An Earth Day Shout-out to Microbes
So another Earth Day has come and gone. How did you spend yours? If you spent the entire day asleep, you used about half a kilogram of oxygen. Since I assume that you are alive and kicking, you probably consumed more oxygen than that. If you went about your normal business during the day, you probably consumed almost 1 kg of oxygen (~0.8 kg). On the other hand, if you decided to run a marathon before sitting down this evening to read bLogPhase, you may have needed a hefty supply of over 7 kg of oxygen. Regardless of how you spent the day, I would encourage all readers of bLogPhase to celebrate Earth Day 2016 with a shout-out to microbes who made the oxygenation of our planet possible. An Earth without microbes would be, in Shakespeare’s phrase, “dull, stale, flat, and unprofitable.”
I geared up for my Earth Day 2016 rereading Paul Falkowski’s excellent book Life’s Engine: How Microbes Made Earth Habitable. In a rigorous and yet very accessible way, Falkowski describes exactly how microbes drove the oxygenation of the Earth. Our planet runs on a global water cycle which involves splitting water to form oxygen through photosynthesis, and resupplying water, through respiration. The first microbes on Earth were not able to split water but with the evolution of blue-green algae, the Cyanobacteria, here were organisms going about their business, splitting water and producing a new waste product—oxygen. And with that, Cyanobacteria changed the Earth forever. Joe Kirschvink, a biologist from Caltech, calls the Cyanobacteria “the microbial Bolsheviks” who radicalized Earth long before and more profoundly than the Russian Revolutionaries.
If microbes made Earth habitable, microbes also keep Earth habitable with a myriad of fundamental contributions, all thanks to their boundless enzymatic armamentarium. Recently, another of these startling microbial earth-shaking adaptations caught my attention—the discovery of a new bacterium, Ideonella sakaiensis, which can feed exclusively on plastics by degrading poly-ethylene terephthalate (PET), the material of the classic plastic bottle! Isolated in a plastic bottle recycling plant in Japan, Ideonella has developed two enzymes which can metabolize the stable, yet very simple ester bond in the PET polymer. Talk about a potentially useful discovery.
Every year we produce over 300 million tons of plastic, of which only ~14% is recycled, and over 55 million tons of the total plastic is PET. This otherwise stable product is produced in such quantities and biodegrades so slowly that it now poses a special threat the environment especially the oceans that some have proposed that all plastics should be labeled “hazardous material” because of their effects on animals and humans. But here a microbe is suggesting another way to envision plastics, use its carbon as the sole source of energy. And imagine if we could then, for example, isolate and reuse the terephthalic acid from the microbial metabolism to produce new polymers!
Not surprisingly, the I. sakaiensis study caught the attention of the world’s news media. Here was a new bacterium with intriguing new enzymes and a new biochemical degradation mechanism that could eat mountains of PET plastic bottles. For microbiologists, the ability of microbes to metabolize plastics was not news. It goes beyond milk bottles. For example, look at the recent discovery in the gut of the mealworm insects (Tenebrio molitor) of a new strain of Exiguobacterium that is able to degrade polystyrene. Scientists showed that indeed Exiguobacterium confers the ability of Tenebrio to feed itself solely on polystyrene; they used antibiotics such as gentamicin to show that the insect can no longer biodegrade polystyrene without the essential help of Exiguobacterium, leaving the mealworms unable to survive solely on that diet. Personally, I have infinite respect for microorganisms that can live on polystyrene but I prefer to keep my very own microbiome on a tastier gnocchi diet.
Earth Day is about celebrating our “blue green” planet, teeming with oxygen-loving life, thanks to our microbial friends who filled the atmosphere with their waste oxygen. It should be a special day for microbiologists who know how our science could ease some of our poor planet’s troubles. Our science constantly turns up new species, new mechanisms, and new ways to repair some of the damage we’ve done with our waste, including plastic pollutants. This Earth Day, I am reminded of the legendary movie The Graduate where a young Dustin Hoffman is cornered at his graduation party by a family friend who gives him one word of career advice: “Plastics!” On Earth Day 2016, I have one word for today’s graduates—“Microbes!”