The marine invertebrates known as gribble have plagued seafarers for centuries. Scientists, however, hope to turn an enemy into an ally, using gribble’s unusual capacity to break down the lignin in wood to create better biofuels.
Vascular plants use lignin in their cell walls for strength, particularly in wood and bark. Lignin also impedes the process of breaking wood down to get at the sugars within. Nevertheless, some animals, fungi, and bacteria have found ways to consume lignin. Replicating their success could lead to transport fuels with no net carbon emissions.
"Gribble are the only animal known to have a sterile digestive system,” said Professor Simon McQueen-Mason of the University of York in a statement. “This makes their method for wood digestion easier to study than that of other wood-consuming creatures such as termites, which rely on thousands of gut microbes to do the digestion for them."
McQueen-Mason has found part of gribbles' success can be attributed to proteins called hemocyanins. Hemocyanins perform a similar role in crustaceans to hemoglobin in vertebrates, transporting oxygen to the organs that need it. Where hemoglobin binds oxygen to iron, hemocyanin uses paired copper atoms, making the blood of the animals that possess them bright blue.
Gribble have repurposed hemocyanin to sever lignin's chemical bonds in wood washed into the oceans. They then attack the weakened material with enzymes similar to those used by fungi. It's made gribble a menace to those who sail the seas in wooden boats or depend on wooden jetties. For McQueen-Mason and co-authors of a paper in Nature Communications, however, the capacity is one to copy.
The researchers treated wood with hemocyanin for 20 minutes, and increased sugar release by 50-300 percent, which in turn could greatly cut the cost of biofuels produced from lignin-rich plant materials. These sugars can then be fermented into transport fuels, with the carbon dioxide released in their burning offset by the what the plants capture from the atmosphere as they grow.
Biofuels have been touted as the solution to the energy crisis and climate change, but have often ended up doing more harm than good. It's easy enough to turn existing crops like corn and sugar cane into ethanol for fuel, but doing so drives food prices higher, contributing to hunger and food riots.
According to the researchers, woody plant biomass is the most abundant renewable carbon resource on the planet, and doesn't come into conflict with global food security. However, even some alternative biofuels that aren't based on things we can eat compete with food crops or wildlife habitat for space. There's a danger wood-to-fuel technology will become another excuse to chop down forests. However, by opening up a wider range of plants that can be made into transport fuels, it could also increase the prospects of sourcing materials from degraded lands that can be used for little else.