N-130. Molecular Microbial Burden and Community Analyses of Phoenix Spacecraft Assembly

S. Osman, S. Ghosh, P. Vaishampayan, K. Venkateswaran;
NASA-Jet Propulsion Lab., Pasadena, CA.

The microbial burden and diversity on and around the Phoenix spacecraft (s/c) payload during various stages of the spacecraft assembly, testing, and launching operations were examined. Samples were obtained from exposed s/c surfaces and the facilities in which the s/c is assembled. Bioburden was assessed with both the current NASA standard assay, which is limited to the enumeration of bacterial spores, and a suite of NASA-certified, cultivation independent bio-molecule-based detection assays. The biodiversity of bacteria and archaea present in these samples were determined using 16S rRNA gene analysis. To isolate extremophilic bacteria that could potentially survive conditions experienced en route to Mars and on the planet itself, a series of cultivation assays were performed to promote growth of a variety of bacteria including thermophiles, psychrophiles, halophiles, and anaerobes. Only ~10% of the total viable microbial population as measured by ATP assay was able to grow in R2A medium (mesophiles; 25°C), and among the mesophiles, only 1 to 3% were spore-forming bacteria. The significant number of alkalophiles (pH 9.0; ~15%), psychrophiles (4°C; 7 to 15%), and anaerobes (~1 to 15%) when compared to the incidence of spores (1 to 3%) is worth mentioning. The percent incidence of UVC resistant bacteria (0 to 3%) was equal to spore bioburden. A lower percentage of acidophiles (pH 9.0; <1%) and thermophiles (65°C; <1%) were also isolated, possibly due to the cleaning conditions and controlled temperatures of the assembly environment. Further characterization will determine if a significant proportion of these isolates are capable of spore formation, and to the extent that non spore-forming bacteria are associated with extremophily. Phenomena of this type are acknowledged by NASA which recognizes the need for technologies capable of determining the actual bioburden present on spacecraft-associated surfaces. The use of a surrogate for estimating overall bioburden is no longer considered sufficient to account for the organisms most resistant to spacecraft sterilization procedures and the expected environmental conditions of the mission.