Morphology, Classification, Reproduction/Replication and Cultivation of Fungi

The organisms that grow on plants or animals are heterotrophic, which means that they need organic compounds to grow. Eukaryotes that produce spores are fungi. Their cells may be multicellular or unicellular. Yeast and moulds are examples of fungi. Fungi are usually studied as part of mycology.

Distribution

• Various habitats are hosts to this fungus, including aquatic and terrestrial (where it grows in soil, on decaying and dead materials).
• The fungus can also grow on animals and plants.
• Some grow in the air as well.
• For food, fungi lack chlorophyll, so they rely on other organisms. Hence, they can function as saprophytes, parasites, or symbionts.

Morphology

• Bacteria are generally smaller than yeast cells.
• Yeast that ranges from 1 to 5 micrometers wide and 5 to 30 micrometers long.
• A yeast does not contain flagella or other loco-motional organelles.
• Chitin and glucans are the main components of fungi's cell walls.
• A hyphal network is a network of long filamentous branched structures found in multicellular fungi.
• Mycelium, or thread like networks of hyphae, often form
• In lower fungi, there are no cross-walls; in higher fungi, there are septa that divide compartments.

Reproduction

Asexual reproduction

• Fungi may reproduce asexually or sexually.
• Neither sex cells nor sex organs are involved nor are nuclei united.
• It may be accomplished by:
• Budding of spores or somatic cells
• Spore formation
• Disjoining of hyphal cells or fragmentation
• Fission of somatic cells

Sexual reproduction

• During this process, the genetic material from two parents' cells is fused together.
• There are three stages of sexual reproduction:

1. Plasmogamy – Fusion of two protoplasts by joining two cells.
2. Karyogamy - This is when haploid nuclei fuse together.
3. Meiosis - During meiosis, chromosomes are reduced to haploid numbers.

• In fungi, gametangia are the sex organelles.
• Male gametangia are antheridium.
• The female gametangia is oogonium.

Sexual spores come in a variety of types

• The ascospore is a single-celled spore produced in a sac called an ascus.
• Single-celled basidiospores are found on basidium-shaped structures called basidia.
• Xygospores/zygosporangia are the result of the fusion of two sexually compatible hyphae or gametangia. They are large, thick-walled spores.
• By fertilizing oospheres with male gametes, oospores form within Oogonium.

Classification of fungi

A fungus can be classified into four major groups:

Zygomycota

• They are called zycomycetes.
• They inhabit terrestrial habitats.
• Monoploidy.
• The motile stage is absent.
• Zygospores are sexual spores.
• The asexual spores are sporangiospores and chlamydospores.
• Facultative parasite - Parasitic relationship.
• Rhizopus stolonifer, black bread mould, as an example.

Basidiomycota

• This fungus is commonly known as club-fungi or basidiomycetes.
• This species of fungus lives in terrestrial environments.
• Monoploidy and Dikaryotic.
• Motile stage– It does not exist.
• Arthrospores, oidia, conidia are all asexual spores.
• Basidiospores– Sexual spores.
• Parasite relationships can be facultative or obligate parasite.

Chytridiomycota

• These are commonly called chytrids.
• Terrestrial or aquatic habitat.
• Diploidy.
• The motile stage is present.
• Obligate parasites- Pathogenic relationship.
• The asexual spore is holocarpic.

Ascomycota

• Known as sac fungi or ascomycetes.
• Terrestrial in nature.
• Monoploidy.
• The motility stage doesn't exist.
• Sexual spores are ascospores.
• Non-sexual spore– Conidia.
• A pathogenic relationship is either facultative or obligatory.

Cultivation of fungi

Bacteria grow faster than most fungi. Bacterial cultures are grown on normal bacterial culture media at temperatures of 20-30°C. An acidic medium (pH 5.6) containing high sugar content is tolerant of molds. Molds and some yeast can be isolated using glucose- and peptones-containing media. Another well-known media for the culture of fungi is solid Sabouraud agar media, which contains maltose and peptone with less agar. A pH of 5.5 makes the media acidic, inhibiting bacterial growth. The isolation of fungi can also be accomplished using Potato Dextrose Agar, Brain Heart Infusion, and Czapekdox Agar media.

Mycelial fungi grow as filaments as opposed to yeast colonies. A yeast colony forms: Cryptococcus neoformans, for example. An organism that resembles yeast: Example: Candida albicans. The colony of a hyphomycete is called a dermatophyte. The media containing chloramphenicol and cycloheximide can support saprophytic growth of fungi. Dimorphic fungi can be differentiated with Papanicolaou stain at the outset. Gram-positive fungi are most common, while Gram-variable fungi are Nocardia and actinomyces.

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