Cultivation of fungi

Cultivation of fungi

General cultural methods used for thestudy of bacteria can even be applied for the appropriate study of molds and yeasts. Nearly all of the fungal species grow aerobically on the usual bacteriological culture media at temperatures between the ranges of 20 to 30-degree celsius,however, most of them grow more slowly compared to bacteria so that media which support bacteria, as well as fungi, may be overgrown by bacterial contaminants in a mixed inoculum. When fungi are to be isolated, it is better processed to use a medium that favors their growth but is not optimal for the growth of bacterial species. Media with acidic PH(pH 5.6) that incorporate a relatively high concentration of sugar are well tolerated by molds but are not tolerated too many bacteria.

Sabouraud devised One of the best-known and oldest media for the growth of fungi which contains maltose and peptone as its principal ingredients. Most commonly glucose and any one of several specified peptones containing modified media are used in countries like America . This medium can be usedwidely for the isolation of molds and certain yeasts and is relatively useful for growing pathogenic fungi from infected body fluids and exudates. Its partial selective action occurs due to the presence of high sugar concentration as well as low pH in the concerned medium.

Most parts of the molds being potentially capable of growth, inoculation of even a small fragment of mycelium on a medium can be sufficiently enough to start a new mold colony. This task can better be accomplished by planting the inoculum on a fresh medium with the help of a transfer needle. This method can be used commonly for both molds and bacteria. The only difference in the process is that the needle used for molds is stiffer and has a flattened tip for cutting the mycelium whereas, an ordinary inoculating loop used for bacteria is suitable for the inoculation of yeasts.

Classification of fungi

Unlike that of bacteria, the classification of fungi is based chiefly on the characteristics of the sexual spores and fruiting bodies present during the sexual stages of life cycle of the fungal species. However, in many cases, fungi are found to be producing sexual spores and fruiting bodies only under certain environmental conditions, if they are known to produce them at all. Thus the complete or perfect life cycles of many fungi are yet not known. Thus, fungi whose lifecycle has not been perfectly or completely described must be classified on thebasis other than the characteristics of their sexual stages. The structure and morphology of their asexual spores and thalli then become more significant- until that their sexual traits are become completely and perfectly identified, which requires re-evaluation of their taxonomic status. Thus these imperfect higher fungi have been provisionally kept in a special class called form-class Deuteromycetes. Almost all of the sexual stages found subsequently among members of this class are generally of the ascomycete type. In case sexual stages are found, the organisms can be classified again and placed in with the ascomycetes or basidiomycetes groups.

We should be aware that all cannot be included in themycological classification and that different opinion on classification exists. Incomplete knowledge of the structure, development, and physiology of fungi results in the arousal of divergent views in the field of their classification. Therefore classification schemes are bound to change with the development of our knowledge about the fungi.

Taxonomy of the fungi is in accordance with the recommendations of the committee on International rules of Botanical Nomenclature. Accordingly, the various taxa are known to have endings as follow:

Divisions: Mycota

Subdivisions: Mycotina

Classes: Mycetes

Subclasses: Mycetidae

Orders: ales

Families: aceae

Genera and species do not have any standard endings.

Some fungi of special interest

Most of the properties, activities, and characteristics of fungi can best be described by the help of the various example. The following are some of the genera most commonly encountered in microbiology. Among them, these are some of the most interesting to microbiologists because of their unique biological properties or due to particular economic or medical importance.

Synchytrium (Class Chytridiomycetes)

More than 100 species of this genus are found to be parasitic on flowering plants. Many species are not very harmful to the host plant, but the formation of galls on leaves, stems, and fruits are the common symptoms of their effect. The most serious parasite found to be infecting plants is S. Endobioticum that causes the black wart disease of potato. Dark warts on the potatoes are as the result of galls in which the host cells have been stimulated to divide by the infection of fungi. The resting sporangia can be released by the decay of warts and they might remain alive for many years in the soil. The zoospores released from a sporangium are able to swim continuously for about two hours in soil water until they find a new host tuber to infect. The zoospores may also combine to form zygotes which finally retain their flagella and swim actively for a significant amount of time. The zygote then encysts on the surface of the host epidermis and penetrates the host cell in order to infect it. The results of zygote infection vary from infection by zoospores. When infected by a zoospore, the host cell fights back by undergoing hypertrophy, i.e., an increase in cell volume, and adjacent cells also enlarge to form the characteristic rosette. When infected by a zygote. The host cell transform into hyperplasia, i.e., continuous and repeated cell division resulting in the formation of the characteristic wart. Control of such wart disease is generally based largely on the breeding varieties of potatoes.

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.