SUBSURFACE MICROBES

from EVOLVE, Autumn 2021

Microbes are incredible. They’re extremely diverse, with our current estimate being that there are an astounding one trillion species on Earth, which only makes up 0.001% of the entirety. Not only that, but some species boast unique abilities which challenge our way of thinking about life and its possibilities. These range from a species which can breathe uranium (betaproteobacteria) to one which can survive some of the most unforgiving conditions such as vacuums, radiation, cold temperatures, acid, and dehydration (Deinococcus radiodurans).

 

The deepest we have found microbes is 5km below the seafloor, where they live in small fractures in stone or deep-sea hydrothermal vents, often sharing close symbiotic relationships with invertebrates and crustaceans like crayfish, isopods and amphipods. These receive food in exchange for a type of haemoglobin which provides the bacteria with a source of oxygen and hydrogen sulphide necessary for their metabolism. Shockingly, even these seemingly inhospitable environments are estimated to support over 500 different species of marine organisms, but how do they survive? There’s very little oxygen, light, or much organic matter. So, what allows these bizarre microorganisms manage to live in some of the most unforgiving habitats? The answer is by working hand in hand with science. 

 

There is one specific type of microorganism which I think is one of the most interesting called Chemolithoautotrophs, which have adapted to survive off hydrogen, formate, sulphide and reduced metal ions (as suggested by their name — ‘Chemo’, meaning they use chemical means to gain energy, and ‘Litho’ which means they use inorganic matter). They have a very slow reproductive cycle, with many of them not having undergone a single cell division since the time of ancient Egypt. This means most have likely been around for far longer than many other organisms we know of. One of the many reasons this type of microbe is particularly fascinating is that it can gain energy from inorganic materials including ammonia, which is highly corrosive and thus dangerous to humans in high concentrations, and turn it into mineral deposits such as rust and pyrite (fool’s gold) along with a few other by-products. These microbes can also make carbon sources for themselves, which is shown by their name ‘autotroph’, meaning an organism capable of producing its own carbon. But what’s even more exciting is the fact that these microbes are extremely good at converting carbon dioxide into oxygen.

 

Carbon dioxide is stored under the Earth’s surface, mostly in subduction zones. But how is it that we don’t see it escaping into the atmosphere? The answer is, as you may have predicted, microbes filter it out and convert it into minerals, which is important due to the Earth’s ongoing carbon problem. In 2019 alone, about 43.1 billion tons of carbon dioxide was emitted into the atmosphere from human activities. The state of our atmosphere has become a serious issue, one which scientists, engineers, and organisations such as the Carbon Trust are trying to solve. So now you ask, why haven’t people thought to use microbes’ abilities to help solve our problem? Surely someone must have come up with the idea to use chemolithoautotrophs’ incredible ability to take up carbon dioxide from their surroundings as a way of reducing our carbon emissions. Unfortunately, as mentioned before, these organisms are incredibly slow to reproduce. So, unless we find a way to artificially create more, it is unlikely that there will be enough to make a significant change. 

 

Still, the world is full of microbes. They are tiny organisms that all look like brightly dyed blurs under a microscope which, despite being so insignificant in size, play a vital role in how our planet works. They possess some of the most incredible abilities, have the potential to be the root of so many amazing scientific discoveries, and could help us solve some of the biggest issues we currently face.

Written by Sofia