Many Disciplines Focusing On Fungus

Although the field traditionally has branched into the study of fungi species that cause disease, mycologists say their field now encompasses molecular biology, ecology, chemical-extraction techniques, and other specialties and skills not usual for the traditional mycologist. The research emanating from laboratories studying fungi is diverse, including investigations of biological control of pest plants, production of new strains of

Apr 18, 1994
Myrna Watanabe
With the advent of new molecular genetics techniques, the field of mycology--the study of fungi--has changed dramatically in the past two decades, its scope advancing rapidly. Until the 1970s, mycology was essentially an observational science. A mycologist was trained in traditional taxonomic techniques: making gross and microscopic observation of specimens, comparing them with samples in museum and research collections and illustrations in books, and classifying them by morphological characteristics.

Although the field traditionally has branched into the study of fungi species that cause disease, mycologists say their field now encompasses molecular biology, ecology, chemical-extraction techniques, and other specialties and skills not usual for the traditional mycologist. The research emanating from laboratories studying fungi is diverse, including investigations of biological control of pest plants, production of new strains of edible mushrooms, and degradation of toxic materials, as well as the search for cures for cancer and AIDS.

Fields Of Interest The object of mycologists' interest, fungi, according to Amy Rossman of the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) in Beltsville, Md., comprise these groups: lichenized fungi or lichens; mushrooms, truffles and false truffles; plant-associated fungi, including rusts, smuts and mildews; and insect- and animal-associated fungi, a category that encompasses insect and animal pathogens.

The recent advances in biochemical techniques and the surge in concern for the environment have resulted in rapid expansion in the types of scientists taking an interest in the properties of these organisms. For example, systematic mycologist Rossman, a research leader of the systematic botany and mycology laboratory at USDA-ARS, works with a team that includes a molecular systematist on classification of fungi.

Rossman explains that, in many laboratories, molecular systematists who can identify fungi from their DNA are uncomfortable attempting to identify them by using morphological characteristics.

Paul Rygiewicz of the U.S. Environmental Protection Agency's (EPA) Environmental Research Laboratory-Corvallis (ERL-C) in Oregon, a project leader in a study of mycorrhizal fungi--the network of fungal mycelia that is intimately associated with tree roots--trained as a tree physiologist and now works as a soil biologist/soil ecologist.

Meindert de Jong of the Centre for Agrobiological Research (CABO) in Wageningen, the Netherlands, is a plant pathologist. He is using a silvicidal fungus to control noxious forest weeds. And chemist Steven Aust of Utah State University in Logan has started a company that will sell licenses for technology using white rot fungus to degrade toxic materials.

Environmental Aspects Among the lines of research involving fungi is field ecology. As decomposers, fungi are essential for making soil nutrients and nutrients from dead organisms available to plants for growth.

Investigators are discovering that medical applications of fungal-derived materials may not be limited to antibiotics, like penicillin, or such antifungals as griseofulvin, which historically have been produced from fungi. Pharmaceutical companies and the National Cancer Institute (NCI) are screening compounds derived from fungi for drug activity.

EPA's Rygiewicz is studying how plants and their symbiotic mycorrhizae will adapt to changes in carbon availability. Climate change is expected to yield increased carbon dioxide concentrations in the air. According to Rygiewicz, as much as 50 percent of the carbon assimilated by trees and going below ground might pass through mycorrhizal fungi. Once processed by the mycorrhizae, the carbon becomes available for use by other organisms in the soil.

Among the questions Rygiewicz's group is asking is, if carbon availability in the atmosphere increases, will the plant become more dependent on fungi to sustain growth, or will it increase root growth? What effect will a change in reliance on mycorrhizae have on the other portions of the soil food web?

The New York Botanical Garden's Roy Halling, in cooperation with colleagues at Chicago's Field Museum of Natural History, is surveying mushrooms and other fungi in Costa Rica's relatively young (approximately 350,000 years old) oak forest. The concern is that if the oak forest were destroyed, the nutrients that are recycled through the system by the fungi would leach out and be lost. When you destroy the forest, Halling says, "not only do you wipe out the nice charismatic macrofauna; you destroy a heck of a lot more."

Utah State's Aust got the idea to start his company, Intech One-Eighty Corp., when, at Michigan State University, a graduate student approached him with a fungus that could degrade toxic material. Aust recognized the enzymes that caused the white rot fungus, Phanerochaete chrysosporium, to degrade lignin in wood. He has been working with the fungus ever since. In a recent paper (D.P. Barr, S.D. Aust, Environmental Science and Technology, 28:78A-87A, 1994) Aust explained that because this degradation is extracellular, the fungus also is capable of degrading many pollutants, including cyanides; polycyclic aromatics, such as pyrene and anthracene; pesticides, such as DDT and chlordane; and munitions, such as TNT.

CABO's de Jong expects that "biological control of weeds, pathogenic fungi in crops, and harmful insects may have a bright future." He now is studying use of the naturally occurring fungus Chondrostereum purpureum, a common wood saprophyte and sometimes parasite, to control resprouting of poplar stumps in poplar plantings in a newly reclaimed polder--an area that had been under water--in the Netherlands. Prior to this, de Jong used this fungus to control the North American black cherry, Prunus serotina, an introduced weed that competes with naturally occurring species.

Magic Mushrooms Systematic mycologists like Richard Kerrigan, director of research for Sylvan Research, a Cabot, Pa.-based mushroom spawn supplier, have also gained from molecular biological advances. Kerrigan has been studying wild species of Agaricus, the genus that contains the cultivated button mushroom, A. bisporus.

Kerrigan explains that A. bisporus "has [predominantly] a closed sexual cycle, in which only a single parent is needed to give rise to each new generation of offspring." This makes crossbreeding very difficult, he says. Along with French colleagues, Kerrigan described a wild variety of this species that can be crossbred with the cultivated variety (P. Callac, et al., Mycologia, 85:835-51, 1993). This may lead to more genetic variability within cultivated mushrooms.

Several amateur mycologists tout mushrooms as curing many ills, including hypertension, cancer, and AIDS, although this is not a burgeoning area of research at present.

One of the most visible proponents of the medicinal use of mushrooms is Paul Stamets, an entrepreneur who established a mushroom company, Fungi Perfecti, in Olympia, Wash. Much of the research Stamets relies on regarding health claims of mushrooms was carried out in China and Japan.

David Newman, a chemist with the Natural Products Branch of NCI, screens natural compounds, including many varieties of fungi, for activity against HIV and cancer. He says, "Although a large number of aqueous extracts of fungi show initial activity in the HIV screen as it is run at NCI-FCRDC [Frederick Cancer Research and Development Center], the activity almost in all cases is due to the presence of soluble polysaccharides." He points out that these high-molecular-weight polysaccharides "are not useful as drug entities." One reason for this, he explains, is that there is no way to deliver such large molecules into the body. Many of the molecules discovered in Chinese and Japanese research, he says, are high-molecular- weight polysaccharides. NCI is, however, supporting clinical trials of a ketone isolated from Fusarium javanicum, a fungus that grows on yams. Phase I clinical trials in patients with nonsmall-cell carcinoma of the lung are being carried out at the NCI-Naval Oncology Branch, while phase II clinical trials in patients with hepatocellular carcinoma have been approved and are expected to begin soon at Johns Hopkins Hospital in Baltimore. Rygiewicz and de Jong see increasing environmental involvement by mycologists in the future. Aust, in describing detoxification of environmental contaminants, says, "One of the interests in this field is that it has potential in the market."

Research in the field is supported in many ways, but not extravagantly. The National Science Foundation funds taxonomic research in mycology. Investigators such as Rossman and Rygiewicz are financed by their agencies. Aust's work has been funded by the National Institutes of Health, EPA, and corporate sources.

Halling is encouraged that NSF will begin a program for training taxonomists, particularly in fields in which they are underrepresented, such as mycology. He also is glad that the National Biological Survey (NBS), a new unit of the Department of the Interior, has made fungi a high priority. "If we really want to get a handle on the old-growth forests, we better start looking at what's going on underground with mycorrhizal fungi," according to a statement by Gene Hester, acting NBS director.

Thus, although the field has widened, mycologists are still wondering where the jobs will be and how research will be supported. "The future is bright," says Halling, "but at present, it's kind of bleak."

Myrna E. Watanabe is a biotechnology consultant based in Yonkers, N.Y.