Microbial reduction of metalloid oxyanions: significance of geochemical factors

背景与理由真菌和细菌是陆地栖息地中主要的地球活性物质，它们可以通过还原转化Se和Te氧离子，从而降低其流动性和毒性（Gadd, 2010; Glasauer et al. 2013）。硒/碲还原似乎是一种被广泛发现的特性，并且有可能固定大量的这些类金属，如元素硒或碲（Gadd, 1993； Gharieb等人，1995），这些类金属可以在细胞内或细胞外以纳米颗粒、晶体和棒状形态沉积（Hockin和Gadd， 2003, 2006； Oremland等人，2004；Baesman等人，2007）。然而，几乎所有的详细研究都是用厌氧呼吸硒酸盐或硫酸盐还原细菌进行的（Hockin和Gadd， 2003,2006）。令人惊讶的是，尽管好氧生物似乎普遍具有这种能力，但关于硒或硒减少的信息却很少（Gharieb et al. 1995）。此外，对需氧生境中类金属还原的地球化学影响和限制几乎一无所知。在这样一个复杂的环境中，如土壤或沉积物中存在多种矿物相、其他氧化还原敏感金属（类金属），如铁、砷、不同的营养水平和有机含量以及其他生物，类金属如何进行还原？本项目的目的是利用简单到中等复杂程度的模型系统，研究好氧微生物对硒/碲还原的地球化学影响，以确定和了解该过程存在哪些限制及其重要性。将描述其他金属和矿物成分、有机成分和营养物质对地球活性细菌和真菌菌株的类金属还原能力的影响，以及菌株影响其他金属矿物转化的能力。将使用简单的纯培养系统以及混合细菌-真菌微生物和模拟土壤基质。非生物对沉淀类金属的形态和位置的影响也将被研究。因此，该项目将产生关于好氧硒/碲还原及其意义的基础科学信息，从而增加我们目前对硒/碲生物地球化学的理解。该项目将采用跨学科的方法，学生将接受地质微生物学和环境矿物学相关分析和制备技术的培训，包括实验生物的生长和操作，以及原子吸收分光光度法（AAS）、x射线粉末衍射（XRPD）、先进的光学和电子显微镜、x射线元素分析和制图等技术。

Background and rationaleFungi and bacteria are the major geoactive agents in terrestrial habitats and can transform Se and Te oxyanions by reduction, which reduces mobility and toxicity (Gadd, 2010; Glasauer et al. 2013). Se/Te reduction appears to be a widely found property, and has the potential to immobilize substantial amounts of these metalloids as elemental Se or Te (Gadd, 1993; Gharieb et al. 1995) which can be deposited intracellularly or extracellularly in nanoparticulate, -crystalline and -rod morphologies (Hockin and Gadd, 2003, 2006; Oremland et al. 2004; Baesman et al. 2007). However, almost all detailed research has been carried out with anaerobic selenate-respiring or sulfate-reducing bacteria (Hockin and Gadd, 2003, 2006). Surprisingly little information is available for Se or Te reduction in aerobic organisms although the capability seems ubiquitous (Gharieb et al. 1995). Further, almost nothing is known about geochemical influences and limitations on metalloid reduction in aerobic habitats. How can metalloid reduction proceed in such a complex environment as soil or sediment in the presence of multiple mineral phases, other redox-sensitive metal(loid)s, e.g. Fe, As, varying nutrient levels and organic content, and other organisms? WorkplanThe aim of this project is to examine geochemical influence on Se/Te reduction by aerobic microbes, using model systems of simple to intermediate complexity, in order to identify and understand what limitations there are to the process, and their importance. The influence of other metal and mineral components, organic components and nutrients on metalloid reductive capabilities of geoactive bacterial and fungal strains will be characterised, together with the abilities of strains to effect other metal-mineral transformations. Simple pure culture systems as well as mixed bacterial-fungal microcosms and simulated soil matrices will be used. Abiotic influence on the form and location of precipitated metalloids will also be investigated. The project will therefore produce fundamental scientific information regarding aerobic Se/Te reduction and its significance, and therefore add to our current understanding of Se/Te biogeochemistry. This project will use an interdisciplinary approach and the student will receive training in geomicrobiology and environmental mineralogy with associated analytical and preparative techniques, including growth and manipulation of experimental organisms, and techniques including atomic absorption spectrophotometry (AAS), X-ray powder diffraction (XRPD), and advanced light and electron microscopy, X-ray element analysis and mapping.