Thermal death of Bacillus subtilis var. niger spores on selected lander capsule surfaces.
Dry-heat sterilization of planetary lander capsules requires a knowledge of the thermal resistivity of microorganisms in the environment to which they will be subjected during sterilization of the space hardware. The dry-heat resistance of Bacillus subtilis var. niger spores on various lander capsule materials was determined at 125 C. Eight surface materials were evaluated, including a reference material, stainless steel. Survivor curves were computed, and decimal reduction times (D values) were obtained by a linear regression analysis. In four tests on stainless steel, the average value of D at 125 C was 17.07 min. The D values for the other seven materials tested ranged from 18.64 min on magnesium surfaces to 20.83 min on conversion-coated magnesium. Of the materials evaluated, the results indicate that there is only a significant difference in the thermal resistance of B. subtilis var. niger spores on conversion-coated magnesium and conversion-coated aluminum from that on the reference material, stainless steel. The differences in D values for all the test surfaces may be the result of variations in test procedures rather than the effect of the surfaces on the thermal resistivity of the spores.
D000497:Alloys; D000535:Aluminum; D001412:Bacillus subtilis; D018504:Ecological Systems, Closed; D006046:Gold; D006358:Hot Temperature; D008274:Magnesium; D013026:Space Flight; D013170:Spores; D013242:Sterilization; D014025:Titanium
D000497:Alloys; D006046:Gold; D000535:Aluminum; D014025:Titanium; D008274:Magnesium