Response of the spacecraft isolate Acinetobacter radioresistens 50V1 to copper-containing antimicrobial materials and their relevance to Planetary Protection

Abstract

During life-detection mission on Mars, Planetary Protection policies ensure that forward and backward contaminations are avoided. However, some extremotolerant strains like Acinetobacter radioresistens 50V1 can proliferate despite the strict cleaning protocols aboard a spacecraft and thus interfere with space exploration. To avoid contaminations improved and novel disinfection techniques are needed, for example utilizing materials with intrinsic antimicrobial properties. In this thesis the response of A. radioresistens 50V1 to desiccation, vacuum, copper-containing surfaces and solutions was examined and compared to the type strain A. radioresistens DSMZ 6976. Desiccation on steel for a week induced significant decrease in the survival fractions of both strains, whereas in vacuum both 50V1 and DSMZ 6976 exhibited higher survivability than after desiccation alone. Under both conditions 50V1 demonstrated higher survival fractions than DSMZ 6976. When the two Acinetobacter strains were deposited on plastic copper-containing materials with 0.5% or 6.64% CuSO4, neither of the bacteria was inactivated. When exposed to copper and copper alloys containing more than 60% of copper, DSMZ 6976 was completely neutralized in less than two hours. 50V1 demonstrated higher survivability than the type strain for all of the metallic materials. Nevertheless, significant reduction in the survivability of the spacecraft contaminant was determined for all of the tested alloys. Examining the growth of 50V1 in copper-containing media revealed that 1 mM of CuSO4 or CuCl2 affects only the growth rate of the NASA isolate. In contrast, DSMZ 6976 could not proliferate under these conditions and demonstrated decreased viable count over time. Based on these observations, it can be concluded that 50V1 is more resistant than DSMZ 6976 to all of the tested stress factors. However, both strains have the potential to be persistent spacecraft contaminants due to their tolerance to desiccation and vacuum. However, utilizing coppercontaining materials and solutions with sufficiently high copper concentrations can diminish such contaminations in alignment with Planetary Protection goals.