Fungi have great ecological impact. They are very important as decomposers and symbionts. Fungi, along with saprobic bacteria, play vital role in the recycling of inorganic nutrients in the ecosystem. Without their activity all the essential nutrients would soon become locked up in the mounds of dead animals, plants, would be unavailable for use by organisms, and life would cease. Mycorrhizal fungi improve the growth of plants with which they are associated. 95% of all kinds of vascular plants have this association.
Lichens growing on rocks break them, setting stage for other organisms during the course of ecological succession. Lichens are very good bioindicators of air quality as they are very sensitive to pollution. Some fungi are also used for bioremediation ( degrading/ removing environmental poisons/ pollutants by organisms).
Fungi cause economic gains as well as losses.
Economic gains due to fungi
- Certain fungi are edible. About 200 species of mushrooms (e.g. Agaricus sp), morels (e.g. Morchella esculenta), truffles (underground fruiting bodies some
Fig. 8.13 Edible fungi (a) A common morel (morchella esculenta). (b) the truffles (tuber species) are underground fruiting bodies that people find with the help of trained dogs or pigs.
Ascomycetes, e.g. tuber sp) are common edible fungi. Beware of poisonous mushrooms called the toadstools, such as death cap/death angel (amanita) and jack-O, latern mushroom (fig. 8.14).
Fig. 8.14 a: poisonous mushroom Jack-O’ lantern (omphalotus olearius) whose gills glow in the dark. B: amanita, another common poisonous mushroom.
Reindeer moss (a lichen, not a moss) is used as food for reindeers and some other large animals in arctic/subarctic/boreal regions.
- Certain fungi are used in food industry. Because of their fermenting ability, yeasts (saccharomyces cerevisiae) are used in the production of bread and liquor. Penicillium species are used for giving flavor, aroma and characteristic colour to some cheese. Some species of Aspergillus are used for fermenting/producing soya sauce and soya paste from soya bean. Citric acid is also obtained from some Aspergillus species.
- Some fungi are source of antibiotics and some other drugs. Penicillin, first antibiotic to be ever discovered (by A. Fleming-1928) is obtained from penicillium notatum. Lovastatin is used fro lowering blood cholesterol; cyclosporine obtained from a soil fungus is used in organ transplantation for preventing transplant rejection; and ergotine to relieve one kind of headache migraine. Griseofulvin is used to inhibit fungal growth.
- Some natural dyes obtained from lichens are used in textile industry.
- Yeasts are heavily used in genetic/molecular biological research because of their rapid generation and rapidly increasing pool of genetic and biochemical information. Yeast were the first eukaryotes to be used by genetic engineers. In 1983, a functional artificial chromosome was made in Saccharomyces cervisiae. The same yeast was the first eukaryote whose genomic sequence was completely studied in 1996. Yeasts are also being investigated for production of some hormones. Pink bread mold Neurospora has also been used for genetic research.
Economic losses due to fungi
- Fungi are responsible for many serious plant diseases because they produce several enzymes that can breakdown cellulose, lignin and even cutin. All plants are susceptible to them. Extensive damages dueto rusts and smut diseases of wheat, corn (Fig. 8.15) and rice prompted mass displacement, and starvation to death of many people.
Powdery mildews (on grapes, rose, wheat etc), ergot of rye, red rot of sugar cane, potato wilt, cotton root rot, apple scab, and brown rot of peaches, plums, apricots and cherries are some other common plant diseases caused by fungi.
Fig. 8.15: Plant pathogenic fungus. Corn smut on an ear of sweet corn is caused by Ustilago maydis.
- Fungi also cause certain animal diseases. Ringworm and athlete’s foot are superficial fungi infections caused by certain imperfect fungi. Candida albicans, a yeast, causes oral and vaginal thrush (candidiasis or candidosis). Histoplasmosis is a serious infection of lungs caused by inhaling spres of a fungus which is common in soil contaminated with bird’s feces. If infection spreads into blood stream and then to other organs (which is very occasional), it can be serious and even fatal. Aspergillus fumigates causes aspergillosis, but only in persons with defective immune system such as AIDS, and may cause death. Some strains of Aspergillus produce one of the most carcinogenic (cancer-causing) mycotoxins (toxins produced by fungi), called aflatoxins. Aspergillus contaminates improperly stored grains such as peanuts and corn etc. milk, eggs and meat may also have small traces of aflatoxins. Any moldy human food or animal forage product should be discarded. Ergotism is causedby eating bread made from purple ergot-contaminated rye flour. The poisonous material in the ergot causes nervous spasm, convulsion, psychotic delusion and even gangrene.
- Saprobic fungi are not only useful recyclers but also cause incalculable damage to food, wood, fiber, and leather by decomposing them. 15-50% of world’s fruit is lost each year due to fungal attach. Wood-rotting fungi destroy not only living trees but also structural timber. Bracket/shelf fungi (Fig. 8.16) cause lot of damage to stored cut lumber as well as stands of timber of living trees.
A pink yeast (Rhodotorula) grows on shower curtains and other moist surfaces.
Fig. 8.16: This shelf fungus is parasitizing a tree. These are important decomposers of wood.