The ultimate goal of planetary protection research is to develop superior strategies for inactivating resistance-bearing micro-organisms like Rummelibacillus stabekisii. By first identifying the particular physiologic pathway and/or structural component of the cell/spore that affords it such elevated tolerance, eradication regimes can then be designed to target these resistance-conferring moieties without jeopardizing the structural integrity of spacecraft hardware. Furthermore, hospitals and government agencies frequently use biological indicators to ensure the efficacy of a wide range of sterilization processes. The spores of Rummelibacillus stabekisii, which are far more resistant to many of such perturbations, could likely serve as a more significant biological indicator for potential survival than those being used currently.
Numerous surveys of the contaminant microbial diversity housed within spacecraft assembly facilities over the past six years have resulted in the recurrent isolation of spore-forming bacteria belonging to the Bacillus genus. As Bacillus species are capable of existing as metabolically inactive, extremely hardy spores, many lineages exhibit remarkable resilience to varying modes of bioreduction/sterilization aimed at their eradication (UV and gamma radiation, oxidizing disinfectants, etc.). The microorganism Rummelibacillus stabekisii sp. nov. was isolated from the surfaces of the cleanroom facility in which the Mars Exploration Rovers (MER) underwent assembly. This bacterium has not been previously reported, and shows no close relation to any previously described species (as is assessed via 16S rRNA gene sequence comparison). This unique isolate, and the Bacillus species most genetically similar to it, were subjected to a multitude of biochemical tests in order to thoroughly characterize its taxonomic position based on physiological and phylogenetic evidence. The results clearly show that this bacterium is significantly different from its nearest relatives.
The microbial colonization of spacecraft and cleanroom assembly facility surfaces is of major concern to NASA and others commissioning modern-day space exploration. The search for life elsewhere in the solar system will rely heavily on validated cleaning and sterility methods. It would be devastating to the integrity of a mission directed at pristine environments such as the Europa’s subsurface ocean or the Martian polar caps to be compromised as a result of terrestrial microbial contamination. To this end, planetary protection policies are in place to ensure the cleanliness and sterility of mission-critical spacecraft components in order to prevent forward or backward contamination.
Spores of Bacillus subtilis, a model spore-forming laboratory strain that demonstrates higher susceptibility to ultraviolet and gamma radiation than other wild type spore formers, have nevertheless been shown to survive up to six years under interstellar space conditions. Previously undescribed sporeforming species, such as Rummelibacillus stabekisii, may exhibit even greater resilience. It is in the best interests of NASA to thoroughly understand the physiological capabilities of each and every novel micro-organism isolated from these spacecraft-associated cleanrooms.