Environmental Phylogeny, Physiology, and Evolutionary Significance of Polycyclic Triterpenoids

保存在古沉积岩中的脂质生物标志物记录是破译地球早期环境的基本地球化学工具。在这个项目中，我们试图更好地理解(i)遗传多样性，（ii）进化史和（iii）生理上的好处，这些生理上的好处推动了一类特定的生物标志物，多环三萜的进化。这些化合物包括类固醇（如胆固醇）和类似的微生物化合物，称为藿烷类化合物。这个项目将有三个主要组成部分。我们将检查有氧和厌氧环境之间的对比，陆地和水生系统之间，通过测序基因的藿类生物合成。我们希望确定作为这些重要地质生物标志物来源的原始生物和环境。我们将通过使用普通实验室微生物的遗传易感菌株来研究这些化合物是否赋予与氧存在相关的表型。最后，我们将利用大插入克隆文库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史。这个项目代表了第一个系统的研究，利用分子生物学方法来调查一个主要的脂质生物合成途径感兴趣的地理生物学。我们希望为有氧生物的进化、地球表面环境的氧化作用和脂质生物标志物的地质记录提供新的、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.