Dr. Avi Flamholz
Post Doctoral Scholar, Caltech, Newman Lab
Personal Website

Using engineered bacteria to study the history of Earth’s atmosphere

Tuesday, November 12
11:30 AM
AHF 153 (Torrey Webb Room)

Abstract: Microbes are, and have always been, pivotal contributors to the global carbon cycle. Cyanobacteria offer a prime example. Oxygenic photosynthesis via the Calvin cycle is the dominant source of primary productivity on Earth, coupling the oxidation of water (to O2) to the reductive fixation of CO2 into the organics forming all living matter. This key process was “invented” by Cyanobacteria and was only acquired by Eukaryotic algae and plants much later. Yet the Earth is very different today than it was during the Archean eon (>2.5 billion years ago), when Cyanobacteria arose. There is certainly far more O2 in modern atmosphere, and, proxies suggest, far less CO2. Indeed, all modern Cyanobacteria rely on CO2-concentrating mechanisms (CCMs) — complex 15+ gene systems that enable robust growth in environments with low CO2. As I will show, CCMs are entirely dispensable in high CO2 atmospheres (5-10% V/V), indicating that primordial Cyanobacteria would not have needed them. So how did this complex physiology evolve? It is often assumed that long-term decreases in atmospheric CO2 drove the emergence of bacterial CCMs, which are essential for growth in modern atmosphere (≈0.04% CO2). I will describe how we used “synthetic biological” tools to test this hypothesis by constructing present-day analogs of CCM ancestors and assaying their efficacy across a range of CO2 concentrations. The results of these assays delineated viable trajectories for the co-evolution of CCMs with Earth’s atmosphere, supporting geochemical inferences of high paleo-CO2 levels, and contributing to a growing dialogue between microbial physiology, synthetic biology, and Earth science