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Record 1 of 4762
Amino Acid Analyses of Acid Hydrolysates in Desert Varnish
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Author and Affiliation:
Perry, Randall S.(Washington Univ., Dept. of Earth and Space Sciences, Seattle, WA United States)
Staley, James T.(Washington Univ., Dept. of Microbiology and Immunology, Seattle, WA United States)
Dworkin, Jason P.(NASA Ames Research Center, Moffett Field, CA United States)
Engel, Mike(Oklahoma Univ., School of Geology and Geophysics, Norman, OK United States)
Abstract: There has long been a debate as to whether rock varnish deposits are microbially mediated or are deposited by inorganic processes. Varnished rocks are found throughout the world primarily in arid and semi-arid regions. The varnish coats are typically up to 200 microns thick and are composed of clays and alternating layers enriched in manganese and iron oxides. The individual layers range in thickness from 1 micron to greater than 10 microns and may continue laterally for more than a 100 microns. Overlapping botryoidal structures are visible in thin section and scanning electron micrographs. The coatings also include small amounts of organic mater and detrital grains. Amino-acid hydrolysates offer a means of assessing the organic composition of rock varnish collected from the Sonoran Desert, near Phoenix, AZ. Chromatographic analyses of hydrolysates from powdered samples of rock varnish suggest that the interior of rock varnish is relatively enriched in amino acids and specifically in d-alanine and glutamic acid. Peptidoglycan (murein) is the main structural component of gram-positive bacterial cell walls. The d-enantiomer of alanine and glutamic acid are specific to peptidoglycan and are consequently an indicator for the presence of bacteria. D-alanine is also found in teichoic acid which is only found in gram-positive bacteria. Several researchers have cultured bacteria from the surface of rock varnish and most have been gram-positive, suggesting that gram-positive bacteria are intimately associated with varnish coatings and may play a role in the formation of varnish coatings.
Publication Date: Apr 01, 2001
Document ID:
(Acquired Dec 28, 2001)
Subject Category: EXOBIOLOGY
Document Type: Conference Paper
Publication Information: General Meeting of the NASA Astrobiology Insititute; 125; (SEE 20020002018)
Financial Sponsor: NASA Ames Research Center; Moffett Field, CA United States
Organization Source: NASA Ames Research Center; Moffett Field, CA United States
Description: 1p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
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