SGER: Carbon Isotope Fractionation by Fungal Microorganisms

土壤有机质化石的碳稳定同位素(D13Corg)值在重建关键的古环境特征，如PCO2、d13CO2、植物群落变化和破坏碳循环等过程中起着至关重要的作用。化石d13Corg的价值必须根据微生物分解来理解，在石化过程中，微生物分解会在化学和同位素上改变陆地有机物质。虽然没有细菌那么有名，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。由于这些原因，单细胞真菌在有机质石化过程中提供的碳同位素分馏的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关键的新信息。这位研究人员建议对真菌微生物在富碳介质上生长所产生的碳同位素分馏进行综合表征。这些结果将量化真菌微生物生物学的三个基本方面的同位素分馏：1)碳获取途径；2)社区成长阶段；3.环境温度。这项提案也将4。)研究观察到的碳同位素分馏的生化机制和5。建立真菌特定化合物(即甲壳素和个别脂类，特别是PLFA 18：2-6，9)作为真菌古代谢的同位素指示剂的可能性。基于真菌微生物白色念珠菌和酿酒酵母的初步数据表明，上述每个生物学方面都对生长过程中的碳同位素分馏产生影响，但生物体相对于碳底物的净同位素浓缩一直在1-2%之间。通过对一组不同系统发育的生物体进行一系列扩大的生长实验，这项研究将提出对真菌微生物生长过程中碳同位素分馏的普遍量化，并对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情况进行监测和背景分析。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古指示剂。这项提议将建立与真菌微生物有关的基本碳同位素分馏，并探索将这些想法扩展到地质背景。该项目的结果将为旨在A)的更大的综合建议铺平道路。研究真菌微生物对葡萄糖与简单矿物材料(如二氧化硅)和B。研究酿酒酵母中策略性突变对净葡萄糖代谢途径的影响(包括支持函)。智力优点：拟议的工作将构成真菌微生物碳稳定同位素分馏的详尽表征。这些值将为古环境重建中陆地有机质中d13Corg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因真菌微生物的生长和添加而产生的同位素浓缩，真菌微生物执行陆地生态系统中的大部分碳循环；它还将评估特定化合物在化石记录中反映这种新陈代谢的可能性。更广泛的影响：调查员将继续在每学期与保罗·劳伦斯·邓巴高中和康奈克斯社区领导学院分享她的工作，这两所学校位于市中心，是巴尔的摩的两所弱势公立学校。

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.