Fuel ethanol in gasoline pumps around the world has been largely produced through biological fermentation from corn starch and plant sugars. Producing cellulosic ethanol from non-food feedstock such as agricultural and forest residues has encountered in decades serious challenges of bio-toxicity to fermentation microbes due to the presence of toxic chemicals. The processes of biomass pretreatment that are necessary to generate cellulosic sugars for ethanol production also inevitably generate toxic chemicals as byproducts. These chemicals significantly reduce the rates of yeast metabolism and the final ethanol titers in the fermentation step. Some detoxification techniques, including water washing, physical, chemical, and biological methods, increase capital investment and operational costs, and cause the loss of sugars.
A research team in the DNL 602 group, led by Professor Z. Conrad Zhang at the Dalian National Laboratory for Clean Energy, Dalian Institute of Chemical Physics, has developed an in-situ chemical detoxification process by adding polyethyleneglycol (PEG) that protects the yeast cells from harm by the toxic chemicals. In the presence of PEGs, the fermentation process becomes smooth with high ethanol yield by simply using a starch-base industrial S. cerevisiae. This work is now online published in the journal of Scientific Reports（doi:10.1038/srep20361）
The PEG exo-protected yeast cells displayed remarkably improved ethanol productivity from a crudely pretreated lignocellulose sources such as poplar and corn stover. By adding PEGs, the starch-base industrial S. cerevisiae becomes directly applicable for the production of cellulosic ethanol without the need to use genetically modified microorganisms. This discovery allows simplified cellulosic ethanol production process with reduced capital investment. The research team is currently working on a scale up process for cellulosic ethanol production from several lignocellulosic feedstocks collected from the field.
Armored yeast cells produce cellulosic ethanol unharmed by toxic chemicals(Photo by LIU Xiumei)
“The PEG can be reused. The detoxification fermentation process largely improves the economics of cellulosic ethanol production.” Said Dr. Xiumei Liu, the lead author of the paper. (ext/Photo by LIU Xiumei）