Cellular and Molecular Biological Approaches to Interpreting Ancient Biomarkers

Our ability to read the molecular fossil record has advanced significantly in the past decade. Improvements in biomarker sampling and quantification methods, expansion of molecular sequence databases, and the application of genetic and cellular biological tools to problems in biomarker research have enabled much of this progress. By way of example, we review how attempts to understand the biological function of 2-methylhopanoids in modern bacteria have changed our interpretation of what their molecular fossils tell us about the early history of life. They were once thought to be biomarkers of cyanobacteria and hence the evolution of oxygenic photosynthesis, but we now believe that 2-methylhopanoid biosynthetic capacity originated in the Alphaproteobacteria, that 2-methylhopanoids are regulated in response to stress, and that hopanoid 2-methylation enhances membrane rigidity. We present a new interpretation of 2-methylhopanes that bridges the gap between studies of the functions of 2-methylhopanoids and their patterns of occurrence in the rock record.

在过去十年中，我们解读分子化石记录的能力有了显著提高。生物标志物采样和定量方法的改进、分子序列数据库的扩充，以及基因和细胞生物学工具在生物标志物研究中的应用，促成了这一进步。例如，我们回顾了在理解现代细菌中2 - 甲基藿烷类化合物的生物学功能方面所做的尝试是如何改变我们对其分子化石所揭示的生命早期历史的解读的。它们曾经被认为是蓝细菌的生物标志物，因此也是产氧光合作用进化的标志，但我们现在认为2 - 甲基藿烷类化合物的生物合成能力起源于α - 变形菌，2 - 甲基藿烷类化合物是受应激反应调控的，并且藿烷的2 - 甲基化会增强膜的刚性。我们对2 - 甲基藿烷提出了一种新的解读，它弥合了2 - 甲基藿烷类化合物功能研究与其在岩石记录中出现模式之间的差距。