Survival of Bacillus subtilis endospores after exposure of Mars surrogate soil to the sterilizing radiation of UV. Each data point represents the mean of three replicate experiments. Error bars represent +/- one standard deviation of the three replicates. CFU = colony-forming units. The X-axis shows the depth range (mm) of the sample taken for viable counts after 96 hours of exposure to UV light.
Crawford et al. BMC Microbiology 2003 3:4 doi:10.1186/1471-2180-3-4