Aspergillus
Q.1. Write about the life history of Aspergillus and reproduction of Eurotium or Aspergillus. (1995, 96, 97)
Related Questions -
Q. Describe the life cycel of Aspergillus. (2002)
Q. Give the systematic position and structure of Aspsergillus. (2001)
Q. Write systematic position and important characters of Aspergillus. (2011, 13)
Q. Describe asaxual reproduction in Aspesrgillus. With the help diagram. (2001, 04, 06, 08)
Q. Describe sexual reproduction of Aspergillus. (2009)
Ans. Systematic Position: -
Kingdom - Mycota
Division - Eumycotina
Sub-division - Ascomycotina
Class - Plectomycetes
Order - Eurotiales
Family - Aspergillaeceae
Genus - Aspergillus
This is a common black mould. Most of species grow as saprophytes on different nutrient media such as fruits , chees, syrups, jelles, dung, leather etc. Some species as A. niger, A. flavus etc. are parasitic on animals and human beings casin g the pulmonary disease aspergillosis.
Structure: - The plant body consists of much branched septate mycelium. The mycelium consists of interwoven masses of bright or pale coloured hyphae which surface hyphae are much branched, multinucleate and contain a mass of granular protoplasm and oil globules.
Reproduction: - The plant body reproduces vegetatively, asexually and sexually.
Fig. - Mycellium and conidiophore
1. Vegetative reproduction: - It takes place simply by fragmentation.
2. Asexual reproduction: - During favourable condition asexual repro
duction takes place by conidiophores. Conidia are formed on conidiophores. In this reproduction mycelium arises as stout, erect and aseptate conidiophores. Conidia arranged in chain on conidiophores. Each conidium or conidiospore is a small, oval, greenish, multi or uninucleate strcture. On reaching maturity the conidia are disseminated by air and these spores germinate to from a hyphae which develops into new fresh mycelium.
3. Sexual Reproduction. Sexual reproduction is rare and the Sex organs develop on the same mycelium which has produced conidia. Male organs called antheridium or pallinodium and female as archicarp or ascogonium.
Ascogonium. (female branch) is coiled and the coils are loose in beginning but later come closer. Mycelium is septate and multinucleate. The apical segment is called as trichogyne and the next one is oogonium and lower part is called stalk.
Antheridium: - It is male reproductive develop on male branch near theascogonium orgem and is septate and the segments are multinucleate. Apical or terminal segments is antheridium and lower part is stalk.
Fig. Asexual reproduction.
Dikaryotization: - Antheridium curves round and bends towards the apex of ascogonium. Both become spitally coiled and their tips get fused and their nuclei become paired. One antheridial and other one ascogonial nuclei in each pair.
Formation of fruiting body or cleistothecium or Ascocarp. After dikaryotization the ascogonium develops into a fruiting body or the fruitification which is called ascocarp. Ascocarp becomes sepatate and binucleate. Each segment produces a hypha called ascogenous hyphal. After this ascogonous hypha behave as an ascus mother cell or ascus. The diploid nuclei of ascus divide by reduction division (meiosis ) and two simple divisions form 8 haploid nuclei which later form 8 ascopores.
Ascogonium two layered wall of peridium of ascocarp known as cleistothecium. Cleistothecium consists of large number of ascipseudoparenchymatous tissue and peridium wall. The ascospores are liberated ands germinated into new mycelia.
Fig. Life cycle of Aspergillus
Q.3. Write short note on parasexuality. (2009, 11)
Ans. Parasexual Cycle or Parasexuality: -
In some fungi true sexual cycle comprising of nuclear fusion and meiosis is absent. These fungi derive the benefits of sexuality through a cycle known as parasexual cycle.
The parasexual cycle is defined as a cycle in which plasmogamy, karyogamy and meiosis ( haplodisation ) take place but not at a specified time or at specified points in the life cycle of an organism. Generally parasexual cycle occurs in those fungi in which true sexual cycle does not take place. The members of class Deuteromycetes in which sexual cycle does not occur, exhibit parasexual cycle generally.
Parasexual cycle was first discovered by Pontecarvo Larvo and Roper of University of Glasgow in 1952 in Aspergillus nidulans, the imperfect stage of Emericella nidulans. Since then parasexual cycle has been discovered not only in members of Deuteromycetes but also in fungi belonging to Ascomycetes and Basidiomycetes. Parasexual cycle is also known as somatic recombination.
Q.4. Write a note on Economic Importance of Aspesrgillus. (2011)
Ans. Economic Importance of Aspergillus:-
About 33 species of Aspergillus are found in India. Some species of Aspergillus are very useful to man and some are harmful to man as well as plants.
Harmful Activities:-
(1) Many species of Aspergillus, e.g. , A. glaucus, A. flavus and A. repens are responsible for the spoilage of exposed foodstuffs, jams and other sugary substances, leather, textiles, tobacco, cigars and many other organic products.
(2) Some species of Aspergillus, e.g. , A. flavus, A. fumigatus and A. niger cause diseases of animals and human beings. These diseases are known as aspergilloses. This disease is much more common in birds but also occurs in cattle, sheep, horses and in human beings. The symptoms of aspergillosis in lungs resemble with that of tuberculosis.
(3) Some species, e.g. , A. fumigatus, A. flavus and A. niger are responsible for causing the diseases of human ear. This disease is called Otomycosis.
Useful Activities:-
(1) Several species of Aspergillus are important in cheese manufacture.
(2) A. oryzae is used in the preparation of wine from rice and soyabean sauces.
(3) A. niger can detect the copper even in traces, hence it is used in bio-assays.
(4) Some species of Aspesrgillus, are the source of certain antibiotics such as Flavicin, Aspergillin, Geodin, Funagalin, Patulin and Ustin etc.
(5) A. gossypii is used in the production of vitamin B.
(6) Some species are used in the production of fats.
(7) Several species of Aspergillus are used for the industrial production of organic acids like citric acid and gluconic acid.