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.

光合自养细菌是地球上最早的生命形式之一，利用硫（S）和铁（Fe）作为电子源将二氧化碳固定到生物质中，并被用来研究矿物-微生物-水圈相互作用的起源。因此，通过微生物过程与S和Fe循环相关的碳（C）周转是生命出现和C-Fe-S研究的核心。个别菌株的碳同位素签名的缺氧光合生物由于其碳固定途径，只有部分研究。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。目前尚不清楚现场测量的最终碳同位素组成是否由一个占主导地位的物种决定，或者所产生的签名是否是所有的整合。同样，由于微生物碳周转而引起的成岩作用如何影响水柱、沉积物和岩石记录中测得的最终同位素组成也是未知的。 在模型湖拉克鲁斯（西班牙）和卡达尼奥进行的实验室和现场实验相结合的研究（瑞士）提出确定缺氧光养生物C-同位素特征的保存潜力，1）由于在不存在和存在Fe和S的情况下的C-固定，以及C-限制，2）作为分离物和在微生物群落中，3）成岩作用后，微生物碳周转与Fe、S循环有关。这些发现将与目前模拟温度和压力影响的成岩作用的研究以及岩石记录调查进行比较。地质碳记录是解决大气圈、水圈和地球生命演化等长期问题的关键。对微生物碳同位素分馏特征的分析可能会解码这种碳编年史，并深入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.