Investigating the roles of Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles in the survival of early cyanobacteria and photoferrotrophic bacteria

生命在近40亿年前在地球上进化，但围绕其进化的环境条件仍然知之甚少。古老的微生物化石和同位素记录表明，在3.5Ga之前，存在着蓬勃发展的光合作用微生物生态系统，可能最早在3.8Ga。然而，这些环境呈现出高水平的紫外线辐射和有毒的铁浓度，这应该会使早期的海洋环境不适合生命。古代光合作用细菌(光养铁细菌和蓝藻)如何克服这些环境压力的答案可能在于太古宙海水本身的组成。2.5Ga以前的海水中二氧化硅丰度高，通过在古水柱中形成Fe(II)-硅酸盐和Fe(III)-硅酸盐络合物和纳米颗粒，可能有助于古代光合作用细菌的最初生存，以及沿海海洋环境的早期殖民。这些复合体和纳米颗粒不仅起到了抵御高水平入射紫外线辐射的‘防晒霜’的作用。通过与铁(II)络合，二氧化硅将把溶解的、可生物利用的和有毒的铁(II)的水平降低到更易管理的水平，从而使早期细菌能够在高铁条件下生存和进化。在这方面，这项建议的目的有两个：i)确定Fe(II)-硅酸盐和Fe(III)-硅酸盐络合物和纳米颗粒的地球化学组成和物理性质，以及ii)确定它们保护自由漂浮(浮游)蓝藻和光铁营养生物免受太古代紫外线辐射的能力。通过将从太古宙岩石记录中获得的信息应用于地球化学和生物模型，这种多学科的方法将有助于阐明早期水岩和大气以及早期生命之间的一些重要相互作用。

Life evolved on Earth nearly four billion years ago, but the environmental conditions surrounding its evolution remains poorly understood. Ancient microbial fossil and isotopic records indicate the existence of thriving photosynthetic microbial ecosystems by 3.5 Ga, and perhaps as early as 3.8 Ga. However, these environments presented high levels of UV radiation and toxic iron concentrations that should have made early marine environments inhospitable to life. The answer to how ancient photosynthetic bacteria (photoferrotrophs and cyanobacteria) overcame these environmental stresses possibly lies in the composition of Archean seawater itself. High silica abundances in pre-2.5 Ga seawater may have been instrumental in the initial survival of ancient photosynthetic bacteria, as well as to the early colonization of littoral marine environments, by forming Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles in the ancient water column. These complexes and nanoparticles would have not only acted as a ‘sunscreen’ against the high levels in incident UV radiation. By complexing with iron(II), silica would have lowered the level of dissolved, bioavailable and toxic iron(II) to more manageable levels, thus enabling the survival and evolution of early bacteria under high iron conditions. In this regard, the purpose of this proposal is twofold: i) to identify the geochemical composition and physical nature of the Fe(II)-silicate and Fe(III)-silicate complexes and nanoparticles, and ii) to determine their ability at protecting free-floating (planktonic) cyanobacteria and photoferrotrophs from long-term exposure to Archean-level UV radiation. By applying information derived from the Archean rock record, to geochemical and biological models, this multidisciplinary approach will allow the elucidation of a number of important interactions between the early hydro-litho- and atmosphere, and early life.