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

Kim W, Tengra FK, Shong J, Marchand N, Chan HK, Young Z, Pangule RC, Parra M, Dordick JS, Plawsky JL, Collins CH - BMC Microbiol. (2013)

Bottom Line: 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.These 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical & Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. ccollins@rpi.edu.

ABSTRACT

Background: Abundant 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.

Results: Here, 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.

Conclusions: These 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.

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Comparison of plate counting and FCM measurements of microbial growth during spaceflight. Wild-type P. aeruginosa was cultured under normal gravity (black bars) and spaceflight (gray bars) conditions in mAUMg containing 5 mM or 50 mM phosphate. (a) The number of viable cells in unfixed samples was measured by plate counting. (b) The number of cells in fixed samples was measured by flow cytometry (FCM). Statistical differences between normal gravity and spaceflight for each experimental condition were analyzed by one-tailed t-test: *p < 0.05. Error bars indicate SD; N = 3.
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Figure 2: Comparison of plate counting and FCM measurements of microbial growth during spaceflight. Wild-type P. aeruginosa was cultured under normal gravity (black bars) and spaceflight (gray bars) conditions in mAUMg containing 5 mM or 50 mM phosphate. (a) The number of viable cells in unfixed samples was measured by plate counting. (b) The number of cells in fixed samples was measured by flow cytometry (FCM). Statistical differences between normal gravity and spaceflight for each experimental condition were analyzed by one-tailed t-test: *p < 0.05. Error bars indicate SD; N = 3.

Mentions: While we anticipated data from plate counting and FCM measurements of final cell concentration would yield similar results and reinforce each other, our analysis showed very different results from the two methods under a number of conditions. This discrepancy between the two methods was most pronounced when cells were cultured in mAUM containing 2 mM glucose (mAUMg). In mAUMg, FCM data indicated that growth during spaceflight led to increased cell numbers compared to normal gravity, while plate counting data showed no difference in the final cell density between spaceflight and normal gravity (Figure 2). However, when the phosphate concentration was increased from 5 to 50 mM (mAUMg-high Pi), FCM and plate counting data exhibited similar trends (Figure 2).


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

Kim W, Tengra FK, Shong J, Marchand N, Chan HK, Young Z, Pangule RC, Parra M, Dordick JS, Plawsky JL, Collins CH - BMC Microbiol. (2013)

Comparison of plate counting and FCM measurements of microbial growth during spaceflight. Wild-type P. aeruginosa was cultured under normal gravity (black bars) and spaceflight (gray bars) conditions in mAUMg containing 5 mM or 50 mM phosphate. (a) The number of viable cells in unfixed samples was measured by plate counting. (b) The number of cells in fixed samples was measured by flow cytometry (FCM). Statistical differences between normal gravity and spaceflight for each experimental condition were analyzed by one-tailed t-test: *p < 0.05. Error bars indicate SD; N = 3.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 2: Comparison of plate counting and FCM measurements of microbial growth during spaceflight. Wild-type P. aeruginosa was cultured under normal gravity (black bars) and spaceflight (gray bars) conditions in mAUMg containing 5 mM or 50 mM phosphate. (a) The number of viable cells in unfixed samples was measured by plate counting. (b) The number of cells in fixed samples was measured by flow cytometry (FCM). Statistical differences between normal gravity and spaceflight for each experimental condition were analyzed by one-tailed t-test: *p < 0.05. Error bars indicate SD; N = 3.
Mentions: While we anticipated data from plate counting and FCM measurements of final cell concentration would yield similar results and reinforce each other, our analysis showed very different results from the two methods under a number of conditions. This discrepancy between the two methods was most pronounced when cells were cultured in mAUM containing 2 mM glucose (mAUMg). In mAUMg, FCM data indicated that growth during spaceflight led to increased cell numbers compared to normal gravity, while plate counting data showed no difference in the final cell density between spaceflight and normal gravity (Figure 2). However, when the phosphate concentration was increased from 5 to 50 mM (mAUMg-high Pi), FCM and plate counting data exhibited similar trends (Figure 2).

Bottom Line: 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.These 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Chemical & Biological Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180, USA. ccollins@rpi.edu.

ABSTRACT

Background: Abundant 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.

Results: Here, 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.

Conclusions: These 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.

Show MeSH