Department of Biology, Nordic Centre for Earth Evolution (Nordcee), University of Southern Denmark, Odense M, Denmark.
Max Planck Institute for Marine Microbiology, Bremen, Germany.
Geobiology. 2017 Nov;15(6):798-816. doi: 10.1111/gbi.12254. Epub 2017 Sep 3.
Anoxygenic phototrophic bacteria utilize ancient metabolic pathways to link sulfur and iron metabolism to the reduction of CO . In meromictic Lake Cadagno, Switzerland, both purple sulfur (PSB) and green sulfur anoxygenic phototrophic bacteria (GSB) dominate the chemocline community and drive the sulfur cycle. PSB and GSB fix carbon utilizing different enzymatic pathways and these fractionate C-isotopes to different extents. Here, these differences in C-isotope fractionation are used to constrain the relative input of various anoxygenic phototrophs to the bulk community C-isotope signal in the chemocline. We sought to determine whether a distinct isotopic signature of GSB and PSB in the chemocline persists in the settling fraction and in the sediment. To answer these questions, we also sought investigated C-isotope fractionation in the water column, settling material, and sediment of Lake Cadagno, compared these values to C-isotope fractionation of isolated anoxygenic phototroph cultures, and took a mass balance approach to investigate relative contributions to the bulk fractionation signature. We found a large C-isotope fractionation between dissolved inorganic carbon (DIC) and particulate organic carbon (POC) in the Lake Cadagno chemocline. This large fractionation between the DIC and POC was also found in culture experiments carried out with anoxygenic phototrophic bacteria isolated from the lake. In the Lake Cadagno chemocline, anoxygenic phototrophic bacteria controlled the bulk C-isotope fractionation, but the influence of GSB and PSB differed with season. Furthermore, the contribution of PSB and GSB to bulk C-isotope fractionation in the chemocline could be traced in the settling fraction and in the sediment. Taken together with other studies, such as lipid biomarker analyzes and investigations of other stratified lakes, these results offer a firmer understanding of diagenetic influences on bacterial biomass.
贫养型光养细菌利用古老的代谢途径将硫代谢和铁代谢与 CO2 的还原联系起来。在瑞士的分层湖 Cadagno 中，紫色硫（PSB）和绿色硫贫养型光养细菌（GSB）都主宰着化变层群落，并驱动硫循环。PSB 和 GSB 通过不同的酶促途径固定碳，并且这些途径在不同程度上分馏 C 同位素。在这里，C 同位素分馏的这些差异被用来约束各种贫养型光养生物对化变层中群落 C 同位素信号的相对输入。我们试图确定化变层中 GSB 和 PSB 的独特同位素特征是否在沉降物和沉积物中持续存在。为了回答这些问题，我们还调查了 Cadagno 湖水柱、沉降物和沉积物中的 C 同位素分馏，将这些值与分离的贫养型光养生物培养物的 C 同位素分馏进行了比较，并采用质量平衡方法研究了对整体分馏特征的相对贡献。我们发现 Cadagno 湖化变层中溶解无机碳（DIC）和颗粒有机碳（POC）之间存在很大的 C 同位素分馏。在与从湖中分离的贫养型光养细菌进行的培养实验中也发现了 DIC 和 POC 之间的这种大分馏。在 Cadagno 湖化变层中，贫养型光养细菌控制着整体 C 同位素分馏，但 GSB 和 PSB 的影响因季节而异。此外，PSB 和 GSB 对化变层中群落 C 同位素分馏的贡献可以在沉降物和沉积物中追踪到。与其他研究（如脂类生物标志物分析和其他分层湖的研究）一起，这些结果提供了对细菌生物量成岩作用影响的更深入理解。
