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.

厌氧光自养细菌利用硫(S)和铁(Fe)作为电子源将二氧化碳固定到生物体中，被认为是地球上最早的生命形式之一，并被研究用于探索矿物-微生物-水圈相互作用的起源。因此，与S和铁循环有关的微生物过程中碳(C)的周转是生命出现和C-Fe-S研究的核心。由于其固碳途径，单个菌株的缺氧光养细菌的碳同位素特征仅被部分研究。重要的是，在微生物的混合群落中，例如在自然系统中，使用了多种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由优势物种决定的，还是由此产生的特征是所有物种的综合。同样，微生物碳周转导致的成岩作用如何影响在水柱、沉积物和最终岩石记录中测量的最终同位素成分也是未知的。建议在西班牙的拉克鲁斯湖和瑞士的卡达尼湖进行实验室和现场实验相结合的方法，以确定缺氧光生体的C同位素特征的保存潜力：1)在没有Fe和S存在的情况下，由于C-固定，以及2)作为分离物和微生物群落中的C-限制，以及3)由于与Fe和S循环有关的微生物碳周转而发生的成岩作用。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。地质碳记录隐藏着有关大气、水圈和地球生命演化的长期问题的关键。对微生物碳同位素分馏特征的分析可能会破译这一碳编年史，并有助于洞察生物体如何塑造地圈，以及地球和其他星球上生命的潜在标志。

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.