Fungi Kingdom and Slime Molds

Kingdom Fungi

• Fungi are heterotrophic organisms that obtain nutrients by absorption
• Cell walls are mostly made up of carbohydrate, chitin, and stored carbohydrates are in the form of glycogen
• Fungi show great diversity in morphology and habitat
• They are decomposers and parasitic
• The 'fruit' body of a fungus is only seen, while the living body is a mycelium made up of tiny filaments called hyphae

Characteristics of Fungi

• Eukaryotic, absorptive, and mostly multicellular (except for yeast)
• Heterotrophic (decomposers and parasitic)
• Mycelium (body of hyphae)
• Firm cell walls (generally of chitin)
• "Spores" as reproductive bodies
• Unique chromosomes and nuclei
• Includes molds, yeasts, rusts, and mushrooms

Types of Hyphae

• Septate hypha: multicellular, walls divided by septa
• Coenocytic hypha: continuous cytoplasm, multinucleate, no septa

Nutrition in Fungi

• Fungi absorb nutrients from the organic material in which they live
• They do not have stomachs, but digest their food before it passes through the cell wall into the hyphae
• Hyphae secrete enzymes and acids that break down organic material into simple compounds

Modes of Nutrition

• Heterotrophy: obtaining nutrients by absorbing them from the environment
• Saprophytes: feeding on dead tissues or organic waste (decomposers)
• Symbionts: mutually beneficial relationship between a fungus and another organism
• Parasites: feeding on living tissue of a host (pathogens)

Kingdom Fungi

• About 100,000 species
• Uses: medicine, food
• Ecological value: major decomposers, symbiotic relationships (N2 fixers)
• Problems: some strains are lethal, destroy library books, destroy crops

Division Chytridiomycota

• Mainly aquatic
• Some are saprobes, while others parasitize protists, plants, and animals
• Chitinous cell wall
• Flagellated zoospores
• The most primitive fungi

Phylum Zygomycota

• "Zygote fungi" (bread molds)
• Zygote = "mated" hyphal strands
• Live in soil, water
• Some are parasites
• 600 species

Characteristics of Zygomycota

• Cell walls contain chitin, chitosan, and polyglucuronic acid
• Some members typically bear multinucleate, coenocytic hyphae, without cross walls (septa)
• Importance: organic degraders/recyclers, useful in foodstuffs/fermentations, pathogens of insects and animals### Zygomycota
• The Zygomycota phylum contains approximately 1% of the described species of true Fungi (~900 species).
• Familiar representatives of Zygomycota include fast-growing molds that cause spoiling of fruits high in sugar content.
• Some Zygomycota species are considered decomposers, pathogens, or form mycorrhizal associations with plants.

Rhinocerebral Zygomycosis

• Rhinocerebral zygomycosis is a disease caused by Zygomycota organisms.
• The variety of organisms causing disease has expanded, and manifestations of disease have also evolved.

Life Cycle of Zygomycota

• The zygosporerepresents the teleomorphic (sexual; perfect form) phase of this phylum.
• The zygomycete Rhizopus can reproduce either asexually or sexually.
• Asexual stage: hyphae develop, and branches termed sporangiophores produce sporangia.
• Thin-walled sac (sporangium) is walled off at the tip and fills with cytoplasm containing multiple nuclei.
• Cytoplasmic cleavage and separation of nuclei produce sporangiospores.
• Sporangiospores germinate to repeat the asexual life cycle.

Sexual Stage

• Mating process: hyphae make physical contact and exchange chemical signals to establish that each is of a different mating type.
• Hyphal tips grow, loop back, and swell (becoming progametangia).
• Nuclei mix and fuse, and the immediate region is walled off from the rest of the hyphae (gametangium or zygosporangium formation).
• Zygosporangium becomes thick-walled to form the zygospore.
• Zygospore is dormant for a time, but then germinates to produce a sporangium containing sporangiospores.

Ascomycota

• The Ascomycota phylum is a very large group of about 32,000 named species, with more being discovered each year.
• Ascomycetes include yeasts, common molds, morels, and truffles, as well as many serious plant pathogens.
• Asexual stage: anamorph stage, characterized by vigorous asexual reproduction in most taxa by formation of conidia.
• Sexual stage: teleomorph stage, characterized by sexual reproductive cells containing meiotic products termed ascospores.
• Ascomata are the fruiting bodies, in which asci are formed.

Characteristics of Ascomycota

• Ascomycota can be distinguished by their reproductive features.
• Decomposers and pathogens of humans and animals are included in this phylum.
• Powdery mildews of crops are also Ascomycota.

Asci and Ascospores

• Asci and ascospores of Tuber and Sordaria are characterized by thin sac layers and a ring-like structure.
• Ascomycota fruiting bodies take on diverse forms, such as flask-shaped perithecia and cup-shaped apothecia.

Perithecium and Apothecium

• Perithecium: a flask-shaped fruiting body with a long neck and ostiole.
• Apothecium: a cup-shaped fruiting body with asci arranged upon the ascocarp.### Closed Structure
• The closed structure of a cleistothecium is characterized by circular asci, arranged irregularly, and spores discharging from the ascocarp by dissociation of the ascocarp cell wall.
• A diagram and photomicrograph of a cleistothecium showing asci and ascospores are provided.

Division Ascomycota

• The thallus (mycelium) consists of a highly branched network of multinucleate, septate, usually colorless hyphae.
• Many-branched conidiophores sprout on the mycelia, bearing individually conidiospores, which are the main dispersal route of the fungi and often green in color.
• Sexual reproduction involves the production of ascospores.

Phylum: Basidiomycota

• Characteristics:
  • Majority are terrestrial, although some can be found in marine or freshwater environments.
  • Oldest confirmed basidiomycete fossil is about 290 million years old.
  • Some are molds, some are yeasts, and some are dimorphic.
  • Cell wall is multilayered, consisting of chitin and glucans.
  • Production of complex fruiting structures.
  • Production of a conidial anamorph.
  • Sexual spores are basidiospores, exogenously produced on basidium.
• Classes:
  • Basidiocarp lacking and replaced by Teliospores, grouped in sori or scattered within the host tissues -- Teliomycetes.
  • Basidiocarp usually well-developed, Basidia typically organized as a hymenium -- Hymenomycetes and Gasteromycetes.

Class: Teliomycetes

• Characters:
  • Includes many economically important plant pathogens, commonly known as rusts and smuts.
  • Puccinia species produce reddish-brown color on leaf.
  • Teliospores are produced.
• Rust fungi produce up to five types of spores in their life cycle:
  • Stage 0: Spermagonia with spermatia and receptive hyphae (Pycniospores).
  • Stage I: Aecia with aeciospores.
  • Stage II: Uredia with uredospores.
  • Stage III: Telia with teleutospores.
  • Stage IV: Basidia with basidiospores.

Spores

• Pycniospores:
  • Produced in a flask-shaped structure called a pycnium.
  • Single-celled and behave as spermatia.
• Aeciospores:
  • Single-celled, produced in cup-like structures known as aecia.
  • Yellow to orange in color with a hyaline, characteristically verrucose wall.
• Uredospores:
  • Single-celled, binucleate, pedicellate, borne in naked or paraphysate sori.
  • Break through the host epidermis, commonly called uredia.
  • Brown, behave as conidia, and repeat several cycles in a season.
• Teliospores:
  • Binucleate, pedicellate or sessile, embedded in host tissue.
  • May be single-celled, bicelled, or more than 2-celled, with dark brown walls.
  • Produce basidium and basidiospores upon germination.
• Basidiospores:
  • Haploid, unicellular spores borne on sterigma.
  • Arise from cylindrical to club-shaped 2 to 4 celled basidia.