Effect of spaceflight on Pseudomonas aeruginosa final cell density is modulated by nutrient and oxygen availability

Abstract

BackgroundAbundant populations of bacteria have been observed on Mir and the International Space Station. While some experiments have shown that bacteria cultured during spaceflight exhibit a range of potentially troublesome characteristics, including increases in growth, antibiotic resistance and virulence, other studies have shown minimal differences when cells were cultured during spaceflight or on Earth. Although the final cell density of bacteria grown during spaceflight has been reported for several species, we are not yet able to predict how different microorganisms will respond to the microgravity environment. In order to build our understanding of how spaceflight affects bacterial final cell densities, additional studies are needed to determine whether the observed differences are due to varied methods, experimental conditions, or organism specific responses.ResultsHere, we have explored how phosphate concentration, carbon source, oxygen availability, and motility affect the growth of Pseudomonas aeruginosa in modified artificial urine media during spaceflight. We observed that P. aeruginosa grown during spaceflight exhibited increased final cell density relative to normal gravity controls when low concentrations of phosphate in the media were combined with decreased oxygen availability. In contrast, when the availability of either phosphate or oxygen was increased, no difference in final cell density was observed between spaceflight and normal gravity. Because motility has been suggested to affect how microbes respond to microgravity, we compared the growth of wild-type P. aeruginosa to a ΔmotABCD mutant deficient in swimming motility. However, the final cell densities observed with the motility mutant were consistent with those observed with wild type for all conditions tested.ConclusionsThese results indicate that differences in bacterial final cell densities observed between spaceflight and normal gravity are due to an interplay between microgravity conditions and the availability of substrates essential for growth. Further, our results suggest that microbes grown under nutrient-limiting conditions are likely to reach higher cell densities under microgravity conditions than they would on Earth. Considering that the majority of bacteria inhabiting spacecrafts and space stations are likely to live under nutrient limitations, our findings highlight the need to explore the impact microgravity and other aspects of the spaceflight environment have on microbial growth and physiology.

A Molecular Genetic Basis Explaining Altered Bacterial Behavior in Space

“…Ref. [55] also reported an increase in final cell count in space and that the difference between spaceflight and Earth controls could be minimized by the addition of growth-limiting substrates. Collectively, the enhanced growth condition explanation suggested to occur as a result of the proposed altered environmental factors in microgravity is further supported by the new gene expression data.…”

Increased growth rate and amikacin resistance of Salmonella enteritidis after one‐month spaceflight on China’s Shenzhou‐11 spacecraft

“…For instance, some microbial isolates were collected from astronauts and filter debris during orbital spaceflights on the International Space Station (ISS) (Checinska et al, 2015;Venkateswaran et al, 2014). It has been reported that the space environment can alter the microbial growth rate, virulence, and antibiotic susceptibility (Kim et al, 2013;Klaus & Howard, 2006;Mora et al, 2016;Rosenzweig, Ahmed, Eunson, & Chopra, 2014;Taylor, 2015;Urbaniak et al, 2018;Wilson et al, 2007). In addition, many studies have shown that the extreme environment of space plays an important role in dysregulation of the human immune system (Crucian et al, 2018;Kaur, Simons, Castro, Ott, & Pierson, 2005;Taylor, 2015).…”

Low-shear force associated with modeled microgravity and spaceflight does not similarly impact the virulence of notable bacterial pathogens

“…Furthermore, space microgravity produced thicker bioflims that exhibited motility-dependent, aberrant architectures (column and canopy structure) relative to the ground control cultures (Kim et al 2013a). Interestingly, when phosphate and oxygen levels were reduced, P. aeruginosa exhibited increased final biomass/enhanced growth during spaceflight (Kim et al 2013b). Whereas the contents of M9 salts diminished salmonellae hypervirulence in murine infections following spaceflight and phosphate was speculated to be the key factor (Wilson et al 2008), phosphate also positively influenced P. aeruginosa growth during spaceflight (Kim et al 2013b).…”

“…Interestingly, when phosphate and oxygen levels were reduced, P. aeruginosa exhibited increased final biomass/enhanced growth during spaceflight (Kim et al 2013b). Whereas the contents of M9 salts diminished salmonellae hypervirulence in murine infections following spaceflight and phosphate was speculated to be the key factor (Wilson et al 2008), phosphate also positively influenced P. aeruginosa growth during spaceflight (Kim et al 2013b). It seems that some spaceflight responses of various bacteria seem dependent on specific nutritional factors (e.g., the presence of phosphate).…”