How is it that bacterium can survive a vacuum like outer space?
In: Biology
A couple things kill you in space. The obvious thing is a lack of oxygen. Humans need a lot of oxygen, bacteria need a lot less (which should make sense – they’re a lot smaller). Some bacteria don’t use oxygen *at all*. They still need *something* to allow chemical reactions to give energy, but they can often carry a reserve of that something with them and may be able to use energy in the environment to undo the reaction and reuse those chemicals.
Another thing that kills you in space is the lack of pressure. The Earth’s atmosphere weighs a *lot*. We don’t “feel” that weight because our insides are at the same pressure. The inside is pushing *out* as hard as the out is pushing *in*, and they are balanced. In space there is essentially nothing pushing in at all, but your insides are still pushing *out*, which is, you know, bad. Liquids also boil at low pressures because there’s nothing squeezing them together to stay liquid, so the water in your body tries to not be water anymore, which again is…bad. Your cells end up expanding like balloons, often until they burst. Many (but not all) bacteria have a stiff cell wall around them to protect them. That also holds them together so they can’t burst from the negative pressure trying to expand them.
If you’re in shade, there’s nothing to hold onto heat so you get frozen. Some extremophile bacteria have special proteins or sugars that prevent the water in them from crystalizing – basically, they have built-in antifreeze and can keep going. The side facing the Sun has no protection against the intense sunlight so you get super mega sunburned. Even extremophile bacteria can’t survive in sunlit parts of space for very long, but some have special protections against radiation that allow them to withstand it for a brief period. They need that in the shade, too, because there’s a lot of radiation flying around in space from all directions with no atmosphere to remove it.
Mostly, though, most bacteria that “survive” in space do so in a special encapsulated spore form that kind of shuts down and stops really living for a while. Bacteria do this all the time on earth to survive unfavorable conditions, like if they need a wet environment and it gets too dry. They build an even stronger shell around themselves and almost all of the internal chemistry of the cell stops. They are super protected from most dangers this way. When the environment gets back to something they can live in, they dissolve the protein shell and get back to truly living. Very few kinds of bacteria can survive in space outside of this spore form.
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