Researchers use bacterium to convert cellulose into n-butanol

By Bryan Sims | September 01, 2011

A team of researchers at Tulane University have discovered a unique bacterial strain of clostridia, coined TU-103, that has the ability to convert cellulosic materials into biobased normal butyl alcohol, or n-butanol.

Associate professor of cell and molecular biology David Mullin, who supervised the research, said he and his team first identified TU-103 in animal waste. It was then cultivated and incorporated for use on cellulose to produce n-butanol. While old, discarded newspapers grabbed most of the headlines as a source of cellulosic material, Mullin said that the research also used cotton, filter and hard papers. Mullins said they produced quantities of n-butanol in the 200-mililiter range and plan to scale up to a 10-liter bioreactor, once ideal conditions are met.

“The reason why used newspapers was because they are easy to get a hold of and play with,” Mullins said.

While some procedures are to pretreat cellulosic material with an acid or base before it goes through fermentation, Mullin said he was able to bypass the pretreatment step. For the process, Mullin and his team took the cellulosic material, soaked it in water and then put it into a waring blender to break it up into small pieces, which were then mixed with broth and put in an autoclave for sterilization. When it cooled, they inoculated the material with TU-103 bacterial strain. In addition to n-butanol, Mullin said the process also yielded nominal amounts of acetone, butyric acid and acetic acid.

To make n-butanol, the researchers used a specific type of butanol-producing clostridial strain called Clostridium acetobutylicum. While it’s one that has been used to make butanol for a long time, Mullin pointed out that it’s the only one to his knowledge that that can feed on cellulose and produce butanol in the presence of oxygen, which typically kills butanol-producing bacteria.

“All of the clostridia that make butanol are very strict anaerobes,” Mullin explained. “We can streak it on an agar plate and it will form nice, large colonies in air. The fact that you can do that with it makes it much easier to handle, because with clostridia that are strict anaerobes, you really have to take special precautions to make sure that no oxygen gets into the culture.”

Mullin said his team has finished putting together the nucleotide sequence for the genome of the TU-103 bacterium, which will give the team a more manageable biochemical route with use of the genome compared to utilizing recombinant DNA technology.

“It just makes it more straight-forward as opposed to starting with an organism that’s in a black box,” Mullin said.

A patent has been filed by the university on the process. Tulane University is one of five universities sponsored by the U.S. DOE involved in the Clean Power and Energy Research Consortium. Its focus is aimed at addressing critical scientific issues in power and energy generation.