Environmental Phylogeny, Physiology, and Evolutionary Significance of Polycyclic Triterpenoids

保存在古代沉积岩中的脂质生物标志物记录是用于解释地球早期环境的基本地球化学工具。 在这个项目中，我们试图更好地了解（i）遗传多样性，（ii）进化历史和（iii）推动这些生物标志物中的一个特定类别（多环三萜类化合物）进化的生理益处。 这些化合物包括类固醇（例如，胆固醇）和类似的微生物化合物称为hopanoids。 该项目将有三个主要组成部分。 我们将通过对hopanoid生物合成的基因进行测序来研究好氧和厌氧环境之间以及陆生和水生系统之间的对比。 我们希望确定这些重要地质生物标志物的主要生物和环境。 我们将研究这些化合物是否赋予一个表型，这是与氧气的存在，通过使用常见的实验室微生物的遗传易处理的菌株。 最后，我们将使用大插入克隆文库来寻找其他种类的三萜环化酶的序列。 这可能有助于我们了解这个基因家族的进化历史。 该项目代表了第一个利用分子生物学方法调查地质生物学感兴趣的主要脂质生物合成途径的系统研究。 我们希望提供有关好氧生物进化、地球表面环境氧化和脂质生物标志物地质记录的新的和可靠的信息。

The record of lipid biomarkers preserved in ancient sedimentary rocks is a fundamental geochemical tool used to decipher early environments on Earth. In this project we seek to achieve a better understanding of the (i) genetic diversity, (ii) evolutionary history and (iii) the physiological benefit that drove the evolution of a particular class of these biomarkers, the polycyclic triterpenoids. These compounds include the steroids (e.g., cholesterol) and the analogous microbial compounds known as hopanoids. This project will have three primary components. We will examine contrasts between aerobic and anaerobic environments and between terrestrial and aquatic system, by sequencing genes for hopanoid biosynthesis. We hope to determine the primary organisms and settings that are sources for these important geological biomarkers. We will study whether these compounds confer a phenotype that is related to the presence of oxygen, by using genetically tractable strains of common laboratory microorganisms. Finally, we will use large-insert clone libraries to look for sequences for other varieties of triterpenoid cyclases. This may help us understand the evolutionary history of this gene family. This project represents the first systematic study to utilize molecular biological approaches to survey a major lipid biosynthetic pathway of interest to geobiology. We hope to provide new and robust information about the evolution of aerobic organisms, oxygenation of Earth surface environments, and the geologic record of lipid biomarkers.