title: Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial life.
abstract: BACKGROUND
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Environmental Biotechnology Institute, University of Idaho, Moscow 83844, USA. crawford@uidaho.edu
authors.forename: Ronald
authors.initials: R
authors.lastname: Crawford
authors.forename: Andrzej
authors.initials: A
authors.lastname: Paszczynski
authors.forename: Qingyong
authors.initials: Q
authors.lastname: Lang
authors.forename: Daniel
authors.initials: D
authors.lastname: Erwin
authors.forename: Lisa
authors.initials: L
authors.lastname: Allenbach
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Corti
authors.forename: Tony
authors.initials: T
authors.lastname: Anderson
authors.forename: I
authors.initials: I
authors.lastname: Cheng
authors.forename: Chien
authors.initials: C
authors.lastname: Wai
authors.forename: Bruce
authors.initials: B
authors.lastname: Barnes
authors.forename: Richard
authors.initials: R
authors.lastname: Wells
authors.forename: Touraj
authors.initials: T
authors.lastname: Assefi
authors.forename: Mohammad
authors.initials: M
authors.lastname: Mojarradi
mesh_terms: D001419:Bacteria / Q000302:isolation & purification / Q000378:metabolism*; D003124:Colorimetry; D004396:Coloring Agents / Q000378:metabolism*; D005118:Extraterrestrial Environment; D010084:Oxidation-Reduction; D011166:Porphyrins / Q000032:analysis; D011809:Quinones / Q000032:analysis; D012988:Soil Microbiology
chemical_list: D004396:Coloring Agents; D011166:Porphyrins; D011809:Quinones