Fungi

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 kingdom fungi.
  • They are generally grown in moist and warm places.
  • Fungi are usedl in food industry (Yeast), agriculture (Mycorrhiza) and in 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 intertwining 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, 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, water and parasitic on plants as well as the animals.
  • These are non chlorophyllous organisms and hence cannot perform photosynthesis. .
  • They may be multicellular, unicellular or filamentous.
  • These are heterotrophic may be Saprophytes (feed on dead organic substance) or Parasites (live on other living organisms like plants and animals and absorbs nutrients from their host).
  • These are spore producing achlorophyllous organisms like mildew, Rhizopus, Mucor, Rusts bracket Fungi, Morels & Mushrooms.
  • Fungi cause diseases: example- Rust is caused by Puccinia, the smut is caused by Ustilago. Penicillium produces antibiotic.
  • Fungi store their food in the form of starch.
  •  Fungi make symbiotic association with algae in Lichens.
  •  Fungi reproduce by sexually or asexually.
  • Spore producing bodies are known as the fruiting bodies.
  • Some common examples are yeast, moulds 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.
  • Zygospore is formed by fusion of two gametes. These gametes are similar in morphology (isogamous) or dissimilar (anisogamous or oogamous).
  • Some common examples are Mucor, Rhizopus (the bread mould) 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, example rusts and smuts.
  • The mycelium is branched and septate.
  • Specifically the Basidiomycota include mushrooms, puffballs, stinkhorns, bracket fungi, 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 BASIDOMYCETES

            

                          Agaricus                                                   Puccinia

Deuteromycetes

  •  There are about 25,000 species that have been classified in the Deuteromycota.
  • The Deuteromycota (Greek for "second fungi") were 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 sexual or perfect stage is absent in 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 fungus 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 sexually and asexually means.

  • Vegetative reproduction takes place by budding, fragmentation and fission.
  • Asexual reproduction takes place through conidia spores or 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.
  • Yeast 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.