Bacteria are everywhere. In your mouth, in your bed, at the bottom
of the sea, underground, anywhere you can name that isn't really hot,
really acidic or otherwise too hostile for life. But how did they get
there? Some animals are found all over the place but they have stuff
like wings and legs and Double Decker buses, bacteria don't have any of
that!
On a small scale, they can kind of swim along with big floppy
oars/propellers called flagellae, but I'm thinking bigger than that. Of
course in the sea they can just float around on the current hoping they
don't get eaten by whales, but on land? How did they get to Australia?
Or Hawaii?
The key to this is partly their numbers. Being microscopic is less
of a problem when there's billions of you, so while individual cells
won't make the trip up a mountain or even across the floor the colony as
a whole might spread there just by multiplying. Plus, due to their
impressive rate of reproduction, even single cells getting to a new
place can lead to it being colonised. Bacteria on migrating birds for
example can be transferred to new lands. But one of my favourite routes
of global bacterial transmission is via the clouds!
Clouds are full of bacteria. In fact, it's been shown that above
about four degrees Celsius dust particles can't gather water vapour to
form cloud particles, and bacteria are much more likely culprits. Just
like marine bacteria float on ocean currents, airborne cloud bacteria
can be carried all over the world!
I used to work in a lab looking for thermophilic bacteria in soil
samples from the UK. These bugs were needing temperatures of sixty to
seventy degrees, so why were they in cold British soil? There's a
weather phenomenon in Britain and Europe where everything gets covered
in sand blown up from the Sahara desert, and the same winds can carry
thermophiles to distant lands! I was working with Geobacillus, which can
hibernate in spores for a huge amount of time, so they just kept
getting added to the soil by the wind and rain. They were just sitting
there for me to find!
Don't worry too much though: any bacteria in the rain are in too
small numbers to cause you any harm. After all, most bacteria are
friendly!
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