How to Find New Enzymes for Making Cellulosic Ethanol

by Emil Morhardt

Nonedible agricultural waste plant material is the most abundant ready source of biomass for making ethanol. But this “cellulosic” ethanol is expensive because breaking down the lignocellulose in plant waste so it can be fermented to ethanol requires either large amounts of energy, or specialized enzymes that are costly to manufacture. Furthermore, the enzymes discovered so far are not as resistant as they might be to the high temperature and high solids (low water) environments that work best for industrial processing.

One way to discover new candidate enzymes is to look for them where they are being produced naturally in an abundant source of agricultural waste; in this case, composting rice straw greenwaste. Genetic engineering technology makes it efficient to look not for the enzymes (proteins) directly, but for the messenger RNA that codes for them—the mRNA that is being actively transcribed from the various microbial genomes present. To distinguish the appropriate genes, a comparison can be made between the RNA products from room temperature (mesophilic) and heated (thermophilic) cultures degrading rice straw. The actual technique is to collect the mRNA, use it to create its complimentary DNA, then sequence the cDNA, looking for genes that code for protein families likely to be involved in degrading lignocellulose. Continue reading

Cellulosic Ethanol Technically Comes of Age

by Emil Morhardt

Making liquid fuel out of crop waste is, in principal, an extremely good idea. But the ethyl alcohol (ethanol) we add to gasoline—and also drink in vodka, wine and beer—has been made out of edible fruits and grains. Corn ethanol, the main gasoline substitute is made out of the corn kernels which otherwise might become corn meal or tortillas, cutting into the food supply and encouraging conversion of more land into cropland. There have been many studies on the effect of this land conversion on atmospheric CO2 levels, and it appears that it will often be a decade or more before the CO2 released from land conversion will be offset by the substitution of ethanol for fossil fuels. Continue reading