Astrobiological research in the Summons laboratory is directed toward documenting the molecular and isotopic fingerprints of extant microbes in such a way that is useful for evaluating the geochemical fossil record. We focus on organisms that are particularly important components of the biogeochemical carbon cycle, such as cyanobacteria, methanogens and methanotrophs. In collaboration with Linda Jahnke of NASA, we have been studying the lipid compositions of methane oxidizing bacteria. These organisms oxidize methane with an obligate requirement for molecular oxygen and so can be indictors of an active methane cycle as well as aerobic metabolism. They also produce a range of diagnostic fatty acids, bacteriohopane polyols and methyl sterols that can be recognized in both modern and ancient sediments. More recently we have measured the lipid compositions and carbon isotopic fractionation patterns of many strains of cultured cyanobacteria with an emphasis on branched hydrocarbons and bacteriohopane polyols. These particular types of compounds have a fossil record that extends to more than two and a half billion years ago. We found that about half of the cyanobacteria studied produce 2-methylbacteriohopane polyols which have recognizable fossil counterparts, the 2-methyl hopanes. Since very few other bacteria are capable of synthesizing these compounds, we believe they are a valuable proxy for cyanobacteria as well as an indicator of oxygenic photosynthesis in the past.

A complementary research activity focuses on the hydrocarbon compositions of ancient organic rich sediments and petroleum. The presence of particular kinds of molecular fossils present can be diagnostic for types of microbes living at the time these materials were laid down. In particular, we are studying sediments that were deposited during periods of high biological turnover such as extinction and radiation events for clues about the processes or environmental conditions that drive evolutionary change.

Facilities and equipment:
The Summons Laboratory at MIT has a range of state-of-the-art equipment for analytical and isotope mass spectrometry. A Finnigan Delta XP with Trace GC and Elemental Analyzer is configured for carbon and hydrogen isotopic analyses of individual compounds as well as analyses of organic and inorganic carbon phases. A Micromass Autospec Ultima Q is configured for high resolution GC-MS and GC-MS-MS analysis of hydrocarbons and other lipids.

Astrobiology courses:
MIT 12.009 Geobiology; MIT TBA Molecular Geochemistry

Principal NAI collaborators:
Linda Jahnke and David Des Marais: NASA Ames Research Center (ARC NAI Node); Malcolm Walter and Graham Logan: Australian Centre for Astrobiology; Kai-Uwe Hinrichs, John Hayes and Helen Sturt: WHOI (University of Rhode Island NAI Node)