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November 18, 2013

Bacteria: The Evolution of Recycling and the Real Stewards of the Earth

by Seth Commichaux
I walked the halls, the magnificent halls
The marble floors were always clean
I never thought that while I slept
Someone was sweeping behind the scenes
When I was born, the stage was set
I only needed to stand and take my place
It didn't hit me hard 'til late
That my life was but one leg in an endless relay race
As I aged, I foresaw Armageddon
But it really was my life reaching an end
And all the trash I never cleaned up
Would be put in order when I laid down to sleep again

Before 1936, PCP (pentachlorophenol) didn't exist in nature--at least not anywhere we knew of.  PCP was used to protect timber from fungal rot, but it has also been used as an insecticide, herbicide, algaecide and disinfectant.  In the environment it has a life from a few hours long up to a decade or more depending on the conditions.  In sunlight it breaks down rapidly in a process called photolysis, but when in underground water supplies or in the soil it can take many years to break down.
"Short-term exposure to large amounts of PCP can cause harmful effects to the liver, kidneys, blood, lungs, nervous system, immune system, and gastrointestinal tract.  Elevated temperature, profuse sweating, uncoordinated movement, muscle twitching, and coma are additional side effects.
Contact with PCP (particularly in the form of vapor) can irritate the skin, eyes, and mouth. Long-term exposure to low levels such as those that occur in the workplace can cause damage to the liver, kidneys, blood, and nervous system.  Finally exposure to PCP is also associated with carcinogenic, renal, and neurological effects." (cited from: http://en.wikipedia.org/wiki/Pentachlorophenol)

The use of and therefore the release of PCP into the environment has declined over the years because of its toxicity, but it is still used by wood treatment plants.  In the USA it is still used, mostly, to treat railroad ties and utility poles.  Because of its toxicity and because of the potential that it can remain in the environment for years it has been a chemical of concern and there are regulations on the amounts that can be in drinking water. 

For many years it seemed like sunlight or time were the only things that could degrade PCP, but as years passed a recycler of PCP evolved.  A bacteria called Sphingobium evolved the metabolic capacity to breakdown PCP.  Because of mutations in enzymes that were originally geared to breakdown amino acids the bacteria could exploit the new resource.  As time passed, natural selection favored new mutations that increased the efficiency in the degradation of PCP. 

What's remarkable to me about the bacteria, Sphingobium, is that it evolved to eat and derive nutrients and energy from a chemical invented by humans.  Evidently, Life has a much underappreciated capacity for ingenuity.
People have a way of discounting bacteria as just damned germs, but the truth is that bacteria probably play a bigger role in maintaining the habitability of Earth than any other group of organisms.  They are the recycling and sanitation crew for the world.  Not to mention all of the symbiotic services they provide within the bodies of multi-cellular organisms.  Bacteria are ubiquitous on Earth.  They live in rocks, in boiling springs, miles under the ocean floor, floating high in the atmosphere, inside animal guts and plant roots, inside the ice of glaciers, don't be surprised if they're found drifting in space.  They are the most metabolically complex and diverse organisms.  Every attempt that humans have made to undermine their abilities has failed.  Chemicals, radiation, medicines, vaccines, viruses, gene manipulation, catalysts, etc. have all been employed and time-after-time bacteria have evolved resistance. 
On the other hand, many human screw-ups have seen the arrival of hoards of microscopic heroes.  Bacteria were found that could eat crude oil who are now regularly hired in the wake of spills.  Many chemicals released into the environment with little foresight, which proved to be toxic to humans and that were thought to be environmentally invincible, have inspired the geniuses of nature to evolve new appetites.  Many bacteria have evolved to degrade the pollutants we've created.  More and more, in the scientific literature I see references to bacteria that are being discovered who can degrade the various plastics that we've allowed to trash our oceans and lands.  Bacteria put the superheroes of the movies to shame.  Because unlike saving the world from imaginary evils in a fantasy, bacteria are evolving to eat our pollutants and might just save humanity from itself in reality.  Pollution is a relative term, for though the pollutants we create might be detrimental to ourselves and to other plants, animals and microbes, there always seems to be someone who finds a treasure in the junk we dispossess.  The trash we've littered the world with has created a new niche that calls like a prize to any organism that can evolve to exploit it.  More than likely the winner will be a bacteria, but a question stands and glares at us in the face.  Can we really wait on the evolution of a cleaning crew for every mess we make?  I think not, but then again if climate change, pollution or nuclear fallout are the end of humanity we can always take comfort in the idea that there'll be bacteria that survive it to continue the adventure of evolution.  

-Seth Commichaux
Sources Cited:
Evolution: Making Sense of Life.  Carl Zimmer, Douglas J Emlen.  2013.
Life in the "Plastisphere": Microbial Communities on Plastic Marine Debris.  Erik R. Zettler, Tracy J. Mincer, Linda A. Amaral-Zettler.  Environmental Science and Technology.  Accepted June 7, 2013.

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