Fungi, plastics and sustainability
Oliver Klaffke
Researchers at the University of Basel are investigating how fungi and bacteria decompose wood. This basic research is facilitating the production of new materials – and might also provide clues about processes that maintain human health.
At some point during the Carboniferous Period, nature suddenly found itself facing a garbage problem of mammoth proportions. Trees grew very tall and, when they died, left behind a huge amount of wood that could not be broken down by the organisms that were alive at the time. The blame lay with lignin, a chaotic mixture of structurally similar molecules that stabilizes wood by filling in the gaps in its cellulose scaffold. “It took quite a while for mechanisms to develop that could break down lignin,” says Florian Seebeck, a professor of chemistry at the University of Basel.
Seebeck’s work involves looking at how fungi break down lignin. He is especially interested in finding out how fungi survive the decomposition process unscathed, as the slow shredding of the molecular chains produces chemical reactions that are aggressive to all forms of life. “The fungi are under oxidative stress during the splitting,” says Seebeck. This stress occurs when free radicals (molecules with a strong tendency to bind to other substances) are released, attach themselves to the tissue of the fungus and damage it.
A source of new biomaterials
Lignin is being discussed as an alternative to oil. It could, for instance, replace oil in the manufacture of plastics and thereby play a key role in the wood technology of the future. For that to happen, however, lignin has to be broken down into small molecular units. This means that everything scientists can find out about the chemistry and biological decomposition of lignin will help bring us closer to a sustainable industrial use of wood.
“Fungi and bacteria have developed a form of protection that allows them to survive the oxidative stress,” says Seebeck. The key is a molecule known as ergothioneine, which puts free radicals out of commission. Last year, Seebeck and his team worked out how ergothioneine is synthesized. The literature contained findings on a precursor of the substance, but the mechanism that turned the precursor into a functional molecule was unclear. “We found an enzyme that synthesizes it,” says Seebeck, who gave the enzyme the prosaic name EgtB.
Ergothioneine does not just occur naturally in bacteria and fungi; the protective substance has been found in almost every organism. “Its presence in humans was established over 100 years ago, but no one has paid it much attention,” says Seebeck. The reason for this is simple: no diseases are caused by a deficiency of ergothioneine. It seems that the body always has sufficient supplies because it does not break down much, in contrast to vitamin C, for instance, which quickly degrades and a deficiency will lead to scurvy.
“This is why people quickly recognized that vitamin C was important for human health,” explains Seebeck, “and why they overlooked ergothioneine.” Yet the role that it plays in the human body could be as important as the one it plays in the bacteria and fungi that break down lignin. “Oxidative stress occurs everywhere in nature,” says Seebeck. It would not be surprising if the successful molecule also had an antioxidant effect in humans.