Insects' gut microbes hint at biofuel breakthrough

Researchers compared gut microbes from grasshoppers, termites and caterpillars

Flickr/ Ismah Mansourah

[BEIJING] Deep inside insects' guts may lie the key to one of the biofuel industry's great challenges: how to cost-effectively turn tough plant waste into profit-making fuel.

About 50 million tonnes of lignin are produced every year worldwide, mostly as waste after the sugar, or cellulose, in a plant has been converted into ethanol.

Finding a way to process this tough molecule could boost biofuel production and cut the greenhouse gases that are emitted when it is burned as waste.

Insects harbour natural catalysts that could be exploited to convert plant material into biofuels more efficiently, report scientists in a paper in PLoS Genetics this month (10 January). Herbivorous insects often rely on microbes in their guts using these molecules to digest plant materials such as cellulose and lignin.

By comparing the genomes of gut microbes from grasshoppers, termites and cutworm caterpillars, the scientists found that the diversity of gut microbes present and their ability to break down plant materials are linked to what the insects eat. These findings could be used to guide future searches for enzymes for use in the biofuel industry, they say.

"The study reveals that insect gut microbes evolve to adapt to different food types," says Joshua Yuan, assistant professor in systems biology and bioenergy at Texas A&M University, United States, and the corresponding author of the report.

In addition, the researchers found that grasshoppers might be a good target for biocatalyst discovery because their guts harbour enzymes that can break down cellulose.

The new enzymes could be used to reverse design biorefineries for more efficient biomass degradation, according to Yuan.

Yuan's laboratory has received a US$2.4 million grant from the US Department of Energy to try to use enzymes found in termite guts and microbes to design a way of turning lignin into biofuel.

"You can make anything but money out of lignin," Yuan says. Yet, so far there have been no good commercial uses for lignin waste, he says.

Neal Stewart, a professor of plant sciences at the University of Tennessee, United States, says that insects and their gut microbes have been widely ignored as sources of enzymes to break down materials such as cellulose and lignin.

"Yuan's idea to cast a wide net to take advantage of biodiversity is a smart one," he tells SciDev.Net.

Li Shi-Zhong, executive director of the MOST-USDA Joint Research Center for Biofuels from Tsinghua University, China, says: "Biofuels are the only practical and competitive large-scale substitute to petroleum."

"People have spent dozens of years and hundreds of millions of dollars investigating enzymes for cellulosic biofuel production," he says. "Unfortunately, the traditional technology can't overcome the economic bottleneck."

Li adds that Yuan's team is seeking a cost-effective way to produce fuel from biomass "without any impact on food and feed security".

Link to full paper