For the next session (Tuesday 4th March, 8pm GMT) we will be discussing the following paper: Effect of spaceflight on Pseudomonas aeruginosa final cell density is modulated by nutrient and oxygen availability available from the following link


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

Discussion points?

Was the paper well written?
Were the methods used appropiate?
Were the experiments carried out adequately?
What else can be done?