Among alternative renewable fuels currently being researched for efficacy, algae has sparked considerable interest. Some of its potential advantages over other biofuels include its ability to be grown in areas unsuitable for either growing typical vegetable food crops such as corn or for raising animals for meat. Switchgrass and wood are both renewable and can be grown on land unsuitable for crops or grazing, but both contain lignin, a polymer made by plants to strengthen their cell walls. The presence of lignin makes it much harder to extract the sugars needed to make alcohol from these plant sources. Algae do not contain lignin but the effort to extract sugars is hampered by the fact that much of their sugar is polymerized to form a complex chemical called alginate which cannot be easily converted into ethanol by current industrial microbes (yeast or bacteria).
This then becomes the bioengineering challenge. Can we genetically alter yeast or bacteria sufficiently to give them the ability to digest alginate and efficiently covert the resulting sugars into ethanol? To date, the story is a fascinating example of our current state of molecular biology and our ability to alter the chemistry and genetics of these micro-organisms without inhibiting their extraordinary ability to multiply.
Researchers in Berkeley, California, began with E. coli, the common (usually harmless) bacteria of our intestinal tract. They extracted a gene from a marine bacterium that makes an enzyme that breaks alginate down into small fragments and put that gene into E.coli. From another micro-organism they obtained a gene that enabled the E. coli to excrete this enzyme into the culture medium, and then another gene was introduced to allow the bacteria to take up the resulting small fragments of alginate. Finally, from a fourth bacterium they had isolated from fermented cane juice, they obtained a gene that, when introduced into their E. coli, turned the alginate fragments into ethanol with high efficiency.
Questions and suggestions from readers are welcomed and will be responded to in future editions of this column. Contact me at firstname.lastname@example.org.