The researcher studied the growth of Bacteria in space experiments under microgravity conditions have been found to undergo unique physiological responses, ranging from modified cell morphology and growth dynamics to a putative increased tolerance to antibiotics. To further characterize the responses, this study investigated the transcriptomic response of Escherichia coli to both microgravity and antibiotic concentration. 

E. coli was grown aboard International Space Station in the presence of increasing concentrations of the antibiotic gentamicin with identical ground controls conducted on Earth. They conclude that the increased antibiotic tolerance in microgravity may be attributed not only to diminished transport processes.

But also to a resultant antibiotic cross-resistance response conferred by an overlapping effect of stress response genes. Among the many risks, astronauts will face as they venture into missions beyond lower Earth orbit are those that arise from microbial responses to spaceflight.

Immune dysfunction associated with spaceflight conditions can potentially increase the susceptibility of crew members to pathogenic bacteria in extended space missions. Spaceflight has been shown to promote biofilm formation in bacteria, which may pose challenges involving biofouling, corrosion, the contamination of water sources, and increased bacterial virulence.

In this study, they investigated the changes in the transcriptome of E. coli cultured on the International Space Station (ISS) when challenged with different concentrations of the antibiotic gentamicin sulfate, compared to controls grown on Earth. The higher tolerance of E. coli in microgravity to gentamicin is most likely due to a combination of two factors:

(1) The lower effective dose of antibiotic reaching the cell due to transport limitations

(2) The cross-resistance conveyed by the cell’s response to the acidic and nutrient-starved local environment in microgravity, a secondary consequence of reduced transport.

Through the analysis of RNAseq data for E. coli challenged by both a microgravity environment and varying concentrations of the antibiotic gentamicin, we note several key observations that contribute to the picture of the bacterial adaptive response to antibiotics and provide new questions going forward in future research. 

Further, they identify two toxin-antitoxin system genes, as well as the signaling molecule indole, which likely has a significant role in the adaptation of bacteria in space to the unique combination of stress it is experiencing. More research into exactly how these systems are contributing could help to fill in missing pieces in the understanding of bacterial resistance.

The data and conclusions presented by this study pose a series of questions regarding the complex stress regulator networks in E. coli that can be probed in the future to help discern just how microgravity is affecting bacterial responses to drugs. Additionally, we believe that by building on these findings, they will be able to provide new insights for the design of antibiotics that perform effectively in a variety of different environmental conditions.