When times get “trying” here on planet Earth ECIC wishes she was on Pluto with her cats, her rules and no people! But she may not be alone!! The newest research suggests that bacteria can survive in the hostile environment of space; maybe the dream of living on Pluto with remote “homeworking” for a Consultant Microbiologist might be a reality (our hospital computer system is called Enterprise after all!)
No, No, No, stick with me!!! It’s true, those pesky microorganisms have been found to survive on the outside of the ISS (International Space Station). There’s even a named theory… the theory that living organisms can survive and transfer through space is known as “panspermia”.
However it’s all very well doing experiments on Earth to try and predict what would happen in space, or wrapping bacteria up in protective shells, but the only real way of finding out whether bacteria can survive in space is to put naked colonies of bacteria into space with no protection. But did you know it’s illegal to do that!
Legalities of space
It is actually illegal to send bacteria off into space. There are rules about this! In October 1967 the “Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies” came in to force. What a mouthful! It is now known as the “Outer Space Treaty” and essentially it forms the basis of international space law. Part of this Treaty prohibits the deliberate or accidental release of microbes onto other planets and their moons. This means that we cannot send bacteria into outer space to see if they grow.
However to get around this “technicality” and test the theoretical possibility of panspermia Japanese scientists came up with an elegant experiment whereby bacteria could be attached to the outside of the International Space Station (ISS) and exposed to the environment of low Earth orbit for prolonged periods of time. This would then allow them to use their results to help predict whether bacteria can survive in space.
The scientists chose two environmental Gram-positive cocci called Deinococcus radiodurans and Deinococcus aerius. The first bacterium sounds particularly promising as radiodurans implies it is very good at resisting radiation damage.
Back in 2015 the SpaceX rocket took 6 aluminium plates of dried pellets of bacteria to the ISS. Three plates were connected to a handrail outside of the Japanese Experimental Module by a robotic arm and 3 plates were kept in a sealed plastic bag in the ISS. A further 3 plates were kept back on Earth. Plates were removed and returned to Earth to be tested at yearly intervals to see if the bacteria in the dried pellets had survived their space mission.
Can bacteria survive in space?
The results of these experiments are amazing. What they have found is that D. radiodurans was able to survive as well in space as on Earth provided the pellet of bacteria was about 500microM thick… that’s only half a millimetre; the experiment tested 100, 500, 1000 and 1500 microM thickness but 100 wasn’t enough. D. aerius actually needed 1000 microM to survive. Although survival decreased over time this was the same whether the sample was on Earth or in space, and both bacteria could be readily recovered after the 3 years.
As an aside the samples that did worst were the samples inside the ISS and it is theorised that by keeping them in a plastic bag inside the station where these bacteria were exposed to high humidity caused an issue; “house plants” can be the trickiest to look after after all!
So how did these bacteria survive in space?
There are some bacteria that are known as extremophiles (liking extreme environments) which can survive brief periods of exposure to extreme environments, some of which simulate outer space conditions such as high radiation, large fluctuations in temperature and living in a vacuum. These include Bacillus subtilis, Thermus aquaticus, Aspergillus terreus and Cyanobacterium chroococcidiopsis! In fact bacteria that can survive in a vacuum without oxygen are a very common phenomenon and we see them every day in the clinical laboratory e.g. E. coli, S. aureus, Clostridium spp.
Apparently the temperature outside of the ISS can swing between -150oC and +120oC depending if the ISS in bathed in sunlight or in shadow. The main problem here for bacteria isn’t the cold, we regularly store bacteria in the lab at -80oC to preserve them so -120oC probably isn’t too bad, but it’s rather the heat and the temperature change. The reason that our space bacteria survived the temperature swings is that there was no moisture. The pellets were completely dry; no moisture, no ice, no freezing/thawing which means the cells aren’t damaged.
But the big problem, and the main reason for the Japanese experiment, was to see if the bacteria could survive being exposed to radiation for long periods of time.
Once you step outside of our atmosphere the amount of radiation exposure increases dramatically. Countries that send astronauts into space take this problem very seriously and try to minimise the risk of radiation induced cancer as much as possible by shielding astronauts inside protective boxes (the ISS), reducing the astronauts’ time in space (6 months) and using medication such as antioxidants. Unfortunately for the bacteria attached to the outside of the ISS none of these “employee” protective measures were taken… this was done on purpose! Which also begs the question do bacteria – living organisms that move, perspire and reproduce - have Rights?!? Which then poses the question “should we be killing bacteria with antibiotics!?!” [Move on Editor Chief in Charge!!]
So how were the bacteria protected from radiation damage?
- Firstly the bacteria created their own “shield”; the outer layer of bacteria died (and became “bleached” by UV light) forming a barrier of dead cells between the surface and the underlying bacteria, hence thicker pellets of bacteria survived better.
- Secondly the bacteria have enzymes that are able to repair radiation damaged DNA. Most bacteria have 1 of these enzymes, humans have 2, but D. radiodurans has an astounding 10! These enzymes were able to repair radiation damaged bacterial DNA in the shielded bacteria but were insufficient to repair the damage to their outer layer.
So amazingly, bacteria were able to survive the harsh environment of space for over 3 years. Based on their results the scientists have estimated that the same bacteria could have survived 15-45 years attached to the ISS, and possibly 2-8 years in outer space. This is potentially enough time to travel between the Earth and Mars! But probably not Pluto, maybe my Microbiology job has just been withdrawn.
But before you all go thinking that we are all descended from aliens a word of caution. There are still some massive big stumbling blocks in the way of bacteria transferring between planets and the most important is atmosphere.
The force, and therefore energy, required to shoot a collection of bacteria (or rocks containing bacteria) from a planet into space would be very large. This force is likely to produce heat and this heat would probably sterilise whatever was thrown into space. In addition any bacteria or rocks entering into an atmosphere of another planet would be exposed to equally high temperatures. As a space craft returns to Earth the friction caused by our atmosphere raises the temperature of the space craft to over 1600 degrees Celsius and no bacteria or other living organism can survive that extreme environment. When you see a shooting star what you are seeing is a meteor burning up in our atmosphere, entering meteorites (meteors that make it to the ground) need to be at least the size of a marble to reach the surface of the Earth, and even then the temperature exposure would be too much for bacteria to survive.
Perhaps the most important lesson we can learn from the Japanese experiment is that we might actually “litter” our universe with contamination from people or equipment we send in to space. Or any bacteria on the outside of a space crafts may well survive the journey and pollute the destination with Earth germs. We’ve already made a mess of this planet by transporting micro-organisms over much shorter distances… let’s make sure we don’t make the same mistakes again and cause an Interstellar Pandemic!!!
DNA damage and survival time course of Deinococcal cell pellets during 3 years of exposure to outer space. Kawaguchi Y, Shibuya M, Kinoshita I, et al. Frontiers in Microbiology August 2020 Vol 11; 1-11