SGER: Isolation of a Photoferrotrophic Bacterium from Iron Enriched Environments

将寻找一种光铁营养细菌(进行光合作用并使用亚铁作为还原剂的细菌)。这种生物体是一种假想的趋光性生物，是放氧光系统II反应中心进化中缺失的一环。蓝藻和远缘关系较远的紫细菌和柔线菌的苯醌类反应中心。反应中心多肽序列的巨大差异和还原电位的巨大差距，从而决定了还原剂的性质用于这些远亲生物体的光合作用表明可能存在一个或多个进化的有机体光合作用的中间产物。这种光化学氧化铁的中间生物体可以解释太古宙中氧化铁在氧化光合作用出现之前的地球化学现象。虽然中间生物在反应中心的进化史上可能已经存在，但它们今天可能已经灭绝。因此，本研究具有探索性和高风险性。已经确定了合适的环境，并将仔细分析可能维持光铁营养的微生境的存在。这些环境包括富铁的酸性矿山排水区、铁泉和浅层富铁湖泊的沉积物。微生境将通过使用微电极来寻找缺氧微区，这些微区暴露在光下，富含亚铁，低硫化物，以及中性或酸性的pH。一旦找到合适的微生境，将收集样本进行显微镜检查、色素含量和培养，试图分离出一种富铁光生细菌。

A photoferrotrophic bacterium (one that does photosynthesis and uses ferrous iron as a reductant) will be sought. This organism is a hypothetical phototroph that is a missing link in the evolution of the oxygen-evolving photosystem II reaction center in cyanobacteria and the distantly related quinone type reaction centers of the purple bacteria and Chloroflexus. Large differences in the sequences of the reaction center polypeptides and large gaps in the reduction potentials and hence the nature of reductants used for photosynthesis in these distantly related organisms suggest the probable existence of one or more organisms that were evolutionary intermediates in photosynthesis. Such an intermediate organism that photochemically oxidized iron would explain the geochemical appearance of oxidized iron in the Archean eon before the advent of oxygenic photosynthesis. Although intermediate organisms may have existed in the evolutionary history of the reaction center, they may be extinct today. Consequently this research is exploratory and high risk in nature. Suitable environments have been identified and will be carefully analyzed for the presence of microhabitats the could sustain photoferrrotrophy. These environments include iron-rich acid mine drainage areas, iron springs, and the sediments of shallow iron rich lakes. The microhabitats will be sought by using microelectrodes to find anoxic microzones that are exposed to light and that are high in ferrous iron, low in sulfide, and of neutral or acidic pH. Once suitable microhabitats have been found, samples will be collected for microscopy, pigment content, and culture to attempt to isolate a photoferrotroph.