Penicillium, Candida and Molds and their associations with other organisms

Penicillium (Class Deuteromycetes)

Members of this group, also Deuteromycetes, occur widely in nature. Some species cause rot or other spoilage of fruits, vegetables, preserves, grains, and grasses. Others are used in the ripening of cheese,e.g., Roquefort, blue, and Camembert. Some are used in industrial fermentations, and one of the best-known antibiotics (penicillin) is produced by P. Notanum and P. Chrysogenum. These molds are closely related to the Aspergilla, and some reproduce sexually by ascospore formation. Ascus formation is observed in the Penicillia less commonly than in Aspergilla. The conidial stages of penicillium and Aspergillus are so distinct and well known that they are discussed on that basis rather than on their perfect stages.

Penicillium has septate vegetative mycelia which penetrate the substrate and then produce aerial hyphae on which conidiophores develop. Conidiophores may be branched and have the brush like heads bearing spores. Clusters of sterigmata are usually in one place, and form each is formed a chain of conidia. The color of the mature plants is useful in helping to identify species. They grow best at the temperature ranging from 15 to 30.

Candida (Class Deuteromycetes)

Candida albicans is often isolated from warm-blooded animals, including humans, where it exists as part of the normal microbiota of mucous membranes. Sometimes this fungus may become pathogenic,causing candidiasis, a disease of the mucous membranes of the mouth (thrush), vagina, and alimentary tract. More serious infections can involve the heart (endocarditis), the blood (septicemia), and the brain (meningitis). It seems that predisposition factors such as other diseases, physiological disorders, obesity, alcoholism, and prolonged use of broad-spectrum antibiotics and steroids can create conditions in which C. Albicans can cause disease. This makes the fungus an opportunistic pathogen.

Molds and their associations with other organisms

There are some interesting partnerships in nature involving a mold and some other organism. In some of these associations the partners are dependent on each other and cannot survive alone. In others, the individuals can survive independently.

Lichens

Lichens are composite organisms composed of fungi and algae, each contributing to the benefit of both. The algae synthesize carbohydrates by photosynthesis and obtain other nutrients from the fungi; the fungi depend on the algae for organic carbon.

Fungi and nematodes

Nematodes are small round worms predominantly pathogenic for plants; some may be parasitic in humans and other animals, and some are saprophytes. Plant pathogenic nematodes live in the soil, where they destroy roots and other underground parts of plants. One of their greatest natural enemies is certain fungi that thrive on a diet of nematodes. These fungi use interesting techniques to capture and overcome the much larger nematodes. One of the most unusual techniques employs a loop of fungal hyphae. Upon contact by the nematode, the loop constricts around the body of the worm and holds it firmly while penetrating the prey with haustoria (special hyphal branches that penetrate a host cell) which will digest the nematode’s, rotifers, and protozoa in the soil involve an adhesive on the mycelium. Still another fungal snare is a complex network of mycelia which grasps the worm as it tries to penetrate the fungal barrier.

Fungi as parasites of insects

Not all associations of fungi with higher organisms are beneficial to the host. Common among the detrimental associations is fungal infections of insects, of which more than 50 are known. At times, some appear as epidemics, when they destroy large numbers of insect host. The fungus Entomophthora muscle has been the cause of mild epidemics among common houseflies, cricket, and grasshoppers. Such epidemics are self-limiting can only rarely be used effectively to destroy insects pastes; e.g., pathogenic fungi which attack aphid infestations of citrus orchards have been used in attempts to develop the biological method for insects pests.

Mycorrhizas

A Mycorrhiza is an infected root system arises from the rootlets of a seed plant. The Mycorrhiza is derived from the Greek, meaning “fungus root.” This association is usually beneficially to the host plant as well as the symbiont, and sometimes the host cannot thrive without the benefit derived from the fungus. Mycorrhizas enhance mineral absorption by the green plants. Host plants usually have a built-in check on the fungus to prevent it from causing injury to the rootlets. Truffles are subterranean fruiting bodies of certain A. ascomycetes which grew in association with some trees, oak, and beech being common symbionts in this Mycorrhizal partnership. The fungus provides certain nutrients to the tree, which in turn provides essential growth substance to the fungus. Such relationship is quite common. Truffles consists of a mass of ascospores and mycelia, cover with a thick nobby rind of mycelium. They have a pleasant odor, flavor, texture which makes them highly prized by gourmets.

In plants, that do not have roots hairs, e.g., orchids, the fungi observed nutrient and water for their host. Under natural condition, orchids rarely grow without fungal partners. Experimentally, the orchid will grow alone if appropriate nutrients are provided.

Another type Mycorrhizas is found in Monotropa uniflora (Indian pipe), which has no chlorophyll but grow well in the heavy shade of the forest floor as long as the fungi are on its roots to gather food for both host and parasite.

References

Arvind, Keshari K. and Kamal K Adhikari. A Textbook of Biology. Vidyarthi Pustak Bhander.

Michael J.Pleczar JR, Chan E.C.S. and Noel R. Krieg. Microbiology. Tata Mc GrawHill, 1993.

Powar. and Daginawala. General Microbiology.

Rangaswami and Bagyaraj D.J. Agricultural Microbiology.