Genetic Manipulation of Lignin Synthesis in Switchgrass Reduces Recalcitrance and Improves Ethanol Production

Scientists from the Samuel Roberts Noble Foundation, Oak Ridge National Laboratory, and Georgia Institute of Technology (United States) report their attempts to produce low-lignin switchgrass, by genetic manipulation of its lignin biosynthetic pathway. Switchgrass is a high-yielding perennial prairie grass, with low agronomic inputs, and is considered a potential (lignocellulosic) feedstock for bioethanol production in the United States.

Recalcitrance, on the other hand, is the property of (lignocellulosic) biomass to resist pretreatment (usually a severe thermochemical process applied to biomass, to remove lignin, and to modify the structure of cellulose/hemi-cellulose fractions for easier processing to ethanol). The lignin content in the biomass is considered to be a major cause of recalcitrance. Thus, attempts have been made to use molecular biology techniques to produce low-lignin bioenergy crops, with the objective of reducing biomass recalcitrance and to reduce pretreatment cost.

The scientists reduced the lignin content in switchgrass by "down-regulation of the switchgrass caffeic acid O-methyltransferase gene". The genetically modified switchgrass required less severe preatreatment, required a lower enzyme dose for the subsequent saccharification process (by 300 percent to 400 percent), and increased ethanol yields by about 38 percent. They were able to show that the "apparent reduction in the recalcitrance of transgenic switchgrass has the potential to lower processing costs for biomass fermentation-derived fuels significantly" and that "modified transgenic switchgrass lines should yield significantly more fermentation chemicals per hectare". The study is published in the (United States) Proceedings of the National Academy of Sciences (PNAS) (URL above).