = -2.3‰). For Pseudomonas, the ε value was the same in both the presence and absence of goethite (-3.3‰); although, it was much higher (ε = -4.3‰) in the presence of hematite. The presence of aqueous Fe(III) in solution had no detectable impact on either bacterial Cr reduction rates nor isotopic fractionation factors. The presence of aqueous Fe(II) induced rapid abiotic reduction of Cr(VI). The different effects that the presence of Fe minerals had on the Cr fractionation factors and reduction rates of the different bacterial species may be attributed to the way each bacteria attached to the minerals and their different reduction pathways. SEM images confirmed that Pseudomonas cells were much more tightly packed on the mineral surfaces than were Shewanella. The images also confirmed that Shewanella oneidensis MR-1 produced nanowires. The results suggest that the dominant Cr(VI) reduction pathway for Pseudomonas fluorescens LB 300 may have been through membrane-bound enzymes, whilst for Shewanella oneidensis MR-1 it was probably via extracellular electron transfer. Since different minerals impact differentially on bacterial Cr(VI) reduction and isotope fractionation, variations of mineralogies and the associated changes of bacterial communities should be taken into consideration when using Cr isotopes to quantify Cr redox behaviour in the environment.
微生物与环境中的金属和矿物质相互作用，改变它们的物理和化学状态，而金属和矿物质反过来又影响微生物的生长、活性和存活。本研究调查了细菌与溶解态铬在铁矿物存在下的相互作用及其对 Cr 同位素变化的影响。在两种氧化铁矿物 - 针铁矿和赤铁矿的存在下，进行了荧光假单胞菌 LB 300 和希瓦氏菌 MR-1 对 Cr(VI)的还原实验。结果发现，两种矿物都抑制了荧光假单胞菌对 Cr(VI)的还原速率，但加速了希瓦氏菌的还原速率。希瓦氏菌产生的 Cr 同位素分馏因子与矿物的存在无关（ε = -2.3‰）。对于荧光假单胞菌，在针铁矿存在和不存在的情况下，ε 值相同（-3.3‰）；然而，在赤铁矿存在的情况下，ε 值要高得多（ε = -4.3‰）。溶液中存在的水合 Fe(III)对两种细菌的 Cr 还原速率和同位素分馏因子都没有可检测的影响。水合 Fe(II)的存在诱导了 Cr(VI)的快速非生物还原。不同的铁矿物对不同细菌的 Cr 分馏因子和还原速率的影响可能归因于每种细菌与矿物的附着方式及其不同的还原途径。SEM 图像证实，荧光假单胞菌细胞比希瓦氏菌更紧密地附着在矿物表面上。图像还证实了希瓦氏菌 MR-1 产生了纳米线。结果表明，荧光假单胞菌 LB 300 的主导 Cr(VI)还原途径可能是通过膜结合酶，而对于希瓦氏菌 MR-1 可能是通过细胞外电子转移。由于不同的矿物质对细菌 Cr(VI)还原和同位素分馏的影响不同，因此在使用 Cr 同位素量化环境中 Cr 氧化还原行为时，应考虑矿物学的变化以及相关的细菌群落变化。
