We know bacteria will accompany humans as we continue our exploration of space, and this makes it all the more important to study how bacteria adapt to near weightless conditions.
A number of studies have been done, including a “citizen-science” study conducted in 2015 that wanted to see if bacteria found on everyday surfaces here on Earth would grow in space.
More recently, though, scientists have used contrast light microscopy and focused ion beam/scanning electron microscopy, 3-D imaging, and Transmission Electron Microscopy, along with statistical analysis tools like the Welch’s test and the Brown–Forsythe statistical test – giving them a clearer understanding of what does happen to bacteria at the genetic and cellular level.
In June 2017, scientists from the University of Houston in Texas discovered that not only do some bacterial strains grow in low or zero-gravity but they also mutate.
This raised serious concerns for extended voyages into space and could put space travelers’ health at risk. Additionally, the formation of biofilms could either gum up delicate machinery on a spacecraft or short circuit the electrical systems.
Phenotypic changes in E. coli cultured in space
Published on August 28 in the journal, Frontiers in Microbiology, the new study is the first to track the physical changes in bacteria, specifically the E. coli strain, after exposure to antibiotics.
In the experiment conducted aboard the International Space Station (ISS), researchers with Colorado University, Boulder’s BioServe Space Technologies exposed cultures of E. coli bacteria with various doses of the antibiotic gentamicin sulfate.
Gentamicin sulfate has proven to be quite effective at killing E. coli infections here on Earth, but in the confines of the ISS, there were some very surprising, and somewhat scary, results. Instead of killing the cultures, the addition of the antibiotic caused a “13-fold increase in bacterial cell numbers and a 73 percent reduction in cell volume size,” according to Gizmodo.
A control group of experiments on Earth, done at the same time and in the same way showed the bacterial cultures were killed with the addition of the antibiotic. The researchers say the dramatic “shape-shifting” exhibited by the bacterial cultures in space is probably what helped them to survive.
Another observation by researchers was the difference in the bacterial colonies in liquid culture medium on Earth compared to the colonies in the same culture medium in space. On Earth, the cultures remained homogeneously distributed throughout the liquid medium, while in space they tended to form a cluster, leaving the surrounding medium visibly clear of cells.
This phenomenon is particularly important because it suggests this cell aggregation behavior may be associated with enhanced biofilm formation observed in other spaceflight experiments.
It was also discovered that some of the E.coli cells produced small capsules, known as membrane vesicles, on the outside of their cell walls, with researchers theorizing this action could help in facilitating the infection process.
“Both the increase in cell envelope thickness and in the outer membrane vesicles may be indicative of drug resistance mechanisms being activated in the spaceflight samples,” said UC Boulder microbiologist Luis Zea, who lead the study, in a statement. “And this experiment and others like it give us the opportunity to better understand how bacteria become resistant to antibiotics here on Earth.”
The research paper also mentions a decrease in cell size in microgravity has also been reported for a fungal organism: Candida albicans. Crabbé et al. (2013) determined that C. albicans cultured in space had 70 percent of the surface area of their matched Earth controls,
