Fe(II) oxidation by metabolically flexible phototrophs under complex geochemical conditions

几十年来的研究表明，环境中铁矿物的微生物形成对全球生物地球化学循环有着至关重要的影响。然而，我们对微生物矿物形成过程的基本理解大多来自微生物纯培养物的实验。通常，这些实验仅用一种非天然高浓度的能量或碳底物进行。然而，在环境中，通常同时存在许多不同来源的底物，而且浓度通常较低。关于铁矿物形成细菌在这些低混合基质条件下的行为存在基本的知识差距。当研究具有高代谢灵活性的微生物类型时，这是一个特别的问题，这些微生物可以使用许多不同的能量和碳源。 在这个项目中，我们提出了一个多学科的方法来确定竞争底物的影响的速率和程度的Fe（II）氧化的代谢最灵活的类型的矿物质形成细菌，缺氧光合Fe（II）氧化剂。 我们的目标是发展一个基本的了解，如何由这些细菌留下的矿物学和生物化学标记物的存在下，而不是铁（即铁（II），醋酸盐，葡萄糖，H2）的影响。为了实现这一目标，我们将广泛地表征各种缺氧光养Fe（II）氧化剂在环境相关的底物浓度（通常在10 s-100 s微米的顺序）的底物偏好。然后，我们将描述这些细菌留下的矿物学和生物化学标记。这将包括使用穆斯堡尔谱、微型反向散射穆斯堡尔谱（MIMOS II）、X射线衍射、共聚焦激光扫描显微镜（CLSM）、低温聚焦离子束扫描电子显微镜（cryo-FIB-SEM）和zeta电位对“矿物指纹”（即矿物和形成的细胞矿物聚集体）进行广泛表征。我们将用蛋白质组学来补充这种矿物学分析，以确定细胞的生物化学在不同的混合基质条件下如何变化。这将使我们能够建立一个环境相关的“分子指纹”的过程中的Fe（II）的氧化。最后，我们将在海洋沉积物微观世界中将这些矿物学和微生物学方法联合收割机结合起来，以确定竞争性底物浓度对发现它们的自然环境中光养Fe（II）氧化活性的影响。最终，矿物学和分子方法的独特组合将提供对Fe（III）控制的透彻理解矿物形成在环境相关的条件下，并开发一套标志物，以确定在自然环境中的光养Fe（II）氧化细菌的贡献。

Decades of previous work have demonstrated that the microbial formation of iron minerals in the environment has a crucial impact on global biogeochemical cycling. However, much of our fundamental understanding of microbial mineral-forming processes comes from experiments with pure cultures of microorganisms. Typically, these experiments are conducted with only one energy or carbon substrate at unnaturally high concentrations. In the environment, however, many different sources of substrate are commonly present at the same time, often with low concentrations. A fundamental knowledge gap exists as to how iron mineral-forming bacteria behave under these low, mixed substrate conditions. This is a particular problem when studying types of microorganisms with high metabolic flexibility which can use many different energy and carbon sources. In this project, we propose a multi-disciplinary approach to determine the effect of competing substrates on rates and extent of Fe(II) oxidation by the most metabolically flexible type of mineral-forming bacteria, anoxygenic phototrophic Fe(II)-oxidizers. We aim to develop a fundamental understanding of how both mineralogical and biochemical markers left by these bacteria are affected by the presence of substrates other than iron (i.e. Fe(II), acetate, glucose, H2). To achieve this, we will extensively characterize the substrate preference of a variety of anoxygenic phototrophic Fe(II)-oxidizers at environmentally relevant substrate concentrations (typically on the order of 10s-100s micrometer). We will then characterize the mineralogical and biochemical markers left by these bacteria. This will include extensive characterization of the “mineral fingerprint” (i.e. minerals and cell-mineral aggregates formed) using Mössbauer spectroscopy, miniaturized backscatter Mössbauer spectroscopy (MIMOS II), X-ray diffraction, confocal laser scanning microscopy (CLSM), cryogenic focussed ion beam scanning electron microscopy (cryo-FIB-SEM) and zeta potentials. We will complement this mineralogical analysis with proteomics to determine how the biochemistry of the cells varies under different mixed substrate conditions. This will enable us to establish an environmentally-relevant “molecular fingerprint” for the process of Fe(II) oxidation. Finally, we will combine both these mineralogical and microbiological approaches in marine sediment microcosms in order to determine the effect of competing substrate concentration on the activity of phototrophic Fe(II) oxidation in one of the natural environments in which they are found. Ultimately this unique combination of mineralogical and molecular approaches will provide a thorough understanding of the controls on Fe(III) mineral formation at environmentally relevant conditions, and develop a suite of markers with which to identify the contribution of phototrophic Fe(II)-oxidizing bacteria in the natural environment.