Amanda Garcia

Postdoctoral Research Associate, Molecular and Cellular Biology

I study resurrected ancient enzymes involved in biogeochemical cycles of early Earth, and connect their properties to preserved signatures in the geologic record.

The history of life on Earth is written both in the geologic record and the genomes of modern organisms. My research aims to connect these two sources of information by using experimentally investigated properties of “resurrected” ancient enzymes to interpret preserved biosignatures in the geologic record. These insights can help us understand how life and the environment have coevolved over billions of years on our planet, and, potentially, on other worlds as well.

Several ancient and important enzymes are the gatekeepers between metabolic systems and the surrounding geochemical environment. The evolution of their functional properties has modulated the global habitability of the Earth system over billions of years. Their activities have also left geochemical “fingerprints”, otherwise known as biosignatures, which can give us clues towards their ancient function as well as date their presence in Earth’s history. However, accurate interpretations of these biosignatures cannot be made using properties of modern enzymes, which may not function in the same way as their ancestral counterparts once did. To resolve this problem, I use phylogenetic tools to computationally reconstruct the sequences of these ancient enzymes, incorporate their encoding genes in modern microbial genomes, and characterize their functions within a biogeochemical context.

I am currently working with the nitrogenase enzyme family, which is the only enzyme capable of “fixing” atmospheric nitrogen such that it is biologically usable. The trajectory of more than three billion years of nitrogenase evolution has been affected by the progressive oxygenation of the Earth’s atmosphere, and that trajectory can be discerned through the nitrogen isotope record measured in sedimentary rocks. By resurrecting ancient nitrogenases in bacteria and characterizing their isotope fractionation capabilities, we can better understand this record as well as the early evolution of nitrogen fixation.

These approaches offer exciting new ways to interrogate historical records of life, setting a standard for the interpretation of similar signatures we might find in our exploration of the universe.