Background Bacillus spores are notoriously resistant to unfavorable conditions such as UV radiation, γ-radiation, H2O2, desiccation, chemical disinfection, or starvation. Bacillus pumilus SAFR-032 survives standard decontamination procedures of the Jet Propulsion Lab spacecraft assembly facility, and both spores and vegetative cells of this strain exhibit elevated resistance to UV radiation and H2O2 compared to other Bacillus species.Principal FindingsThe genome of B. pumilus SAFR-032 was sequenced and annotated. Lists of genes relevant to DNA repair and the oxidative stress response were generated and compared to B. subtilis and B. licheniformis. Differences in conservation of genes, gene order, and protein sequences are highlighted because they potentially explain the extreme resistance phenotype of B. pumilus. The B. pumilus genome includes genes not found in B. subtilis or B. licheniformis and conserved genes with sequence divergence, but paradoxically lacks several genes that function in UV or H2O2 resistance in other Bacillus species.SignificanceThis study identifies several candidate genes for further research into UV and H2O2 resistance. These findings will help explain the resistance of B. pumilus and are applicable to understanding sterilization survival strategies of microbes.

A life-detection system based on the expectation that any viable organism will utilize stereoisomers of a given compound asymmetrically is examined. Aqueous extracts of common soil, Mars regolith simulant JSC Mars-1, and suspensions of E. coli and S. cerevisiae were incubated with stereoisomer pairs. The enantiomeric pairs were either D- and L-glucose or a pair of chiral tetrasaccharides. Following an incubation period of 10 days, stereoisomeric selectivity is detectable with the glucose pair by mass spectrometry in extracts made from soil at 0.5 g/ml, in extracts made from JSC Mars-1 at 2.5 g/ml, and in cell suspensions down to 1.0 x 10(7) cells/ml. For the tetrasaccharide pair, stereoisomeric selectivity was detected in extracts made from 0.5 g/ml or more of common soil but not in JSC Mars-1 simulant. The effective sensitivity in extracts was 2.5 x 10(7) cells/ml or better for the glucose pair and 5.0 x 10(8) cells/ml or better for the tetrasaccharide pair. The sensitivity of the glucose pair was such that it could detect life in samples that would be found to be devoid of organic matter by the GCMS system carried by the Viking landers. The results demonstrate the utility of the approach in the search for biological activity on Mars. However, sensitivity is a function of the enantiomer pair used, and this might also be different for hypothetical martian organisms. Therefore, it will be necessary to characterize additional stereoisomeric pairs and, ultimately, to include several in a single test environment.