PR rainforest holds hope for biofuels
Scientists have long seen promise in the wild biodiversity of the world’s rainforest in the search for cures to diseases and new fuel sources.
Now, researchers from the U.S.-based Joint BioEnergy Institute at the Lawrence Berkeley National Laboratory have found a microbe living in the soil of Puerto Rico’s El Yunque National Forest that can dissolve lignin, that tough woody polymer in plant cell walls that proves to be such an obstacle in cellulosic biofuel production.
Researchers have harvested the soil microbes during expeditions into El Yunque, the only tropical rainforest in the U.S. national forest system. The misty mountainous expanse was also designated as the Luquillo Experimental Forest nearly six decades ago to recognize the growing importance of research.
Lignin, a complex polymer of aromatic alcohols, is an integral part of the secondary cell walls of plants and some algae. By its nature, lignin inhibits access to cellulose, reducing accessibility of plant sugars for biofuel production. The lignin in plant cell walls that helps protect energy-storing sugars must be degraded for cost-effective production of advanced biofuels.
Researchers at the Joint BioEnergy Institute (JBEI) have characterized the enzymatic activity of a rainforest microbe that breaks down lignin essentially by breathing it.
“We detected significant lignin degradation over time by absorbance, suggesting that enzymes in E. lignolyticus could be used to deconstruct lignin and improve biofuels production,” said Blake Simmons, a chemical engineer who heads JBEI’s Deconstruction Division. “Our results also demonstrate the value of a multi-omics approach for providing insight into the natural processes of bacterial lignin decomposition.”
Not only does lignin inhibit access to cellulose, the by-products of lignin degradation can also be toxic to microbes employed to ferment sugars into fuels. This makes finding microbes that can tolerate a lignin environment a priority for biofuels research.
Tropical rainforests harbor anaerobic microbes that actually utilize lignin as their sole source of carbon. Kristen DeAngelis, a microbial ecologist formerly of JBEI and now with the University of Massachusetts, has led expeditions to the Luquillo Experimental Forest.
“Tropical soil microbes are responsible for the nearly complete decomposition of leaf plant litter in as little as eighteen months,” she said. “The fast growth, high efficiency and specificity of enzymes employed in the anaerobic litter deconstruction carried out by these tropical soil bacteria make them useful templates for improving biofuel production.”
A study showed that E. lignolyticus SCF1 is able to degrade lignin via both assimilatory and dissimilatory pathways, the first soil bacterium to demonstrate this dual capability.
“Our next step is to look at what kind of chemical bonds are preferred by these two different pathways of reduction,” DeAngelis said.
This would help researchers to better develop ways to use the bacteria and its enzymes in the biofuel process.