In “The Enigma Remains” (Biologic Institute blog, July 6, 2012), Ann Gauger
responds to recent critics of a paper on the curious fact that life forms cannot usually digest lignin:
Some people who have read the paper, or at least the introductory blog post, have felt compelled to respond by digging up examples of lignin degradation from the literature.
There are a few things to note in response. First, Dr. Matti Leisola, the primary author of the paper, has worked on this subject for decades, and is widely respected by his peers. He did not “overlook” any references concerning lignin degradation. This should have been clear to anyone reading the paper, as the following quote shows:
The degradation of lignin by white-rot fungi has some special and even strange features. Firstly, lignin is not degraded during fungal growth but only after nutrient depletion triggers secondary metabolism. This is strange since secondary metabolism is usually connected to biosynthetic reactions rather than degradative processes. Secondly, despite the fact that complete oxidation of lignin is highly exothermic, fungal degradation of lignin actually needs an energy source. It has been postulated that lignin degradation is too slow to serve as a source of metabolic energy. Hatakka and Hammel ponder the possibility that “if lignin fragments were metabolized intracellularly, at least some energy and carbon should be gained from lignin for the fungus, and the fungus should be able to grow on lignin”. This is questionable since it is apparent that the faster lignin is degraded the more energy is needed. Under optimal aerobic culture conditions, one gram of fungal mycelia degrades one gram lignin in about 48 hours consuming one gram of glucose in the process (as an energy source). Once glucose is depleted, lignin degradation ceases completely. And finally, fungi use the same kinds of enzymes (peroxidases and laccases) to initiate lignin degradation that plants use to make lignin. We call these curious features the lignin enigma.
In short, fungi can break down lignin but need glucose as an energy source to do so.
On-line critics cite several papers to argue that lignin can be used as a sole carbon source. …
Hey, Gauger, they’d cite a serial fraudster as their star witness if they thought he protected Darwin.
UD News can’t resist noting: If life forms could just eat wood, there would never be a canoe afloat on the Ganaraska (“Float yer fanny down the Ganny”), let alone a deck to watch the waterborne parade from.
See also: Design of life: Why can’t most life forms digest wood?