Describe structure and life cycle of Aspergillus (Eurotium)

It belongs to class Ascomscetes. It is common black mould. Most species grow as saprophytes on fruits, cheese, syrups, Jams, Jellies, dung and leather. They cause damage to our exposed food. Some species like A niger and causing pulmonary disease aspergollosis.

Plant body of Aspergillus is much branched separate mycelium. Mycelium bears bright or pale hyphae lying on substratum. Hyphae are much branched and separate. Each cell is multi nucleate and has mass of granular protoplasm and oil globules.

Reproduction: Reproduction takes place by vegetative, Asexual and Sexual methods.

(1) Vegetative Reproduction: It takes place by fragmentation.

(2) Asexual Reproduction: It takes place during favourable conditions of growth and nutrition by condiospores. From mycelium arise stout, erect and unseparate conidiospores.
Free end of conidiospore swells up into a vesicle. Many small and bottle shaped hyphal outgrowthst the sterigmata are budded out from the vesicle and covers its entire surface. Many nuclei from conidiospore pass into sterigma. Sterigmata may be branched or un-branched and may also form secondary sterigmata. Each sterigmata bud off a chain of conidia. Each conidium or conidisopore in a small, oval, greenish uni or multi nucleate structure. On maturity the conidia or conidiospore are distributed by air. When they reach the substratum, the spore germinates to form a hypha which develops into fresh mycelium.

(3) Sexual Reproduction: It is rare and takes place in favourable conditions. Sex organs are produced on the same mycelium which has produced conidia. Male organs called Antheriduim or Pollinoduim and female as archicarp or Ascogonium Female organs achicarp develop as a branch of hypha. This branch is coiled and the coils are loose but later come closer.

Septa are formed and each cell becomes multinucleate. The apical segment is called trichogyne, the next one oogonium and the lower separate part is stalk. The antheridium or male organ arises as brighter near archicarp either from the same hypha which bears ascogonium or from an adjacent one. It is separate and the segments are multinucleate. The terminal or apical segment is the antheridium proper while the lower separate part acts as stalks.

Dikaryotization: The antheridium curves round and bend towards the apex of archicarp. Two become spirally coiled and their tips may get fused. Contents of antheridium pass down into ascogonium and nuclei become paired i.e. one antheridial one ascogonial nuclei is each pair. After pairing they separate, segments are bi-nucleate, each segment laterally produces a hypha called ascogenous hypha which are separate and each cell of ascogenous hypha is uni-nucleate. Two nuclei form diploid zygonic nucleus which divide by meiosis into shaploid nuclei which form sascorpores which germinate into mycelium.

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