Evaluation of Various Cleaning Methods to Remove Bacillus Spores from Spacecraft Hardware Materials

Abstract

A detailed study was made of the biological cleaning effectiveness, defined in terms of the ability to remove bacterial spores, of a number of methods used to clean hardware surfaces. Aluminum (Al 6061) and titanium (Ti 6Al-4V) were chosen for the study as they were deemed the two materials most likely to be used in spacecraft extraterrestrial sampler construction. Metal coupons (1 cm x 2.5 cm) were precleaned and inoculated with 5.8 x 10(3) cultivable Bacillus subtilis spores, which are commonly found on spacecraft surfaces and in the assembly environments. The inoculated coupons were subsequently cleaned using: (1) 70% isopropyl alcohol wipe; (2) water wipe; (3) multiple-solvent flight-hardware cleaning procedures used at the Jet Propulsion Laboratory (JPL); (4) Johnson Space Center-developed ultrapure water rinse; and (5) a commercial, semi-aqueous, multiple-solvent (SAMS) cleaning process. The biological cleaning effectiveness was measured by agar plate assay, sterility test (growing in liquid media), and epifluorescent microscopy. None of the cleaning protocols tested completely removed viable spores from the surface of the aluminum. In contrast, titanium was capable of being cleaned to sterility by two methods, the JPL standard and the commercial SAMS cleaning process. Further investigation showed that the passivation step employed in the JPL standard method is an effective surface sterilant on both metals but not compatible with aluminum. It is recommended that titanium (Ti 6Al-4V) be considered superior to aluminum (Al 6061) for use in spacecraft sampling hardware, both for its potential to be cleaned to sterilization and for its ability to withstand the most effective cleaning protocols.

Multifactorial Resistance ofBacillus subtilisSpores to High-Energy Proton Radiation: Role of Spore Structural Components and the Homologous Recombination and Non-Homologous End Joining DNA Repair Pathways

“…In the context of planetary protection, bacterial spores have been identified as major spacecraft contaminants of concern in the prevention of forward contamination of astrobiologically interesting bodies such as Mars (Venkateswaran et al, 2004;Bruckner et al, 2008;Nicholson et al, 2009). The data reported in this communication also suggest that bacterial spores contaminating UV-shielded or interior portions of spacecraft would be exposed to insufficient proton radiation for their complete inactivation during a typical Earth-to-Mars voyage of 6-8 months' duration.…”

Effect of Shadowing on Survival of Bacteria under Conditions Simulating the Martian Atmosphere and UV Radiation

“…In this study, vegetative cells (not spores) that had been desiccated on aluminum exhibited inconsistent survival following 24 h of exposure to a simulated Martian diurnal atmosphere (see Table S2 in the supplemental material). This could have been a consequence of the uneven surface geometry of the aluminum (47), which may have resulted in small areas where there was UV shielding. Such a reduction in Martian UV flux was modeled to facilitate the persistence of hardy terrestrial microorganisms like B. pumilis SAFR-032 for several tens of Martian years (29).…”

Evaluation of Procedures for the Collection, Processing, and Analysis of Biomolecules from Low-Biomass Surfaces

“…thick) coupons (25 cm 2 ) and sheets (2,500 cm 2 ) were precleaned with cleanroom-grade polyester wipes (Coventry 6209 c-prime; Tech Spray, L.P., Amarillo, TX). Coupons and sheets were subjected to ultrasonic cleaning with alkaline detergent soap (815 GD; Brulin, Indianapolis, IN) at 160°F, followed by a deionized-water rinse, drying, and a final rinse with 97% ethyl alcohol (40). Subsequently, coupons and sheets were rinsed with deionized water and dried with clean, dry nitrogen.…”