Tom Volk's Fungus of the Month for May 1997

This month's fungus is Phanerochaete chrysosporium, a crust fungus important in biotechnology.

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Phanerochaete chrysosporium growing on woodIf you're only familiar with fungi in the form of mushrooms, then this month's fungus may surprise you. Phanerochaete chrysosporium is one of those resupinate, or crust fungi, that decays wood. There are lots of these resupinate fungi and they are responsible for a good deal of the wood decay in logs that are lying on the ground in nature. These fungi never form a mushroom for reproduction, but form effused, very flat, fruiting bodies that appear as no more than a crust on the underside of a log. You're probably squinting your eyes right now to try and see the fruiting body in the picture--- It's kind of a white fuzz in the middle of the picture. Until you start to examine these more closely they all look the same. Microscopically, however, they are quite interesting and even beautiful.

Phanerochaete chrysosporium was described by Hal Burdsall , my former boss at the Forest Products Lab in Madison, in 1974, as a fungus decaying wood chips (Burdsall, Harold H., Jr, and W. Eslyn. 1974. A new Phanerochaete with a Chrysosporium imperfect state. Mycotaxon 1:124). The fungus has been isolated fewer than 50 times from "the wild," but we don't really know how common it may be, as it can be easily overlooked because of its thin cobwebby appearance. It is a member of the Basidiomycota, which means it bears its meiotic spores externally on a structure called a basidium. On the surface, it is a pretty inconsequential-looking fungus.

A=White rot B=Brown rot

However it is the lignin-degrading enzyme system of this fungus that makes it very special. In order to understand this system, you must know that wood consists primarily of cellulose, which is white, and lignin, which is brown. Phanerochaete (usually pronounced fan-er-oh-KEE-tee) species cause a white rot of wood. That is, the fungus decays the lignin and leaves the cellulose behind (left picture). There are also fungi that cause a brown rot, digesting the cellulose and leaving the lignin behind (right picture). There are many kinds of fungi that cause a white rot, but Phanerochaete chrysosporium has several features that might make it very useful. First of all, unlike some white rotters, it leave the cellulose of the wood virtually untouched. Secondly it has a very high optimum temperature (about 40 C), which means it can grow on wood chips in compost piles, which attain a very high temperature. These characteristics point to some possible roles in biotechnology.

wood chip pile


One of the biggest energy expenditures in paper making comes from removal of the brown lignin from the wood so that the white cellulose is all that's left to make paper. What if paper companies could use the enzymes of a white rot fungus to remove the lignin? This could result in a savings in both energy and time and avoid pollutive wastes being dumped out of the mills. The ideal fungus for this endeavor would be fast growing, able to tolerate high temperatures, and would leave the cellulose virtually untouched. This ideal fungus would have the exact characteristics of Phanerochaete chrysosporium.

fungi degrade toxic waste


Some of the lignin-degrading enzymes of Phanerochaete chrysosporium will also degrade toxic wastes, such as PCB's and PCP's. This is not too surprising, because those substances have chemical bonds very similar to those found in lignin. The fungus works very well on the laboratory bench, but, as with many industrial bioprocesses there are problems with scaling up the process.

As of very recently, Phanerochaete chrysosporium is the first wood-decay basidiomycete to have its genome sequenced. This genome sequence will certainly help with manipulations of Phanerochaete in future biotechnological applications. You can read more about the genome sequencing in the June 2004 issue of "Nature Biotechnology." The first photo of Phanerochaete chrysosporiumon this page appeared in an article announcing the sequencing of the genome.

Phanerochaete crassaThere are about 46 other species of Phanerochaete, as found in Hal Burdsall's 1985 monograph of that genus. "A contribution to the taxonomy of the genus Phanerochaete " Mycologia Memoirs. Phanerochaete species generally have cordons, groups of hyphae on the edges of the fruiting body and they all generally have simple septate hyphae. If clamps are present there are usually multiple clamps at the septa, as shown in the background of this page. Not all of them are cobwebby in appearance. some of them are even quite beautiful including the purple Phanerochaete crassa.

Phanerochaete chrysorhizonYou might also find the spectacular Phanerochaete chrysorhizon, named for its orange-yellow rhizomorph-like cordons emanating from the toothed fruiting body. Phanerochaete chrysorhizon is a rather common fungus, but often only the cordons can be found, with the fruiting bodies appearing later in the year. It often covers the whole underside of a down log.

I hope this page has encouraged you to turn over a few logs while you're out in the woods. You're almost certain to find some sort of resupinate crust fungus on the underside of the log. There are several hundred different species in more than 100 genera. If you have a microscope, I would suggest you take the fungus home and examine it. You might be surprised what you find! An added advantage of collecting resupinate fungi is that you are almost never "skunked" on your fungus foray-- the undersides of logs remain moist long after everything else has dried out.

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This page was revised June 2, 2004.

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