Eukaryotic Microorganisms: Fungi, Algae, and Protozoa

Eukaryotic Microorganisms (Informal Groups)

Broadly categorized into Kingdom Fungi, Algae, and Protozoa.

Fungi

Diverse heterotrophic organisms characterized by the presence of chitin in their cell walls.

Algae

Simple autotrophs, meaning they perform photosynthesis.

Protozoa

Microscopic heterotrophs that are not classified as fungi and are always unicellular.

Kingdom Protista

Encompasses Protozoa (always unicellular) and Fungi/Algae (may be unicellular or multicellular).

Distinctions from Prokaryotes

Eukaryotes possess a true nucleus, membrane-bound organelles, can exist in haploid and/or diploid states, reproduce asexually via mitosis, and sexually via meiosis.

Mycology

The scientific field dedicated to the study of fungi.

Microscopic Fungi

Commonly include yeasts and molds.

Yeasts

Unicellular fungi that are strictly unicellular; individual cells separate following cell division.

Molds

Filamentous fungi, composed of a mass of individual thread-like structures called hyphae.

Hyphae

Individual thread-like structures that compose molds.

Mycelium

A visible, macroscopic mass of hyphae, composed of submerged (vegetative) hyphae for nutrient absorption and aerial (reproductive) hyphae for spore dispersal.

Dimorphic Fungi

Fungi that possess the ability to grow either as single yeast cells or as multicellular mycelia, often in response to environmental cues such as temperature (e.g., *Candida albicans*, *Histoplasma capsulatum*).

Chitin

The primary component of fungal cell walls.

Ergosterol

Typically found in fungal cell membranes.

Exoenzymes

Secreted by fungi to degrade larger polymeric molecules into smaller, absorbable units.

Decomposers (Fungi)

Fungi are crucial decomposers in ecosystems, breaking down complex organic matter like cellulose and lignin and facilitating the release of CO\_2 and nitrogen compounds back into soils.

Saprobes

Fungi that obtain nutrients predominantly from dead or decaying organic matter.

Fungal Parasites

Some fungi can act as parasites of living tissues, though none are obligately parasitic. Few cause human infections; plant infections are common.

Reproduction in Yeasts

Primarily reproduce asexually by mitosis or budding.

Septate Hyphae

Hyphae possessing cross-walls (septa) that divide them into distinct cell-like compartments.

Non-septate (Coenocytic) Hyphae

Hyphae lacking cross-walls, appearing as continuous, multinucleated cytoplasm.

Spores (Fungi)

Produced by aerial hyphae, serving as reproductive and dispersal units. Asexual spores are produced via mitosis; sexual spores via meiosis and fertilization.

Eumycota (Major Groups)

Broadly classified into 4 major groups: Chytridiomycota, Ascomycota, Zygomycota, and Basidiomycota.

Chytridiomycota

Mostly aquatic fungi, with some species found inhabiting the mammalian gut.

Ascomycota

Includes the majority of yeasts, as well as macroscopic edible fungi such as truffles and morels.

Zygomycota

Contains coenocytic molds, an example being *Rhizopus*.

Basidiomycota

Most famously known for mushrooms, but also comprises some yeasts, smuts, and rusts.

Deuteromycota

Historically a classification for fungi (imperfect fungi) where a sexual stage had not been observed.