GMO methanogen for glycerin digestion

By Erin Voegele | November 17, 2010
Posted Dec. 15, 2010

A researcher at the University of Arkansas has created the first methane-producing microorganism that can metabolize complex carbon structures. The project could lead to the development of a microbial process to recycle waste products, such as glycerin from biodiesel plants, into a renewable form of natural gas.

According to David Lessner, an assistant professor of biological sciences who is leading the research, the project focused on methanogens, which are methane-producing anaerobic microorganisms. "These are microorganism that grow only in anaerobic-or oxygen free-environments, but they are found in very diverse environments," he said. "They grow by producing methane gas as an end product."

One of the primary limitations of methanogens in methane production is that they are only able to digest a very limited range of substrates, Lessner said. To produce methane in nature, these mircoorganims must work in a consortium with other microorganisms that break down complex carbon sources into compounds they can consume. The basic premise of the study, Lessner continues, was to provide a methanogen microorganism with the genetic ability to break down more complex compounds and produce methane.

The research conducted by Lessner and his colleagues focused on a strain of methanogen known as Methanosarcina acetivorans. According to Lessner, this particular strain was used because it can naturally consume more substrates or chemicals than most other methanogens. "But, it's still limited," he continued. "We we thought it would be a good platform to begin adding to the catabolic capabilities of the organisms, so we used that as our starting microorganism."

The project involved isolating a gene from a strain of bacteria that is able to consume a wide range of substrates, but cannot produce methane. The gene was transferred from the bacteria to the methanogen. "We were able to show that the methanogen could recognize that gene and make the enzyme, and then that allowed the methanogen to consume more complex esters and convert them into methane gas, where the original parent strain is unable to do so," Lessner said.

While Lessner noted it is not feasible to genetically modify methanogens to the extent that they could be used to convert complex mixes of biomass feedstocks into renewable methane, he notes that it might make sense to specifically modify the microorganisms to convert specific biorefining waste streams into methane, which could then be used as renewable natural gas. One specific example of this type of application is the conversion of glycerin coproduced at biodiesel plants.

The next step in the research will involve further modifying the methanogen to digest more slightly more complex substrates. In addition to investigating the potential for renewable natural gas production, Lessner said the research his team is conducting might provide technology developers with new insight into the use of methanogens in industrial processes. While the use of bacteria in industrial processes has been widely studied and is well understood, there has been much less investigation regarding the use of methanogens in industrial processes.
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