Metabolism and Biodegradation of Spacecraft Cleaning Reagents by Strains of Spacecraft-AssociatedAcinetobacter

Abstract

Spacecraft assembly facilities are oligotrophic and low-humidity environments, which are routinely cleaned using alcohol wipes for benchtops and spacecraft materials, and alkaline detergents for floors. Despite these cleaning protocols, spacecraft assembly facilities possess a persistent, diverse, dynamic, and low abundant core microbiome, where the Acinetobacter are among the dominant members of the community. In this report, we show that several spacecraft-associated Acinetobacter metabolize or biodegrade the spacecraft cleaning reagents of ethanol (ethyl alcohol), 2-propanol (isopropyl alcohol), and Kleenol 30 (floor detergent) under ultraminimal conditions. Using cultivation and stable isotope labeling studies, we show that ethanol is a sole carbon source when cultivating in 0.2 × M9 minimal medium containing 26 μM Fe(NH4)2(SO4)2. Although cultures expectedly did not grow solely on 2-propanol, cultivations on mixtures of ethanol and 2-propanol exhibited enhanced plate counts at mole ratios of ≤0.50. In support, enzymology experiments on cellular extracts were consistent with oxidation of ethanol and 2-propanol by a membrane-bound alcohol dehydrogenase. In the presence of Kleenol 30, untargeted metabolite profiling on ultraminimal cultures of Acinetobacter radioresistens 50v1 indicated (1) biodegradation of Kleenol 30 into products including ethylene glycols, (2) the potential metabolism of decanoate (formed during incubation of Kleenol 30 in 0.2 × M9), and (3) decreases in the abundances of several hydroxy- and ketoacids in the extracellular metabolome. In ultraminimal medium (when using ethanol as a sole carbon source), A. radioresistens 50v1 also exhibits a remarkable survival against hydrogen peroxide (∼1.5-log loss, ∼108 colony forming units (cfu)/mL, 10 mM H2O2), indicating a considerable tolerance toward oxidative stress under nutrient-restricted conditions. Together, these results suggest that the spacecraft cleaning reagents may (1) serve as nutrient sources under oligotrophic conditions and (2) sustain extremotolerances against the oxidative stresses associated with low-humidity environments. In perspective, this study provides a plausible biochemical rationale to the observed microbial ecology dynamics of spacecraft-associated environments.

Microbiome dynamics during the HI-SEAS IV mission, and implications for future crewed missions beyond Earth

“…Although described as a skinassociated microbe [98], Acinetobacter established itself much better in various locations of the main room and bedroom. As this bacterium is also frequently detected on surfaces of public and private buildings, as well as hospitals or cleanrooms [99][100][101][102] it is tempting to speculate whether Acinetobacter could be perceived as an indicator species for con ned built environments and to a lesser extent only as a skin-associated bacterium.…”

Microbiome dynamics during the HI-SEAS IV mission, and implications for future crewed missions beyond Earth

“…Although described as a skin-associated microbe [98], Acinetobacter established itself much better in various locations of the main room and bedroom. As this bacterium is also frequently detected on surfaces of public and private buildings, as well as hospitals or cleanrooms [99][100][101][102] it is tempting to speculate whether Acinetobacter could be perceived as an indicator species for confined built environments and to a lesser extent only as a skin-associated bacterium.…”

Assembly of Bacterial Genome Sequences from Metagenomes of Spacecraft Assembly Cleanrooms

“…Members of Rhizobiaceae and Acinetobacter were previously detected in the KSC-PHSF, as well as other cleanroom environments ( 1 , 5 , 14 – 20 ). Further analysis of these MAGs will provide insight into the strategies underpinning survival in cleanroom environments and inform future sterilization strategies.…”