Open Access Highly Accessed Methodology article

Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial life

Ronald L Crawford1*, Andrzej Paszczynski1, Qingyong Lang2, Daniel P Erwin1, Lisa Allenbach1, Giancarlo Corti4, Tony J Anderson4, I Francis Cheng2, Chien Wai2, Bruce Barnes3, Richard Wells3, Touraj Assefi5 and Mohammad Mojarradi6

Author Affiliations

1 Environmental Biotechnology Institute; University of Idaho, Moscow ID 83844

2 Departments of Chemistry, University of Idaho, Moscow ID 83844

3 Electrical Engineering, University of Idaho, Moscow ID 83844

4 Mechanical Engineering; University of Idaho, Moscow ID 83844

5 Microelectronics Research and Communication Institute, University of Idaho, Moscow ID 83844

6 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA

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BMC Microbiology 2002, 2:22  doi:10.1186/1471-2180-2-22

Published: 31 July 2002



Detecting microbial life in extraterrestrial locations is a goal of space exploration because of ecological and health concerns about possible contamination of other planets with earthly organisms, and vice versa. Previously we suggested a method for life detection based on the fact that living entities require a continual input of energy accessed through coupled oxidations and reductions (an electron transport chain). We demonstrated using earthly soils that the identification of extracted components of electron transport chains is useful for remote detection of a chemical signature of life. The instrument package developed used supercritical carbon dioxide for soil extraction, followed by chromatography or electrophoresis to separate extracted compounds, with final detection by voltammetry and tandem mass-spectrometry.


Here we used Earth-derived soils to develop a related life detection system based on direct observation of a biological redox signature. We measured the ability of soil microbial communities to reduce artificial electron acceptors. Living organisms in pure culture and those naturally found in soil were shown to reduce 2,3-dichlorophenol indophenol (DCIP) and the tetrazolium dye 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). Uninoculated or sterilized controls did not reduce the dyes. A soil from Antarctica that was determined by chemical signature and DNA analysis to be sterile also did not reduce the dyes.


Observation of dye reduction, supplemented with extraction and identification of only a few specific signature redox-active biochemicals such as porphyrins or quinones, provides a simplified means to detect a signature of life in the soils of other planets or their moons.