Introduction:
Fungi is a group of non motile eukaryotes which exist as Saprophytes, parasites and symbiotics.
Fungi are placed in phylum Thallophyta which contains irregular plant masses that don't have a definite root, leaf and stem structures.
Fungi can be classified on many criterias like Morphology, Virulence, Medicinal importance, Spore production etc.
Morphological Classification of Fungi:
Depending on morphology fungi are classified into four classes as follows,
Moulds
Yeasts
Yeast like fungi
Dimorphic fungi.
Moulds and Fleshy fungi:
Also called “Filamentous fungi.
The fungi which form mycelia are called moulds.
Their “thallus” (Body) is made up of filament like cells which are joined together and are called “hyphae”.
Some hyphae have internal wall-like structures called “Septa” (Septum) which separates two uninucleate or multinucleate cell like structures, such hyphae are called “Septate Hyphae”.
Some hyphae which don't have septa are called “Coenocytic” or “Nonseptate hyphae”.
In suitable environmental conditions the hyphae grow to form a network called “Mycelium”.
The part of mycelium dealing with food production is called “Vegetative mycelium”, while the part of mycelium dealing with reproduction is called “reproductive or aerial mycelium”.
When grown on artificial medium they appear like filamentous dry powdery colony.
E.g. Aspergillus niger, Penicillium notatum.
Yeasts:
These are unicellular, round, oval or elongated fungi.
They reproduce by asexual method “Budding”.
In the culture medium they form smooth creamy colonies.
E.g. Saccharomyces cerevisiae
Difference between Mould and Yeast.
Yeast Like Fungi:
Some yeasts like Candida albicans
, the bud remains attached to the mother cell and elongates followed by repeated budding.
This gives the appearance of hyphae however, it can be differentiated easily as at septa they are constricted even at branching also it is observed.
On culture media they form moist cream colored colonies.
Dimorphic Fungi:
The fungi which exhibit two forms of growth i.e. as mould or as yeast are called dimorphic fungi.
Mainly pathogenic species exhibit dimorphism.
The dimorphism usually depends on Co2 and temperature.
At 25°C they grow like mould and at 37°C they grow like yeast.
E.g. Histoplasma capsulatum
Classification based on spore production:
Based on sexual spore production fungi are classified in four subclasses as follows,
Phycomycetes.
Ascomycetes.
Basidiomycetes.
Fungi imperfecti.
Phycomycetes:
Have nonseptate hyphae (Lower fungi).
Mostly produce asexual spores called “Sporingiospores”, in a sac like structure called “Sporangia”.
They also produce sexual spores like Zoospores and Zygospores.
E.g Mucor, Rhizopus.
Ascomycetes:
They form sexual spores called “Ascospores” in a sac like structure called “Ascus”.
They form septate hyphae.
Ascomycetes include both yeasts and moulds.
E.g. Claviceps purpurea (Ergot), Histoplasma, Candida etc.
Basidiomycetes:
Reproduce asexually and form septate hyphae.
They produce “Basidiospores”.
Fungi imperfecti:
Also Called Deuteromycetes or Hyphomycetes.
This group consists of fungi whose sexual phases are not been identified properly.
e.g. Trichophyton, Epidermophyton.