Seminar: Philip Donoghue, 4th March 2024

The nature of the Last Universal Common Ancestor and its impact on the early Earth system

Philip Donoghue

University of Bristol

Monday, March 4th 2024, 1PM ETC/5PM UTC

Livestream at: https://go.wisc.edu/72uniz

Abstract

The nature of the Last Universal Common Ancestor (LUCA), its age, and impact on the Earth system have been the subject of vigorous debates across diverse disciplines, often based on disparate data. Age estimates for LUCA are usually based on the fossil record, varying with every reinterpretation. The nature of LUCA’s metabolism has proven equally contentious, with some attributing all core metabolisms to LUCA, while others reconstruct a simpler life form dependent on geochemistry. Here we show, using a set of pre-LUCA duplications under a new cross-bracing approach implemented in PAML, calibrated with microbial fossils and isotope records of metabolisms, that LUCA existed ~4.2 Ga. We use 700 prokaryotic genomes to infer a 2.59Mb+ genome encoding at least 2500 proteins, comparable to modern prokaryotes. Our results suggest LUCA was anaerobic, acetogenic and possessed an early immune system. While LUCA is sometimes perceived as living in isolation, we infer LUCA to have been part of an established ecology. The metabolism of LUCA would have provided a niche for other community members, while hydrogen recycling by atmospheric photochemistry could have supported a modestly productive early ecosystem.