Laboratory of Microbiology, Institute of Biology, University of Neuchâtel Neuchâtel, Switzerland ; Faculty of Environment and Technology, Bristol BioEnergy Centre, University of the West of England Bristol, UK.
Department of Microbiology and Ecology, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain.
Front Microbiol. 2014 Dec 8;5:713. doi: 10.3389/fmicb.2014.00713. eCollection 2014.
Precambrian Banded Iron Formation (BIF) deposition was conventionally attributed to the precipitation of iron-oxides resulting from the abiotic reaction of ferrous iron (Fe(II)) with photosynthetically produced oxygen. Earliest traces of oxygen date from 2.7 Ga, thus raising questions as to what may have caused BIF precipitation before oxygenic photosynthesis evolved. The discovery of anoxygenic phototrophic bacteria thriving through the oxidation of Fe(II) has provided support for a biological origin for some BIFs, but despite reports suggesting that anoxygenic phototrophs may oxidize Fe(II) in the environment, a model ecosystem of an ancient ocean where they are demonstrably active was lacking. Here we show that anoxygenic phototrophic bacteria contribute to Fe(II) oxidation in the water column of the ferruginous sulfate-poor, meromictic lake La Cruz (Spain). We observed in-situ photoferrotrophic activity through stimulation of phototrophic carbon uptake in the presence of Fe(II), and determined light-dependent Fe(II)-oxidation by the natural chemocline microbiota. Moreover, a photoferrotrophic bacterium most closely related to Chlorobium ferrooxidans was enriched from the ferruginous water column. Our study for the first time demonstrates a direct link between anoxygenic photoferrotrophy and the anoxic precipitation of Fe(III)-oxides in a ferruginous water column, providing a plausible mechanism for the bacterial origin of BIFs before the advent of free oxygen. However, photoferrotrophs represent only a minor fraction of the anoxygenic phototrophic community with the majority apparently thriving by sulfur cycling, despite the very low sulfur content in the ferruginous chemocline of Lake La Cruz.
前寒武纪条带状铁建造（BIF）的沉积传统上归因于亚铁（Fe(II)）与光合作用产生的氧气之间的非生物反应导致的铁氧化物的沉淀。最早的氧气痕迹可以追溯到 27 亿年前，这就提出了在产氧光合作用出现之前，可能是什么导致了 BIF 的沉淀的问题。好氧光合细菌通过氧化 Fe(II)而大量繁殖的发现为一些 BIF 的生物起源提供了支持，但尽管有报道表明，好氧光合细菌可能会在环境中氧化 Fe(II)，但缺乏一个可证明它们在其中活动的古代海洋缺氧光养生物的模型生态系统。在这里，我们表明，缺氧光合细菌有助于贫硫酸盐、分层的铁氧化硫湖拉克鲁斯（西班牙）水层中 Fe(II)的氧化。我们通过在存在 Fe(II)的情况下刺激光养碳摄取来观察到原位光亚铁营养活性，并通过自然化学层微生物区系确定了光依赖性 Fe(II)氧化。此外，从富铁水层中富集到与绿菌属铁氧化菌最密切相关的光亚铁营养细菌。我们的研究首次证明了在贫铁水层中，缺氧光亚铁营养与缺氧 Fe(III)-氧化物沉淀之间的直接联系，为在自由氧出现之前 BIF 的细菌起源提供了一个合理的机制。然而，光亚铁营养细菌仅代表了缺氧光养生物群落的一小部分，尽管拉克鲁斯湖的富铁化学层中的硫含量非常低，但大部分显然通过硫循环而大量繁殖。
