Pumping Out the Biofuel

By Daniela Sciaky, Ph.D.

A $50,000 ConocoPhillips Energy Prize was recently awarded to the research team headed by Gregory Stephanopoulos of the Massachusetts Institute of Technology for engineering of a microbe that converts carbohydrates into lipids. The significance of this award is that the patent-pending technology has resulted in the creation of a heterotrophic microbe that, according to Stephanopoulos, has remarkable yields. These yields, which are reported to be close to the theoretical maximum, will help to reduce the cost of producing oil-based biofuels such as biodiesel.

The prize from ConocoPhillips is to be used by the MIT team to explore the use of hydrogen and carbon dioxide as feedstocks for the microbe. One of the schemes proposed by the team sends the carbon dioxide produced by the aerobic (organisms that grow in the presence of oxygen) heterotrophic oil-producing microbe from fermentation to a separate fermentor for use by anaerobic bacteria in the presence of hydrogen, resulting in the production of ethanol. This scheme converts carbohydrate and hydrogen to both oil and ethanol.

In another scheme anaerobic bacteria or bacteria that grow in the absence of oxygen are used to fix carbon dioxide with hydrogen to produce the feedstock for use by the aerobic heterotrophic oil-producing microbe. This scheme converts hydrogen to oil for production of high-density biofuels. The technology proposed in these schemes has been proven in different contexts to varying degrees. Existing facilities can be used to test the scalability of the technology.

Are there any companies proposing or commercializing a similar approach? As discussed in a previous post “Algae, the Dark Side of Solazyme’s Success”, Solazyme has successfully used the heterotrophic concept to produce algal-based renewable naval distillate fuel for the US Navy. The company continues to explore the use of cheap sources of fixed carbon such as conversion of biomass to sugars for fermentation by heterotrophic microorganisms. Qteros has developed the Q Microbe also known as Clostridium phytofermentans, capable of digesting a variety of cellulosic feedstocks as a source of fermentable sugars. The organism can then ferment these sugars to produce ethanol. Qteros reports that it has significantly improved the yield and titre of ethanol produced by optimizing the microbe’s metabolism.

The key to success is that the heterotrophic microbe developed by the MIT team has yields close to theoretical maximum.  Historically, production of oil from oleaginous microorganisms, organisms whose lipid content is more than 20% of their biomass, has been prohibitively expensive, ranging from $1000 to $2400 per ton. High costs result from the need to supply microorganisms with a carbon source and the slow cell growth rate during fermentation resulting in high lipid accumulation with very few cells. Only when these costs become competitive with production of biofuels from oilseeds or sugar/starch-based feedstocks will production of biofuels from heterotrophic microorganisms gain favor.