Prebiotic Chemical Evolution Guided by an Extraterrestrial Record
Prebiotic chemistry leading to the origin of life on early Earth may have occurred in a wide variety of environments. Unfortunately, this chemistry and its record of organic compounds from the earliest periods of Earth’s history has been completely erased by plate tectonics and overwritten by life. The study of extraterrestrial materials, particularly carbonaceous chondrite meteorites, provides a unique insight into the chemistry and processes that occurred during the formation and early evolution of the Solar System, and can inform on the prebiotic organic record available to the ancient Earth.
The Callahan Lab focuses on two areas of research: (1) investigating cyanide abundance and speciation in extraterrestrial materials and in plausibly prebiotic reactions and (2) using these ancient clues to guide laboratory experiments to understand the origin of the catalytic active site of [NiFe] hydrogenase.
1. Cosmochemistry: Cyanide Abundance and Speciation in Extraterrestrial Materials
Cyanide may arguably be the most important compound for the origin of life having been implicated in the synthesis of numerous biologically relevant compounds. A plausible source of cyanide may have come from asteroids during the Late Heavy Bombardment, which supplemented geochemical cyanide production on early Earth. However, little is known about the abundance of cyanide present in meteorites, which are fragments of asteroids (Smith et al., 2019; Reichow et al., 2023). There is even less knowledge regarding the species of cyanide, which is critical towards understanding how a volatile and reactive molecule is still detectable in meteorites (Smith et al., 2019; Reichow et al., 2023).
Current projects include: [1] measuring acid-releasable cyanide abundance in carbonaceous chondrites and [2] determining cyanide speciation in carbonaceous chondrites, particularly the distribution and abundance of simple metal-cyanide solids and iron cyanocarbonyl complexes.
Additionally, we are actively investigating the relationship between extraterrestrial soluble organic compounds and aqueous alteration (that took place in meteorite parent bodies) using state of the art ultrahigh resolution mass spectrometry and a “meteor-omics” data analysis approach.
Rachel Reichow analyzing samples with the ultrahigh resolution mass spectrometer in the Callahan Lab.
2. Prebiotic Chemistry: Exploring the Origin(s) of Hydrogenase Active Sites
Recently, the Callahan Lab discovered that cyanide (CN), along with carbon monoxide (CO), were bound with iron to form stable compounds in meteorites (Smith et al., Nature Communications, 2019). These extraterrestrial iron cyanocarbonyl complexes [Fe(CN)x(CO)y] resemble the organometallic active sites of hydrogenases, which are ancient enzymes (dating back to the Last Universal Common Ancestor, LUCA) that provide energy to bacteria and archaea by breaking down hydrogen gas (H2). Consequently, we hypothesize that iron cyanocarbonyl complexes may have been precursors to hydrogenase active sites on early Earth. The Callahan Lab is currently testing this hypothesis. This research also inspired new efforts in the Brown Lab to synthesize structural models of these active sites (enzyme mimics) via classical organometallic approaches, which we are also collaborating on.
Current projects include: [1] investigating the synthesis of iron cyanocarbonyl complexes under simulated early Earth conditions and [2] exploring how iron cyanocarbonyl complexes could have transformed to primitive [NiFe]-hydrogenase active sites on early Earth.
Past Research Projects
Extraterrestrial Nucleobases and Primitive Genetic Polymers
Meteorites provide a record of the chemical processes that occurred in the Solar System before life began on Earth. The soluble organic matter in carbonaceous chondrite meteorites is known to be incredibly complex, which includes important compounds likely necessary for the origin of life. We have studied nucleobases in meteorites for over a decade. Nucleobases serve as the structural basis of information storage in RNA and DNA and are essential for life as we know it. We have conducted targeted analyses of nucleobases in different groups of carbonaceous chondrite meteorites, discovered new nucleobase analogs in meteorites, and linked these meteoritic compounds to cyanide chemistry. Our research strongly suggested that nucleobases found in meteorites are extraterrestrial in origin ending a debate that was over 50 years old (Callahan et al., PNAS, 2011). Furthermore, we have investigated how these compounds may have contributed to the formation of primitive genetic polymers on early Earth (Smith et al., OLEB, 2016; Rodriguez et al., Scientific Reports, 2019).
Dayton Callahan sticking his head into Goose Lake Meteorite at Smithsonian National Museum of Natural History.
Biomolecular Archaeology: Tracing Back to the Earliest Wine
Biomolecular archaeology, the scientific analysis of ancient organic remains, has become invaluable towards understanding our human past and cultural evolution. In collaboration with Dr. Patrick McGovern (University of Pennsylvania Museum of Archaeology and Anthropology), we analyzed Etruscan amphorae and a limestone press (ca. 425-400 BCE) from the ancient coastal port site of Lattara in southern France (see map on right). We developed the critical analytical methods that unambiguously identified tartaric acid and malic acid, chemical indicators of grape/wine, in these samples. Direct chemical analysis along with archaeobotanical evidence and anthropological context provided the earliest proof for grape wine and viniculture from France, which is crucial to the later history of wine in Europe and the rest of the world (McGovern et al., PNAS, 2013). We also analyzed numerous early Neolithic pottery sherds (and associated soil samples) excavated from the sites Gadachrili Gora and Shulaveris Gora in Georgia. Our chemical analysis, along with archaeobotanical evidence and climatic and environmental reconstruction, points to grape wine and viniculture from the Near East as early as ca. 6000 BCE (McGovern et al., PNAS, 2017). After over a decade of research, we have decided to end our studies in biomolecular archaeology.
Food, Energy, and Water Systems
Alison Good working with extracts of algal biomass. Photo credit: Allison Corona, BSU
Algae has the potential to be a sustainable source of biomass and oils for food, animal feed, fuel, and bioproducts in addition to their utilization of nutrients from a variety of wastewaters, which can reduce costs. There is a need for high-throughput and rapid screening methods for lipids and other organics to evaluate the optimal treatment conditions for the production of oil-rich (high lipid content) algae. This need is further supported by the fact that only a fraction of algae species has been explored for the production of biofuels due to their large diversity. We collaborated with Prof. Kevin Feris (Department of Biological Sciences, Boise State University) and his research group to investigate fatty acid composition of algae polycultures grown in dairy wastewater and how polyculture selection could influence lipid and fatty acid production (Thomas et al., Algal Research, 2019). The good news was that we worked with algal biomass instead of the dairy manure.
Research Collaborators (click on photo to link to their website)
Dr. Adam Colson
Dr. Patrick McGovern, U. Penn. Museum of Archaeology and Anthropology
Dr. Henderson (Jim) Cleaves, Earth-Life Science Institute, Tokyo Institute of Technology
Prof. Eric Brown, Department of Chemistry and Biochemistry, Boise State University
Prof. Christopher House, Department of Geosciences, Penn State University
Dr. Aaron Burton, ARES Division, NASA Johnson Space Center
Some previous research collaborators include Conel Alexander (Carnegie Institute of Washington), Ricardo Arévalo, Jr. (University of Maryland), Manuel Balvin (NASA Goddard Space Flight Center), Kevis Feris (Boise State University), Perry Gerakines (NASA Goddard Space Flight Center), Stephanie Getty (NASA Goddard Space Flight Center), Yassin Jeilani (Spelman College), and Gerrick Lindberg (Northern Arizona University).
Funding provided by:
