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Can fermenting microbes save us from climate change?

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Clostridium-ljungdahlii Just as bacteria and fungi are methodically breaking down the millions of gallons of oil spewing into the Gulf of Mexico, microbes might help us with another uncontrolled emission due to human activity—carbon dioxide.


An anaerobic bacteria by the name of Clostridium ljungdahlii can ferment everything from sugars to simple mixtures of carbon dioxide and hydrogen—or even carbon monoxide and hydrogen (otherwise known as syngas). Keeping these bacteria away from oxygen (which could be toxic for them) when far from its home environment of chicken yard waste is a challenge of course, but industrial bioreactors might be one solution.


So German microbiologists have gone ahead and sequenced its genome—all 4.6 million base pairs (roughly 1/1000th the size of the human genome or more than four times the size of the synthetic genome created by scientists at the J. Craig Venter Institute). Turns out that C. ljungdahlii has a unique way of eating such simple hydrocarbon mixes—it involves reducing iron-sulfur proteins—and turning them into ethanol for growth. That unique method may make it easier to introduce foreign genes that can tune the CO2-transforming cellular production machinery to make the end product desired. For example, the German scientists showed how to insert genes to make C. ljungdahlii make butanol instead of ethanol.


"The synthesis capabilities of C. ljungdahlii from CO and CO2 are not limited to biofuels, but can be expanded to virtually every compound for which biological pathways exist or will be newly constructed," the researchers write in the June 28 Proceedings of the National Academy of Sciences, in which they unveil the genome. "This unique biotechnological approach will reduce dependency on crude oil, will fulfill industrial needs and, by doing so, could contribute to reducing the atmospheric greenhouse effect."


In fact, this could result in fuels that actually consume as much or more CO2 than they release back into the atmosphere (as long as the hydrogen isn't produced by cracking natural gas or a similar CO2-intensive method). Such efforts are not confined to one scientific team, of course, or even one bug. The list of candidates is long: Acetobacterium woodii, Desulfobacterium autotrophicum, Methanosarcina barkeri, Moorella thermoacetica, or the tweaked Eschericia coli currently churning out diesel for the company LS9. In fact, the list of companies pursuing microbiological approaches to carbon neutral fuel and chemical production is nearly as long: Coskata, INEOS Bio, LanzaTech, Qteros among others.


Regardless of what human tinkering does to them, such CO2 eaters are likely to find favorable conditions in coming years as concentrations of the greenhouse gas rise inexorably, thanks to the current human habit to burn fossil fuels.


Of course, there is another set of microbes that can address CO2 quite well, as well—algae (and other microscopic plants). Companies, scientists and even government agencies are pursuing that avenue as well (from Solazyme to DARPA) but so is nature. Eventually vast blooms of the single-celled plants might restore the planet to some semblance of the present climate. After all, that's why we enjoy an atmosphere with a nice comfortable amount of oxygen for us: 21 percent. Unfortunately getting back to the the current climate (which has been optimal for the emergence of human civilization) after a catastrophic climate change is likely to take the mighty microbes millions of years, at least.


Mankind may have started this climate change but it is algae that will finish it, like all the others. Indeed the meek—minute microbes—will inherit the Earth, one way or the other.

The views expressed are those of the author and are not necessarily those of Scientific American.

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