Microbial investment

The search for greener alternatives to fossil fuels has led to a major investment in a microbe that converts plant matter into ethanol.

Dubbed the “Q microbe,” the bacterium has been the focus of University of Massachusetts Amherst microbiologist Susan Leschine’s work for the past decade. Now it’s taking centre stage at SunEthanol, a new Amherst, Massachusetts-based biofuels technology company.

Noted for its appetite for all things cellulose – including switchgrass, wood pulp and corn plant waste – the bacterium is highly efficient at converting biomass to ethanol. And it does so in a carbon-neutral process that doesn’t require the additional enzyme treatments usually accompanying bioethanol production.

SunEthanol recently received millions of dollars in funding from several venture capital funds and other investors, including VeraSun Energy, one of the US’s largest producers of renewable fuel.

The Q microbe is actually a strain of the soil-dwelling bacterium Clostridium phytofermentans, which was isolated from forest soil collected near the Quabbin Reservoir in central Massachusetts by Thomas Warnick, a member of Leschine’s lab. The bacterium had never been described before by science and Clostridium phytofermentans was recognised in 2002 as a novel organism.

‘We were focused on anaerobes,’ said Leschine of the organisms that make a living in environments without oxygen. While going about their daily business – in this case breaking down plant litter – these anaerobes undergo fermentation. Many produce ethanol and a harmless vinegar-like substance called acetate, along with some hydrogen and carbon dioxide as waste.

What struck Leschine about C. phytofermentans was the amount of ethanol it produced. Most anaerobes make acetate as their primary product (hence the use of yeast and not bacteria for beer production), but this bacterium produced three to eight times more ethanol than acetate during fermentation.

The microbe is also unusual in its ability to consume such a wide variety of plant material. It breaks down cellulose with ease, the notoriously tough molecule that’s the primary component of plant biomass. So Leschine’s team surveyed the bacterium’s dietary preferences, feeding it everything from wood pulp waste to sugar cane bagasse, the plant matter that’s left over once sugar cane is crushed.

Pectin, starch, xylan and other plant polymers that can be difficult to digest were no problem for the microbe. ‘Q is able to break down such a wide variety of these components – it’s a real generalist,’ said Leschine.

The microbe’s enzymes are another property that makes it an ideal organism for use in large-scale production of ethanol from biomass. Usually, cellulosic ethanol production involves several steps: pre-treat the plant material mechanically or chemically to get rough biomass, treat rough biomass with enzymes that have been bought or made in a lab, add the fermenting organism, recover and purify the ethanol.

But the Q microbe’s own enzymes are more than sufficient, eliminating a costly step and consolidating production into one tank. Low estimates are that this consolidated production reduces costs by 25 percent, said Leschine.

Now that SunEthanol has secured its first round of funding, Leschine and her researchers are exploring the forms of biomass that microbe Q favours, optimising pre-treatments and fermentation conditions.