Microbial reduction of metalloid oxyanions: significance of geochemical factors

背景和原理真菌和细菌是陆地生境中的主要地球活性剂，可以通过还原作用转化Se和Te含氧阴离子，从而降低迁移率和毒性（Gadd，2010年; Gauer等人，2013年）。Se/Te还原似乎是一种广泛发现的性质，并且具有将大量的这些准金属转化为元素Se或Te的潜力（Gadd，1993; Gharieb等，1995），其可以纳米颗粒、纳米晶体和纳米棒形态沉积在细胞内或细胞外（Hockin and Gadd，2003，2006; Oremland et al. 2004; Baesman et al. 2007）。然而，几乎所有的详细研究都是用厌氧的硒酸盐呼吸菌或硫酸盐还原菌进行的（Hockin和Gadd，2003，2006）。令人惊讶的是，几乎没有关于需氧生物体中Se或Te还原的信息，尽管这种能力似乎普遍存在（Gharieb等人，1995）。此外，几乎没有什么是已知的地球化学的影响和限制在有氧栖息地的非金属还原。在土壤或沉积物这样复杂的环境中，在存在多种矿物相、其他氧化还原敏感的金属（类）（例如Fe、As）、不同的营养水平和有机含量以及其他生物体的情况下，类金属还原如何进行？该项目的目的是研究地球化学对需氧微生物还原Se/Te的影响，使用简单到中等复杂性的模型系统，以确定和理解该过程的限制及其重要性。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将被表征，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的细菌-真菌微宇宙和模拟土壤基质。非生物对沉淀的非金属的形式和位置的影响也将被调查。因此，该项目将产生有关有氧Se/Te还原及其意义的基础科学信息，从而增加我们目前对Se/Te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方面的培训，包括相关的分析和制备技术，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）和先进的光学和电子显微镜，X射线元素分析和绘图。

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.