SUB DIVISION ASCOMYCOTINA
Class plectomycetes
Order Eurotiales
Members of order eurotiales show gradual reduction of sexuality . Conidia give a characteristic tint to the fungus .
Aspergillus ( Eurotium )
Sub division - Ascomycotina
Class - Plectomycetes
Order - Eurotiales
Family - Eurotiaceae ( Aspergillaceae )
Genus - Aspergillus
A. flavus produces aflatoxins which are carcinogenic in nature . It contaminates food stuffs like groundnuts . Citric acid is obtained from fermantation of sugar by aspergillus .Mycelium is profusely branched , septate and multinucleate . Foot cell of somatic hyphae forms erect branch called conidiophore which swells at the tip , accumulates cytoplasm and forms a vesicle . Shape of vesicle differs in different species of aspergillus . Several finger shape projections called phialides or sterigmata develop on vesicle . First layer is primary sterigmata and subsequent layers are secondary and tertiary sterigmata . Conidia develop exogenously in long basipital chains on sterigmata .
Most of the species of aspergillus are homothallic but few are heterothallic . Male sex organ is unicellular antheridia ( Antheridia is not a common feature of all species of aspergillus ) and female sex organ is ascogonium . Ascogonium has terminal receptive region trichogyne and unicellular ascogonium . Fertilization takes place by gametangial contact between antheridia and trichogyne and results in formation of a dikaryon in ascgonium .
Dikaryon develops into a ascogenous hypha by septation .Terminal cell of ascogenous hypha curves to from a hook like structure crozier . The two nuclei of dikaryon in crozier divide to form 4 daughter nuclei . Now septa is formed in crozier in such a way that the basal cell has 1 nuclei , penultimate cell has 2 nuclei and terminal cell has 1 nuclei . Penultimate cell functions as ascus mother cell and elongates to form ascus . 2 nuclei of penultimate cell fuse to form a diploid nucleus which undergoes meiosis followed by mitosis . It results in formation of 8 haploid ascospores . At the same time cells below ascogonium form a layer called peridium . Peridium encloses ascogenous hyphae . It results in fruiting body called ascocarp . The ascocarp is completely closed cleitsothecium .
Sexual stage is called perfect state and sexual stage is called imperfect state . There are different names for these states . Eurotium , Emericella etc are perfect states of aspergillus .
Penicillium
Classification and life cycle are same as of Aspergillus . Penicillium is commonly known as blue or green mold . Latin word Penicillus means artists brush , penicillium shows brush like appearance due to its branched conidiophores .
Penicillin was discovered by Alexander Fleming in 1929 . Wonder drug penicillin is commonly obtained from P. chrysogenum and P. notatum , griseofulvin is obtained from P. greseofulvin . P. rocqueforti and P. camembertile are used in cheese industry .
Mycelium is profusely branched , septate , uni to multinucleate . Branched conidiophores have ramus , metulae , phialides ( sterigmata ) and conidia in a sequence according to type of species . In some species sex organs do not develop at all . Most of the species of Penicillium are homothallic but few are heterothallic . Antheridium coils spirally around the ascogonium . Fertilization takes place by gametangial contact . Ascocarp is cleistothecium type as in aspergillus . Perfect stage of penicillium are Talaromyces , Eupenicillium .