Thermal Death of Bacillus subtilis var. niger Spores on Selected Lander Capsule Surfaces

Abstract

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 conversioncoated 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.

Thermal resistance of Bacillus subtilis var. niger in a closed system

“…Representative of recent work are reports by Angelotti et al (2), Paik et al (7), Wardle et al (12), and Simko et al (11), which describe the thermal destruction of B. subtilis var. niger.…”

Dry-Heat Resistance of Bacterial Spores Recovered from Mariner-Mars 1969 Spacecraft

“…It is imperative that an understanding of the dry-heat resistance of microorganisms on spacecraft that require sterilization, i.e., landers for an extraterrestrial life-detection mission, be acquired (6). An important step toward obtaining this necessary knowledge for the determination of a sterilization cycle for such a spacecraft was made by the prelaunch recovery of spore isolates from the Mariner-Mars 1969 flybys.…”