Abstract
Biological life-support systems could greatly increase the sustainability of crewed missions to the Moon or Mars. Understanding how bacteria react to hypobaria is critical to their optimization: if enclosed within crewed compartments, microbial modules may be exposed to the lower-than Earth atmospheric pressure considered for future space vehicles and habitats and, if deployed outside, they would best rely on a low pressure to minimize both engineering constraints and risks of leakage. Bacterial behavior at low pressures is of relevance to other fields as well, both within astrobiology (e.g., habitability and planetary protection) and outside of it (e.g., aerobiology and food preservation). Unfortunately, while microbial survival under vacuum has been largely investigated, little work has focused on metabolism at low but growth-permissive pressures. Nonetheless, recent studies brought some insights. Limits were outlined: a few bacterial species can grow just above water’s triple point, more can multiply down to around 25 mbar, and shifting pressure within 100 mbar to 1 bar seems not to largely affect growth of most species when the partial pressures of metabolizable gases are not limiting. Some mediating mechanisms have been proposed: hypobaria can affect bacteria by desiccation, via a reduced availability of specific gases, and through various other physico-chemical effects, interdependent and dependent on other environmental factors. A limited number of studies also gave insights into how bacteria cope with low pressure, and how much they can adapt to it. But, overall, much remains to be discovered on bacterial growth under hypobaric conditions.
Highlights
Data is scarce on how microorganisms cope with low pressure
If enclosed within crewed compartments, for instance to contribute to air revitalization, they may be exposed to atmospheric conditions differing from Earth’s: future space vehicles, and Moon and Mars habitats, may rely on a lower total pressure and increased O2 concentration (e.g., 0.55 bar, 32% O2; NASA, 2006) for engineering considerations, for reducing the amounts of necessary gas consumables, and to facilitate extravehicular activities while maintaining low risks of decompression sickness (e.g., NASA, 2006; Norcross et al, 2013)
Further evidence on the role of partial pressures comes from the fact that growth inhibition of E. coli K12 in LB at 50 and 25 mbar was attenuated by the addition of substrates for anaerobic metabolism (Schuerger et al, 2013), suggesting a role of decreased oxygen availability in the effect of reduced total pressure
Summary
Laboratory of Applied Space Microbiology, Center of Applied Space Technology and Microgravity (ZARM), University of Bremen, Bremen, Germany. Understanding how bacteria react to hypobaria is critical to their optimization: if enclosed within crewed compartments, microbial modules may be exposed to the lower-than-Earth atmospheric pressure considered for future space vehicles and habitats and, if deployed outside, they would best rely on a low pressure to minimize both engineering constraints and risks of leakage. Bacterial behavior at low pressures is of relevance to other fields as well, both within astrobiology (e.g., habitability and planetary protection) and outside of it (e.g., aerobiology and food preservation). While microbial survival under vacuum has been largely investigated, little work has focused on metabolism at low but growth-permissive pressures. A limited number of studies gave insights into how bacteria cope with low pressure, and how much they can adapt to it.
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