Kingdom Fungi

What is Fungi?

  • They are eukaryotic, non-vascular, non-motile, and heterotrophic organisms that include microorganisms like Yeast, Mucor, Agaricus, etc.
  • These organisms are placed under the kingdom of fungi.
  • They are generally grown in moist and warm places.
  • Fungi are used in the food industry (Yeast), agriculture (Mycorrhiza), and medicine (Penicillin).

Structure of Fungi

  • They are mostly multicellular filamentous organisms except yeast which is unicellular.
  • Their body consists of long thread-like bodies called hyphae.
  • Hyphae are of two types – Septate and Coenocytic
  • These hyphae, all intertwine to make up a tangled web called the mycelium.
  • Fungi have a cell wall, made up of chitin and polysaccharides.
  •  As eukaryotes, fungal cells contain a membrane-bound nucleus where the DNA is wrapped around histone proteins.
  • The nucleus is dense, and clear, with chromatin threads. The nucleus is surrounded by a nuclear membrane.

         

             Structure of Fungi             Types of Hypae

Characteristics of Fungi

  • They are eukaryotic, non-vascular, non-motile, and heterotrophic decomposers.
  • A fungus occurs in soil, air, and water, and is parasitic on plants as well as animals.
  • These are nonchlorophyllous organisms and hence cannot perform photosynthesis.
  • They may be multicellular, unicellular, or filamentous.
  • These are heterotrophic and may be Saprophytes (feed on dead organic substances) or Parasites (live on other living organisms like plants and animals and absorb nutrients from their host).
  • These are spore-producing achlorophyllous organisms like mildew, Rhizopus, Mucor, Rusts bracket Fungi, Morels, and mushrooms.
  • Fungi cause diseases: for example- Rust is caused by Puccinia, the smut is caused by Ustilago. Penicillium produces antibiotics.
  • Fungi store their food in the form of starch.
  •  Fungi make a symbiotic association with algae in Lichens.
  •  Fungi reproduce sexually or asexually.
  • Spore-producing bodies are known as the fruiting bodies.
  • Some common examples are yeast, molds, and mushrooms.

Classification of Fungi based on Spore Formation

  • Fungi can be classified into four groups based on the formation of spores:
    • Phycomycetes
    • Ascomycetes
    • Basidiomycetes
    • Deuteromycetes

Phycomycetes

  • Members of Phycomycetes are found in aquatic habitats and feed off of plant detritus or decaying animal material.
  • They also cause problems by growing on human food sources.
  • The mycelium is aseptate and coenocytic.
  • Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-motile). These spores are endogenously produced in sporangium.
  • A zygospore is formed by the fusion of two gametes. These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).
  • Some common examples are Mucor, Rhizopus (the bread mold), and Albugo (the parasitic fungi on mustard).

EXAMPLES OF PHYCOMYCETES

    

                       Rhizopus                                       Mucor

Ascomycetes

  •  The Ascomycota are a Division/Phylum of the kingdom Fungi and subkingdom Dikarya.
  •  Members of these groups are commonly known as the Sac Fungi.
  •  They are the largest phylum of Fungi, with over 64,000 species.
  •  The defining feature of this fungal group is the “Ascus", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed.
  •  Some species of the Ascomycota are asexual, meaning that they do not have a sexual cycle and thus do not form asci or ascospores.
  •  The ascomycetes are a monophyletic group, i.e., all of its members trace back to one common ancestor.
  •  They are saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
  •  Mycelium is branched and septate.
  • The asexual spores are conidia produced exogenously on the special mycelium called conidiophores. Conidia on germination produce mycelium.
  •  Sexual spores are called ascospores which are produced endogenously in sac-like asci (singular Ascus). These asci are arranged in different types of fruiting bodies called ascocarps. Some examples are Aspergillus, Claviceps, and Neurospora.

EXAMPLES OF ASCOMYCETES

        

                Aspergillus                                   Claviceps

Basidiomycetes

  • Basidiomycota are filamentous fungi composed of hyphae (except for those forming yeasts) and reproduce sexually via the formation of specialized club-shaped end cells called basidia that normally bear external meiospores (usually four). These specialized spores are called basidiospores.  
  • They grow in soil, on logs and tree stumps, and in living plant bodies as parasites, for example, rusts and smuts.
  • The mycelium is branched and septate.
  • Specifically, the Basidiomycota include mushrooms, puffballs, stinkhorns, bracket fungi, and other polypores.
  • Karyogamy and meiosis take place in the basidium producing four basidiospores. The basidiospores are exogenously produced on the basidium (pl.- basidia). The basidia are arranged in fruiting bodies called basidiocarps. Some common members are Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).  
  •  Asexual reproduction takes place by fragmentation, budding, oidia, conidia or chlamydospore.

EXAMPLES OF BASIDIOMYCETES

      

                     Agaricus                                                  Puccinia

Deuteromycetes

  •  There are about 25,000 species that have been classified in the Deuteromycota.
  • The Deuteromycota (Greek for "second fungi") was once considered a formal phylum of the kingdom Fungi.
  • Some of them are unicellular while others are multicellular.
  •  They are commonly known as Fungi imperfecti or imperfect fungi because the sexual or perfect stage is absent in the life cycle.
  • Fungi producing the antibiotic penicillin and those that cause athlete's foot and yeast infections are imperfect fungi.
  •  Only their asexual form of reproduction is known, meaning that this group of fungi produces their spores asexually.
  • They reproduce asexually by conidia along with some other types of spores.
  • The mycelium is septate and branched.
  • There are a number of edible imperfect fungi, including the ones that provide the distinctive characteristics of Roquefort and Camembert cheese.
  •  Some members are saprophytes or parasites while a large number of them are decomposers of litter and help in mineral cycling. Some examples are Alternaria and Trichoderma

 EXAMPLES OF DEUTEROMYCETES

                   

                  Alternaria                                        Trichoderma

Reproduction in Fungi

Fungi reproduce through both sexual and asexual means.

  • Vegetative reproduction takes place by budding, fragmentation, and fission.
  • Asexual reproduction takes place through conidia spores zoospores, or sporangiospores.
  • Sexual reproduction takes place through ascospores, basidiospores, and oospores.
  • The process of sexual reproduction involves three phases:
    • Plasmogamy: fusion of protoplasm
    • Karyogamy: fusion of nucleus
    • Meiosis: reductional nuclear division

Uses of Fungi

  • Fungi have a crucial role in human life. In most ecosystems, fungi play a major role in decomposition.
  • The ascomycetes are relevant to humans as sources for medicinally important compounds, such as antibiotics, and for making bread, alcoholic beverages, and cheese, but also as pathogens of humans and plants.
  • The yeast is used in the making of bread and also produces vitamin B.
  • Neurospora is used extensively in biochemical and genetic work.
  • Antibiotics are produced naturally by fungi to kill or reduce the development of bacteria, hence reducing competition in the natural environment.
  • Fungi can be used to isolate important medicines like penicillin and cephalosporins.