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Project Progress

We have continued our investigations into organic biogeochemistry in extreme environments on Earth and the implications for extraterrestrial organic biomarker searches. We are preparing to submit a manuscript describing our analysis of amino acid concentration vs. depth profiles in microbially colonized Antarctic sandstone rocks. We have found an interesting phenomenon in which one or more as yet unidentified molecules containing D-alanine and D-glutamic acid appear to pool at significant depths (up to 10 cm or more) inside the rock, while a second fraction containing D-aspartic acid and D-leucine is concentrated near the surface of the rock, at the level of highest biomass occurrence. These two contrasting profiles may be due to differential breakdown and aqueous transport of peptidoglycans or other biomacromolecules produced by the cryptoendolithic community. This discovery has important implications for the design of spacecraft amino acid analysis instrumentation that might be used to search for similar biological communities on Mars.

We are also extending our database of amino acid and lipid biomarker profiles from low-water-activity environments to include samples of possible Mojave Desert endoliths. These samples include rocks coated with desert varnish, a layer of metal oxides and clays that has been speculated to have a biologically mediated formation mechanism. A USC Geobiology graduate student, Rachel Schelble, is searching for bacterial fatty acid biomarkers in the varnish layers of these samples at JPL under a NASA Planetary Biology Internship.

We have also been investigating possible prebiotic organic chemistry on Titan through the use of laboratory-produced haze analog materials known as tholins. In collaboration with George Cody of the Carnegie Institution NAI team, we have obtained high-resolution ¹H, ¹³C and ¹⁵N nuclear magnetic resonance (NMR) spectra of one form of Titan tholin. We are currently in the process of assembling those data into a model chemical structure. This structure will give us greater insight into the chemistry that may occur when atmospheric organic haze particles interact with water, rock, or hydrocarbon phases on the surface of Titan.