Microbial Duo Turns Cellulose Into Fuel

Fuels derived from biological processing of cellulose could serve as environmentally friendly gasoline replacements. But organisms that break the complex plant matter into sugars and convert them to fuels on a commercial scale have proved elusive. Now, Jeremy J. Minty of the University of Michigan, Ann Arbor, and coworkers report using not one but two microbes to make a cellulosic biofuel from inedible plant matter (Proc. Natl. Acad. Sci. USA 2013, DOI: 10.1073/pnas.1218447110). The fungus Trichoderma reesei hydrolyzes cellulose to sugars, and genetically engineered Escherichia coli in the same reaction vessel converts the sugars to isobutyl alcohol. When burned, the alcohol produces 82% as much energy per gallon as gasoline and slightly more than ethanol. Microbes given corn roughage that was pretreated to improve its microbial digestibility generated a product mixture containing isobutyl alcohol in high concentration and in yields reaching 62% of the theoretical maximum. Both organisms feed on the sugars, and competition can ensue. If one microbe dominates, conversion to isobutyl alcohol will cease. The researchers have found conditions, however, where both T. reesei and E. coli survive and convert the cellulose to isobutyl alcohol as desired. Now they aim to optimize the microbial system and assess its larger-scale performance. The concept could be adapted to make commodity chemicals, the team notes.