Figure 2From: Measurement of microbial activity in soil by colorimetric observation of in situ dye reduction: an approach to detection of extraterrestrial lifeColor change resulting from the microbial reduction in soil of the respiratory dye XTT Bottle on the far left is a control of the oxidized dye in sterile water. The middle bottle shows lack of dye reduction by a sandy soil that was autoclaved. The bottle on the far right shows dye reduction (increase in orange color measurable at 465 nm) from a biologically active (contains living bacteria) sandy soil.Back to article page