In recent years bacteria have proven their ability to survive in the harsh environment of outer space. NASA has conducted many experiments after finding the presence of bacteria on the outer surface of the international space station. It is not yet known what causes these extreme genomic changes in microorganisms, it is thought high amount of radiation plays more of a role than microgravity.
Understanding how bacteria adapt to space ultimately helps to further understanding on how bacteria mutate and how this can be applied to future long-term space travel. To mark International Astronomy Day we look into the effects of microgravity on bacteria and how this can contribute to space travel.
Findings on Bacteria in Microgravity
Research has shown bacteria are able to undergo the following changes in microgravity:
- Increased rate of mutations that lead to permanent genomic changes
- Improved biofilm formation capability
- Increased production of secondary metabolites e.g toxins
- Thicker cell envelope
- Increased conjugation efficiency
- Increased virulence in some cases
Research into E. coli has shed some light on the impacts of microgravity on the species and found it replicated faster than a control sample under earth conditions. The study has shown the strain of E. coil acquired 16 genomic mutations and grew 3 times the number of colonies as the control E. coli strain. The cells also showed improvement in biofilm formation which could pose a potential threat to the astronauts who already have a compromised immune system in space. The study found E. coli retained 72% of the genomic changes they acquired in microgravity leading to permanent genetic advantages. Despite these mutations E. coli was still susceptible to antibiotics, despite advanced growth.
It is thought bacteria adapt and enter a state of starvation due to lack of carbon sources and increase expression of genes relating to carbon and nitrogen starvation. Experiments conducted on E. coli have shown it rapidly increased the rate of transcription of cells in order to widen its search for carbon sources, this may provide insight into the benefits of organisms in microgravity increasing their biofilm formation.
Experiments have led to the discovery of a bacterium called Deinococcus radiodurans which is a type of bacteria that known as a polyextremophile, meaning it can survive in two or more extreme environments. D. radiodurans is able to survive gamma radiation exceeding 1,500 kilorads without any cell death or mutations; this is extraordinary as E. coli cells will die in the presence of 6 Kilorads or less. Additionally, D. radiodurans can withstand high amounts of UV light and exposure to oxidising agents.
It has multiple copies of its genome which enable it to quickly repair damaged chromosome sections. It does do by a two-step mechanism. The first is by reconnecting chromosome fragments via single strand annealing. The second step involves repairing damage to the double stranded structure by homologous recombination.
Deinococcus radiodurans was sent to the international space station as part of an experiment to see if could survive the intense atmospheric radiation on the space station. Incredibly, when it was returned to earth it was still alive after 3 years. This this opens up many possibilities for potential research and gives us an insight into the types of bacteria that can survive in space and other planets like Mars.
The Future Outlook
Whilst most bacteria develop extremely advantageous mutations in microgravity, they can also be used as a potential food source for astronauts. Spirulina is a powder form of a type of a cyanobacterium called Arthrospira platensis, which was recently used as a food supplement for astronauts. It is highly nutritious with a high protein content (of up to 70%) and only a small amount of Spirulina contains the nutritional equivalent of 1,000 grams of fruit and vegetables. Research is still ongoing to see whether it could grow in space, as it would provide ongoing nutrition and could open opportunities for life on Mars.
As we could not live without bacteria on Earth neither in space, testing and research from bacteria adapting to space will help scientists understand the spaceflight environment’s effects on microbial evolutionary processes.
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