Analysis of C-isotope signatures of iron- and sulfur-metabolizing anoxygenic phototrophic bacteria from modern lakes to understand biogeochemical cycling of carbon, iron and sulfur in ancient environments.

利用硫(S)和铁（Fe）作为电子源将二氧化碳固定到生物质中的无氧光自养细菌被认为是地球上最早的生命形式之一，并被研究用于研究矿物-微生物-水圈相互作用的起源。因此，微生物过程中与S和Fe循环相关的碳(C)的周转是生命和C-Fe-S研究的核心。由于无氧光养生物的碳固定途径，其单个菌株的c同位素特征仅被部分研究。重要的是，在混合的微生物群落中，例如在自然系统中，使用多种c固定途径。目前尚不清楚原位测量的最终c同位素组成是否由一个优势物种决定，还是最终的特征是所有物种的综合。同样，尚不清楚微生物碳转换的成岩作用如何影响水柱、沉积物和岩石记录中测量的最终同位素组成。本文提出在La Cruz（西班牙）和Cadagno（瑞士）模型湖进行实验室和原位实验，以确定缺氧光养动物c同位素特征的保存潜力：1)由于在缺乏和存在Fe和S时的c固定，以及c限制；2)作为分离物和微生物群落；3)成岩作用后由于与Fe和S循环相关的微生物碳转换。这些发现将与目前模拟成岩作用的研究进行比较，因为温度和压力的影响，以及岩石记录调查。地质碳记录是解决有关大气和水圈与地球生命一起进化的持久问题的关键。对微生物c同位素分异特征的分析可能会破解这一碳编年史，并有助于了解生物如何塑造地圈，以及地球和其他行星上生命的潜在标志。

Anoxygenic photoautotrophic bacteria utilizing sulfur (S) and iron (Fe) as electron source to fix carbon dioxide into biomass are considered one of the earliest life forms on earth and are studied to investigate the origins of mineral-microbe-hydrosphere interactions. The turnover of carbon (C) linked to the S and Fe cycle by microbial processes, therefore, lies at the heart of emergence of life and C-Fe-S studies. The C-isotope signatures of individual strains of anoxygenic phototrophs due to their carbon fixation pathways are only partially studied. Importantly, in mixed communities of microorganisms, such as occur in natural systems, multiple C-fixation pathways are used. It is not known whether the final C-isotope composition measured in situ is determined by a dominant species, or whether the resulting signature is an integration of all. Likewise, it is unknown how diagenesis due to microbial carbon turnover influences the final isotopic composition measured in the water column, sediment and finally, the rock record. A combination of laboratory and in situ experiments at model lakes La Cruz (Spain) and Cadagno (Switzerland) are proposed to determine the preservation potential of anoxygenic phototroph C-isotope signatures 1) due to C-fixation in the absence and presence of Fe and S, as well as C-limitation 2) as isolates and in microbial communities, and 3) after diagenesis due to microbial carbon turnover linked to the Fe and S cycles. The findings will be compared to current studies simulating diagenesis due to temperature and pressure influence, as well as rock record investigations. The geological carbon record harbors the key to persistent questions about the evolution of the atmosphere and hydrosphere together with life on earth. Analysis of microbial C-isotope fractionation signatures may decode this carbon chronicle and lend insight to how organisms shape the geosphere, as well as potential markers of life both on earth and other planets.