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Bugs in space! Using microgravity to understand how bacteria can cause disease

Space may be the final frontier, but it’s not beyond the reach of today’s biologists. Scientists in all areas of biology, from tissue engineering to infectious diseases, have been using the extreme environment of space to investigate phenomena not seen on Earth. The National Aeronautics and Space Administration (NASA) has conducted research in the life sciences for almost 50 years. Some of this research relates directly to human space exploration, while other projects investigate broader scientific questions related to human health and disease.

In the early 1990s, NASA started flying living cells on their space shuttles to investigate how cells respond to the rigors of spaceflight. Several different types of human cells were flown in space, with each showing various changes in size, shape, growth rate, and other behaviors. At the same time, NASA built a vessel capable of mimicking the microgravity environment of space. While not able to fully recapitulate all the environmental changes brought on by spaceflight, the rotating wall vessel (RWV) provides an environment of low-shear modelled microgravity (LSMMG), which is sufficient to induce many of the changes seen in space.

The RWV was originally designed to help researchers grow cells in three-dimensions. When human cells are grown in the laboratory under normal conditions, they form a flat sheet, with no overt structure. In contrast, cells grown in the RWV come together to form mini-organs or organoids, with similarities to normal human tissue. Organoids have been created for several human tissues, including lung and bladder, although gut organoids are the most advanced. Organoid models have many uses in research, from understanding basic cellular interactions to investigating drug toxicity and infection.

The techniques and equipment developed for the study of human cells in space have been used by microbiologists to study the impact of spaceflight and microgravity on bacteria and fungi. In early spaceflight experiments, researchers examined the effect of low gravity on common laboratory bacteria. Surprisingly, there was a trend towards increased growth rate and resistance to stress in bacteria grown in space. While researchers couldn’t determine how the bacteria were able to sense gravity, their ability to do so opened up a new field of bacterial research.

Image credit: Stapylococcus aureus bacteria escape. Public Domain via Wikimedia Commons
Stapylococcus aureus bacteria escape by National Institutes of Health. Public Domain via Wikimedia Commons.

Over the following years, these experiments were repeated with some important findings. Two different bacterial species often associated with hospital-acquired infections, Staphylococcus aureus (Golden Staph) and Pseudomonas aeruginosa, showed an increased ability to persist as a biofilm after growth in LSMMG. Biofilms are slime-like masses of bacteria that adhere to surfaces and protect the bacteria from external pressures such as disinfectants, manual cleaning, and desiccation. Biofilms are especially important in the hospital setting, where bacterial persistence can be problematic. S. aureus grown in LSMMG also showed increased resistance to antibiotics.

Even more intriguing were the spaceflight experiments completed using the gastroenteritis-causing bacterium Salmonella. In two separate experiments, researchers showed Salmonella grown in LSMMG or in space were more deadly in mice than bacteria grown on Earth. These bacteria were not only able to sense the change in gravity, but changed their behavior to become more lethal. It’s unclear why bacteria have evolved this mechanism. However, some researchers have suggested that within the intestines, there is an area close to the microvilli that displays microgravity-like low shear. As this is also where Salmonella likes to invade their host, it is possible the bacteria use this microgravity-sensing ability to determine the correct moment to attack.

Various studies have shown the utility of spaceflight research in understanding the world we live in, and the unforeseen advances that can be made by utilizing space technology in biological research. While on the face of it, this research may seem obtuse, learning how and why cells respond to microgravity may lead to better therapeutics and preventatives for important diseases.

Featured image credit: Cosmos by insspirito. CC0 Public Domain via Pixabay.

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