Camacho Antonio, Walter Xavier A, Picazo Antonio, Zopfi Jakob
Cavanilles Institute for Biodiversity and Evolutionary Biology, University of Valencia Burjassot, Spain.
Bristol BioEnergy Centre, Bristol Robotics Laboratory, University of the West of England Bristol, UK.
Front Microbiol. 2017 Mar 21;8:323. doi: 10.3389/fmicb.2017.00323. eCollection 2017.
Photoferrotrophy, the process by which inorganic carbon is fixed into organic matter using light as an energy source and reduced iron [Fe(II)] as an electron donor, has been proposed as one of the oldest photoautotrophic metabolisms on Earth. Under the iron-rich (ferruginous) but sulfide poor conditions dominating the Archean ocean, this type of metabolism could have accounted for most of the primary production in the photic zone. Here we review the current knowledge of biogeochemical, microbial and phylogenetic aspects of photoferrotrophy, and evaluate the ecological significance of this process in ancient and modern environments. From the ferruginous conditions that prevailed during most of the Archean, the ancient ocean evolved toward euxinic (anoxic and sulfide rich) conditions and, finally, much after the advent of oxygenic photosynthesis, to a predominantly oxic environment. Under these new conditions photoferrotrophs lost importance as primary producers, and now photoferrotrophy remains as a vestige of a formerly relevant photosynthetic process. Apart from the geological record and other biogeochemical markers, modern environments resembling the redox conditions of these ancient oceans can offer insights into the past significance of photoferrotrophy and help to explain how this metabolism operated as an important source of organic carbon for the early biosphere. Iron-rich meromictic (permanently stratified) lakes can be considered as modern analogs of the ancient Archean ocean, as they present anoxic ferruginous water columns where light can still be available at the chemocline, thus offering suitable niches for photoferrotrophs. A few bacterial strains of purple bacteria as well as of green sulfur bacteria have been shown to possess photoferrotrophic capacities, and hence, could thrive in these modern Archean ocean analogs. Studies addressing the occurrence and the biogeochemical significance of photoferrotrophy in ferruginous environments have been conducted so far in lakes Matano, Pavin, La Cruz, and the Kabuno Bay of Lake Kivu. To date, only in the latter two lakes a biogeochemical role of photoferrotrophs has been confirmed. In this review we critically summarize the current knowledge on iron-driven photosynthesis, as a remains of ancient Earth biogeochemistry.
光铁营养作用是一种利用光能作为能源、以还原态铁[Fe(II)]作为电子供体将无机碳固定为有机物的过程，被认为是地球上最古老的光合自养代谢方式之一。在太古宙海洋以富铁（铁质）但贫硫化物为主导的条件下，这种代谢方式可能在光合层的初级生产中占据了大部分份额。在此，我们综述了目前关于光铁营养作用的生物地球化学、微生物学和系统发育方面的知识，并评估了这一过程在古代和现代环境中的生态意义。从太古宙大部分时间盛行的铁质条件来看，古代海洋逐渐演变为缺氧富硫化物（缺氧且富含硫化物）的环境，最终，在有氧光合作用出现很久之后，又演变成了以有氧环境为主的状态。在这些新条件下，光铁营养生物作为初级生产者的重要性逐渐降低，如今光铁营养作用仅作为一种曾经重要的光合过程的遗迹而存在。除了地质记录和其他生物地球化学标志物外，类似于这些古代海洋氧化还原条件的现代环境能够让我们深入了解光铁营养作用在过去的重要性，并有助于解释这种代谢方式如何作为早期生物圈有机碳的重要来源发挥作用。富含铁的半咸水湖（永久分层）可被视为古代太古宙海洋的现代类似物，因为它们具有缺氧的铁质水柱，在化学跃层处仍有光照，从而为光铁营养生物提供了适宜的生态位。已证实少数紫色细菌菌株以及绿硫细菌菌株具有光铁营养能力，因此能够在这些现代太古宙海洋类似物中繁衍生息。到目前为止，已在马塔诺湖、帕万湖、拉克鲁斯湖以及基伍湖的卡布诺湾开展了关于光铁营养作用在铁质环境中的发生情况及其生物地球化学意义的研究。迄今为止，只有在后两个湖泊中证实了光铁营养生物的生物地球化学作用。在本综述中，我们批判性地总结了目前关于铁驱动光合作用的知识，它是古代地球生物地球化学的遗留物。
