AbstractsBiology & Animal Science

Spacecraft assembly facilities are oligotrophic environments that exert selective pressures towards desiccation and radiation tolerance, thereby potentially increasing the probability for contamination of explored planetary bodies. In this thesis, the oxidative extremotolerance of Acinetobacter radioresistens 50v1, a bacterium isolated from the Mars Odyssey spacecraft, was measured under nutrient poor and low salt conditions, which served as an analog to the conditions employed during spacecraft assembly. Under minimal conditions (0.2 x M9), with ethanol serving as a sole carbon source, A. rad. 50v1 exhibited a 0.5 to 1-log reduction in survival (from ~108 cells) upon exposure to 10 mM aqueous hydrogen peroxide (H2O2), depending on ethanol concentration, and no measurable growth in 100 mM H2O2. In comparison, no loss in survival was observed at either H2O2 concentration under nutrient rich conditions (Lysogeny broth). Under minimal conditions (10 mM H2O2), the impact of the sole transition metal was quite profound, with Mn2+ yielding an ~10-fold increase in survival when compared to Fe2+. Interestingly, at 20 mM H2O2, no loss in survival was measured with Mn2+, whereas no measurable growth was observed with Fe2+ and Mn2+. The role of catalase in the survivability was also addressed by measuring the specific activity from fractionated cells. In summary, these results supported the presence of a membrane bound catalase and culture-dependent expression of Fe and Mn-catalases. Together, these studies show that A. radioresistens 50v1 displays a moderate oxidative extremotolerance under oligotrophic conditions, which suggests a potential for tolerance towards the cleaning conditions used during spacecraft assembly, and the concomitant increase in the potential for forward contamination by the Acinetobacter. Advisors/Committee Members: Mogul, Rakesh (advisor), Alex, Lisa (committee member).