General Characteristics and Reproduction of Fungi

General Characteristics of Fungi

• Fungi are heterotrophic, meaning they lack photosynthesis and obtain nutrition through absorption.
• Fungi typically have a vegetative state as a non-motile mycelium of hyphae. They may also feature motile reproductive stages.
• Fungi have cell walls, typically composed of glucans and chitin (Oomycetes may have glucans and cellulose).
• Fungi are eukaryotic, and their thalli can be uninucleate or multinucleate, homokaryotic, heterokaryotic, haploid, dikaryotic, or diploid, though diploid stages are often short-lived.
• Fungi exhibit diverse life cycles, ranging from simple to complex.

Reproduction in Fungi

• Fungi reproduce sexually (nuclear fusion and meiosis), parasexually (nuclear fusion followed by gradual diploidization) and asexually (purely mitotic nuclear division).
• Asexual reproduction involves various spore types, including zoospores (motile), sporangiospores (non-motile), conidia, and budding (common in unicellular fungi).
• Sexual reproduction occurs through isogamy (gametes indistinguishable), anisogamy (gametes different sizes), or oogamy (female gamete is large and stationary.) Different spores are produced, including zygospores, oospores, ascospores, and basidiospores.

Beneficial Effects of Fungi

• Fungi contribute to nutrient and carbon recycling through decomposition.
• Fungi are used in industrial processes for producing alcohols, fats, citric acid, oxalic acid, and gluconic acid.
• Fungi are a source of antibiotics (e.g., penicillin).
• Fungi are model organisms for biochemical and genetic research, including applications like the Hepatitis B Vaccine.
• Some fungi are edible (like mushrooms).
• Fungi produce nutritional supplements like vitamins and cofactors.
• Some fungi are important in food flavoring (e.g., Roquefort and Camembert cheeses).
• Certain fungi produce medically important alkaloids, helping with uterine contractions, bleeding control, and migraine treatment.
• Some fungi are used to control mosquitoes (e.g., malaria vector control, using specific fungal types).

Harmful Effects of Fungi

• Fungi can damage food, lumber, paper, and cloth.
• Fungi can cause animal and human diseases, including allergies.
• Some fungi produce toxins in poisonous mushrooms. These occur in food as well (mycetism, mycotoxicosis).
• Fungi cause plant diseases.
• Fungi cause spoilage of agricultural products like vegetables and cereals.
• Fungi can damage various materials like magnetic tapes, glass, marble statues, bones, and wax.

Classification of Fungi

• Some mycologists classify fungi based on evolutionary origins, placing them within the plant kingdom as they have lost chlorophyll.
• Other mycologists classify fungi as a separate kingdom, distinct from plants and animals, arising from protozoa in early evolution.
• Based on the presence or absence of plasmodium and pseudoplasmodium, fungi are often divided into Myxomycota (slime molds) and Eumycota (true fungi).
• Eumycota is further divided into various classes based on sexual reproduction types, spore type, septa in the mycelium, etc.

Mastigomycotina (oomycetes)

• Some oomycete members have sac-like or branched thalli.
• Oomycetes produce hyphae that form a mycelium.
• Oomycete hyphae feature apical growth, enzyme secretion, and the formation of specialized structures like appressoria or haustoria.
• Oomycete hyphae are typically coenocytic (lack septa).
• Oomycete cytoplasm contains vacuoles, Golgi stacks, mitochondria, and diploid nuclei.

Albugo

• Albugo are a monogenetic family of biotrophic parasites on flowering plants.
• They cause white blisters or white rusts on various plants.
• A. candida is a common species associated with crucifers (like cabbage and turnips).
• The Albugo mycelium exists within the host tissue, forming intercellular hyphae and producing small spherical haustoria.
• Hyhpae in Albugo are interconnected via narrow stalks (about 0.5 mm wide).

Rhizopus

• Rhizopus are saprophytic and parasitic fungi, common in damp and moist environments and associated with organic materials like vegetables, fruits, bread, jellies.
• Rhizopus mycelium is coenocytic and branched.
• Rhizopus mycelium is made of three hyphae types; stolon, rhizoids, and sporangiophores.
• Stolons are aerial hyphae that form arches and touch the substrate for nodal growth.
• Rhizoids are branched hyphae attached to the substrate to assist in absorption.
• Sporangiophores are reproductive hyphae that produce sporangiospores.

Rhizopus Life Cycle (Asexual and Sexual)

• Rhizopus reproduces through asexual and sexual reproduction.
• Asexual Reproduction: Occurs via the formation of sporangiospores (formed terminally in sporangia on sporangiophores) under favorable conditions.
• Asexual Reproduction: Also occurs via chlamydospores, which are thick-walled spores formed in unfavorable conditions. Spores detach from the mycelium when dry.
• Sexual Reproduction: Involves fusion of compatible hyphae from (+) and (-) strains. Progametangia form (outgrowths), followed by gametangia fusion (plasmogamy), karyogamy to form a diploid zygospore.
• Zygospores then develop, germinate, and undergo meiosis to form haploid meiospores, enabling them to spread to new environments