SGER: Carbon Isotope Fractionation by Fungal Microorganisms

土壤有机质化石（SOM）碳稳定同位素（d13Corg）值是重建土壤pCO2、d13CO2、植物群落变化、碳循环中断等关键古环境特征的重要输入。化石d13Corg值必须从微生物分解的角度来理解，微生物分解在石化过程中以化学和同位素的方式转化了陆相有机质。虽然没有细菌那么出名，但单细胞真菌负责植物和动物产生的大部分碳的陆地循环。因此，单细胞真菌在SOM化石过程中传递的碳同位素分异方向和可能的大小将为化石SOM d13Corg值的解释以及古环境重建提供重要的新信息。研究者建议全面表征真菌微生物在富碳培养基上生长所产生的碳同位素分馏法。这些结果将量化真菌微生物生物学三个基本方面的同位素分馏：1)碳获取途径；2)群落生长期；3)环境温度。本研究还将4.)研究观察到的碳同位素分异的生化机制；5.)建立真菌特异性化合物（即几丁质和单个脂质，特别是PLFA 18:2-6,9）作为真菌古代谢同位素指标的潜力。基于真菌微生物白色梭菌和酿酒梭菌的初步数据表明，上述每一个生物方面都对生长过程中的碳同位素分异产生影响，但生物体相对于碳底物的净同位素富集始终在1 - 2%之间。通过对一组系统发育上多样化的生物体进行扩展的生长实验，本研究将提出真菌微生物生长过程中碳同位素分馏的广义量化，在微生物生物学的基本方面进行测试。培养研究将根据我们对生化细胞合成的观察进行监测和背景化。该项目还将评估从真菌微生物细胞壁中提取的特定化合物作为潜在的d13C古指示物。这一建议将建立与真菌微生物相关的基本碳同位素分馏，并探索将这些想法扩展到地质环境。该项目的结果将为更大的整合提案铺平道路，旨在a)检查真菌微生物对葡萄糖与简单矿物材料（例如二氧化硅）的代谢，以及b)检查酿酒酵母的策略突变对净葡萄糖代谢途径的影响（包括支持信）。知识价值：提出的工作将构成真菌微生物的碳稳定同位素分馏的详尽表征。这些数值将为古环境重建中陆相有机质d13g的一般解释提供一个关键框架。特别是，它将量化土壤有机质中由真菌微生物的生长和添加而产生的同位素富集，真菌微生物在陆地生态系统中执行大部分碳循环；它还将评估化石记录中反映这种代谢的特定化合物的潜力。更广泛的影响：调查员将继续每学期与Paul Laurence Dunbar高中和ConneXions社区领导学院分享她的工作，这两所巴尔的摩市中心的弱势公立学校。

The carbon stable isotope (d13Corg) value of fossilized soil organic matter (SOM) is a crucial input during the reconstruction of key paleoenvironmental characteristics, such as pCO2, d13CO2, changes in plant community, and disruption of the carbon cycle. Fossil d13Corg values must be understood in terms of microbial decomposition, which transforms terrestrial organic materials both chemically and isotopically during the fossilization process. Although less celebrated than bacteria, it is the unicellular fungi that are responsible for the terrestrial cycling of most of the carbon produced by plants and animals. For these reasons, the direction and possible magnitude of carbon isotope fractionation imparted by unicellular fungi during the fossilization of SOM will form a critical new piece of information for the interpretation of fossil SOM d13Corg values, and by extension, for paleoenvironmental reconstructions. The investigator proposes to comprehensively characterize the carbon isotope fractionation resulting from the growth of fungal microorganisms on a carbon-rich medium. These results will quantify isotopic fractionation across three fundamental aspects of fungal microorganism biology: 1.) carbon acquisition pathway; 2.) community growth-phase; 3.) environmental temperature. This proposal will also 4.) investigate the biochemical mechanisms of observed carbon-isotope fractionation and 5.) establish the potential for fungal specific compounds (i.e., chitin and individual lipids, especially PLFA 18:2-6,9) to be used as isotopic indicators of fungal paleometabolism.Preliminary data based on the fungal microorganisms C. albicans and S. cerevisiae suggest that each of the above biological aspects exert an influence on carbon isotope fractionation during growth, and yet net isotopic enrichment of the organism relative to the carbon substrate consistently falls between 1 - 2 per cent. By performing an expanded set of growth experiments on a phylogenetically diverse group of organisms, this study will present a generalized quantification of carbon isotope fractionation during the growth of fungal microorganisms, tested across fundamental aspects of microbial biology. The cultures studies will be monitored and contextualized in terms of our observations of biochemical cell synthesis. The project will also evaluate the specific compounds extracted from fungal microorganism cell walls as potential d13C paleoindicators in their own respect. This proposal will establish the fundamental carbon isotope fractionations associated with fungal microorganisms and explore the extension of these ideas to the geological setting. The results of this project will pave the way for a larger integrative proposals intended to A.) examine fungal microorganism metabolism of glucose complexed with simple mineral materials (e.g., silica), and B.) examine the effects of strategic mutation in S. cerevisiae upon net glucose metabolic pathway (letter of support included).Intellectual Merit: the proposed work will constitute an exhaustive characterization of carbon stable isotope fractionation of fungal microorganisms. These values will introduce a key framework for the general interpretation of d13Corg in terrestrial organic matter forpaleoenvironmental reconstruction. In particular, it will quantify the isotopic enrichment in soil organic matter that stems from the growth and addition of fungal microorganisms, which perform most of the carbon cycling in terrestrial ecosystems; it will also evaluate the potential for specific compounds to reflect this metabolism in the fossil record. Broader Impacts: The investigator will continue to share her work each semester with Paul Laurence Dunbar High School and ConneXions Community Leadership Academy, two inner-city disadvantaged Baltimore Public Schools.