Understanding Earth’s past is often the key to understanding our planet’s future. Towards this goal, geochemists use many different tools to study Earth’s climate history. Different tools provide different clues that together help solve the puzzle of what happened in the past. A new set of clues first discovered at the turn of the century (~2000) comes from so called branched tetra ether lipids. Lipids are organic molecules that form the boundary between the inside and outside of cells in all known cellular life including animals, plants, and bacteria. Lipids provide important clues about Earth’s history because they are made by living organisms yet can persist in the environment long after the organism dies. Unlike DNA, sugars and enzymes which tend to break down quickly, some lipids can be preserved in rocks for millennia. This helps uncover at what times in the past different organisms were present. Unfortunately, most lipids do not contain much information about the environment the cell that produced them lived in. This is why the newly discovered tetra ether lipids are of such great scientific interest. These lipids occur in different variations that seem to correspond to the temperature and pH of the environment in which they were formed. In theory, this makes it possible to infer the temperature and pH of past environments. These lipids thus pose a great opportunity to help understand Earth’s climate history. However, it is not known which organisms produce these lipids and why they produce them. This makes it difficult to fully assess how reliable the information is that they can provide about Earth’s past. It also makes it difficult to study what else we could learn from them about Earth’s history. So far it is clear that the organisms that produce them are widespread. These lipids have been found almost everywhere in nature since their discovery 20 years ago. They are twice the size of most plant and animal lipids and are built with stronger chemical bonds. They are especially common in soils and some aspects of their structure suggest they are most likely produced by bacteria. Several types of soil bacteria have been tested in the past decade but no clear source has emerged. The goal of this project is thus to find and study the source of these branched tetra ether lipids by systematically investigating two important reasons they might have gone undetected. First, microbes often produce large organic molecules only when they are needed. Soil bacteria tested in the past might have been prevented from producing these lipids because standard laboratory conditions do not reflect common soil environments. This project will work with a range of soil bacteria in conditions that mimic soil habitats to test this possibility. Second, the bacteria that produce these lipids in the environment might not yet be cultured. To address this possibility, this project will develop a new Course-based Undergraduate Research Experience (CURE). The focus of this CURE will be student-driven isolation and testing of new soil bacteria for these lipids from sites all around Colorado. This CURE will be taught every year at CU Boulder and nearby Red Rocks Community College. In addition, this project will evaluate how undergraduate research experiences impact students’ views on science and interest in science & engineering career paths.
Branched tetraether (brGDGT) lipids are well-preserved, vastly distributed molecular biomarkers with tremendous potential for paleoclimate reconstruction. First described in 2000, brGDGTs are now recognized to exist in virtually all natural environments and their abundance and structural variations are being applied to topics of broad biogeochemical interest. This includes brGDGT-based paleotemperature records that are increasingly used to address fundamental questions in paleoclimate research. However, this rapid expansion has greatly surpassed our fundamental understanding of what brGDGT-based proxies actually represent and how they might have differed in Earth's geologic past. The root of this problem lies with the fact that brGDGTs remain one of the most puzzling "orphaned" biomarkers today. We know little about their biological origins and next to nothing about their biological function. This implies either that potential source organisms cultured to date have not been exposed to the environmental conditions that trigger brGDGT production, or that key source organisms have not yet been cultured or studied in the lab. This projects aims to address both of these possibilities by integrating research and education to advance our understanding of the origins and biological purpose of brGDGTs. The hypothesis that brGDGT production is environmentally induced will be tested using a range of microorganisms that produce potential brGDGT precursor molecules. In particular, the dependence of brGDGT production upon O2, CO2, nutrient flux, and soil microbial interactions will be investigated. The research team will employ chemically static (chemostat) culturing approaches and evaluate the resulting production of brGDGTs and their biosynthetic precursors. The hypothesis that the source organisms of brGDGTs remain uncultured will be pursued by evaluating the production of a brGDGT precursor in bacteria isolated by undergraduate students in a Course Based Undergraduate Research Experience (CURE) class. This class will be developed with a focus on student-driven research into the isolation and study of novel soil bacteria, their metabolites and lipid products. CURE classes provide more inclusive access to early research experiences which are often transformative to students' science identity by increasing self-efficacy and basic research skills. This can lead to increased retention in STEM fields with particularly positive outcomes for first generation and minority students. The development and implementation of the proposed CURE will expose more than 900 undergraduate STEM students to hands-on, cross-disciplinary scientific research practices, collaboration and discovery.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
