Matthew Koehler, Ph.D.
Laboratory for Research in Complex Systems
University of Washington (Ph.D., Earth & Space Sciences with Roger Buick)
Visiting Scientist, NASA/JPL (Ken Williford's Lab)
Early Earth: Evolution of Life and Environment
Life’s evolutionary history on Earth is recorded in two natural repositories – modern biology and the geologic record. I explore the latter. Most recently, we have been thinking about the following question: Could one recognize the transition from an abiotic and a biotic world in Earth’s poorly-preserved geologic record? Signs of life before 3.5 billion years ago are notoriously ambiguous due to poor preservation, such that it is difficult to determine when life first evolved on our planet. These disputed “biosignatures” are primarily in the form of micron-sized organic carbon domains trapped in Earth’s oldest metasedimentary rocks. Using a suite of modern micro-analytical techniques, we are investigating whether carbon trapped in ~3.8 billion year old metasediments from southwest Greenland are in fact remains of life that lived ~3.8 billion years ago. This requires proving that the carbon was created by living organisms, and that it was deposited at the same time as the sediments; a tall order considering these rocks have experienced billions of years of tectonic deformation, metamorphism, and hydrothermal alteration.
Figure 1. Looking closely, micron-sized bits of organic carbon are observed trapped in some of Earth’s oldest sedimentary rocks – formed ~3.8 billion years ago (for perspective, a micron is to a meter, what a meter is to the distance between New York City and Minneapolis). We are attempting to investigate if this and other specimens are some of the oldest evidence of life on Earth.
As a result of this work, collaborators and I will define best-practices for holistically assessing microbiosignatures in-situ, using current technology. These methods will be a guide for future studies investigating organic carbon in Earth’s most ancient rocks, and for the analysis of future Mars return samples. Furthermore, our exhaustive assessment may edge out some of the ambiguity associated with the biosignatures at this locality, or help quantify limitations in our interpretations.
Isotopic Substitutions in Cellular Machinery
Recently, we have been thinking a lot about how the thermal properties of a material can change depending on its isotopic composition. For example, diamonds are solely composed of carbon. A diamond with relatively more of the isotope 13C compared to the isotope 12C will have a different heat capacity than a diamond with relatively less 13C. Could this same phenomenon occur in biological materials with any serious consequences? One of my emerging research interests is how isotopic substitutions in cellular machinery can affect cell function. As a pilot study into this topic, I am investigating how changing hydrogen, carbon, and nitrogen isotopes within bacterial spores might affect spore heat tolerance.
This project is in collaboration with NASA JPL’s Planetary Protection group. Understanding the underlying mechanisms of bacterial spore heat tolerance is important to them, because heat-resistant bacterial spores can survive their spacecraft sterilization protocol. Is it possible to lower an organism’s heat tolerance with isotopic bioengineering? What other cell qualities and function might be modulated with well-placed isotopic substitutions? These are some of the questions I am excited to explore.
Koehler MC, Buick R, Kipp MA, Stüeken EE, Zaloumis J. Transient surface ocean oxygenation recorded in the ∼2.66-Ga Jeerinah Formation, Australia. Proc Natl Acad Sci U S A. 2018 Jul 24;115(30):7711-7716. doi: 10.1073/pnas.1720820115. Epub 2018 Jul 9. Erratum in: Proc Natl Acad Sci U S A. 2018 Aug 28;115(35):E8323. PubMed PMID: 29987010; PubMed Central PMCID: PMC6065012.
Misra A, Krissansen-Totton J, Koehler MC, Sholes S. Transient Sulfate Aerosols as a Signature of Exoplanet Volcanism. Astrobiology. 2015 Jun;15(6):462-77. doi: 10.1089/ast.2014.1204. Epub 2015 Jun 8. PubMed PMID: 26053611.
Stüeken EE, Buick R, Guy BM, Koehler MC. Isotopic evidence for biological nitrogen fixation by molybdenum-nitrogenase from 3.2 Gyr. Nature. 2015 Apr 30;520(7549):666-9. doi: 10.1038/nature14180. Epub 2015 Feb 16. PubMed PMID: 25686600.
Title: Testing the role of isotopic composition and heterogeneity in the heat tolerance of bacterial spores
Type: R&TD Innovative Spontaneous Concept Proposal