January 1, 2019.
Bacterial spores embedded in a polymer matrix may be up to 10 times more resilient than spores found on the surface of a material. The resiliency of these spores could result in lower than expected microbial reduction using current standards. The goals of planetary protection are to measure, control, and reduce spacecraft microbial contamination in the attempt to minimize the chances of contaminating other worlds with Earth lifeforms or vice versa. The primary method used to microbially reduce spacecraft materials is heat microbial reduction, or HMR. In order to determine the minimum effective times and temperatures to inactivate particularly resistant bacteria, D values obtained from indicator organism survivor plots are calculated. These D values represent the time required to reduce the microbial population by 90%. Bacillus atrophaeus, a highly resistant spore forming bacterium, was embedded in 3M 2216 Scotch weld epoxy, a spacecraft material. In our experiments, samples of epoxy embedded with bacterial spores were heated at chosen temperatures for specified times, cryogenically ground, diluted, pour plated, and survivors counted. Preliminary results gave D values of 12.6 hours at 125¬∞C and 0.516 hours at 150¬∞C. Given these results, further study is necessary to confirm these higher D values than the current NASA spec.
NASA Jet Propulsion Laboratory (JPL)
The 2018 STEM Teacher and Researcher Program and this project have been made possible through support from Chevron (www.chevron.com), the National Marine Sanctuary Foundation (www.marinesanctuary.org), the National Science Foundation through the Robert Noyce Program under Grant #1836335 and 1340110, the California State University Office of the Chancellor, and California Polytechnic State University in partnership with NASA Jet Propulsion Laboratory. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the funders.