Fungi, algae, protozoa and multicellular parasites

Fungi

Medically, economically and environmentally important

Structures

Molds and fleshy fungi Thallus (the body) is composed of hyphae which are long filaments of cells. This can be immense- the hyphae of a single fungus identified in Michigan extends across 40 acres and estimated to weigh over 10 tons. The hyphae may have cross walls called septa and are called septate hyphae or may not have cross walls and these are called coenocytic hyphae. Hyphae grow at the tip. Under suitable environmental conditions, the hyphae may grow to form mycelium which is visible.

Yeasts are nonfilamentous, unicellular fungi. Found in nature as white powdery coating on fruits and leaves. Divide either by fission - so called fission yeast or by budding - so called budding yeast. Yeasts are facultative anaerobes - aerobically they respire and anaerobically they ferment making things like ethanol. Some pathogenic fungi are dimorphic fungi that may either grow like a mold with hyphae or a yeast that reproduces by budding. This is temperature dependent.

Life cycle

Filamentous fungi may reproduce asexually or sexually. Fragments of hyphae will produce more hyphae. Spores may be formed sexually or asexually. Asexual spores are formed by mitosis from the hyphae of a single organism. The spores produce individuals that are genetically identical to the parent. Sexual spores result from the fusion of two opposite mating types.

Spores are important in the identification of fungi.

Asexual spores include conidiospores, chlamydospores, and sporangiospores. Sexual spores form from haploid nuclei fusing to form a diploid zygote. The diploid zygote goes through meiosis to produce haploid nuclei (sexual spores).

Nutritional adaptations

chemoheterotrophs

grow better than bacteria at low pH (~5.0)

more resistant to high osmotic pressure - can grow in sugary or salty solutions

can grow on substrates with low moisture content

require less nitrogen than bacteria for a given amout of biomass

metabolize complex carbohydrates such as lignin - bacteria cannot

Medically important divisions of fungi

Deutermoycota

do not produce sexual spores; produce asexual spores. Considered the holding category of the fungi until sexual spores are observed. Pneumocystis is an opportunistic pathogen in individuals who are immunocompromised.

Zygomycota

saprophytic molds that have coenocytic hyphae. Form zygospores which are large spores. Example includes Rhizopus nigricans which is the common black bread mold.

Ascomycota

Referred to as the sac fungi because their sexual spores are contained in sacs called an ascus. An example is Aspergillus.

Basidiomycota

Referred to as the club fungi. This group includes the mushrooms. Basidiospores are produced sexually. The basidium where the basidiospores form has a club like shape.

Fungal diseases

Fungal infection is called a mycosis. There are systemic mycoses - deep infections, subcutaneous mycoses - beneath the skin, cutaneous mycoses - infect the hair, epidermis, and nails, superficial mycoses - along hair shafts or surface epidermal cells and opportunistic mycoses - become pathogenic.

Economic effects of fungi

Beneficial aspects:

Negative aspects

Algae

Generally aquatic though they are found in the hair of both the South American Sloth and the Polar Bear. Some are unicellular, others are filamentous and still others have plant like bodies called thalli.

Structures

Multicelluar algae

Body called thallus. Thallus may consist of holdfasts which anchor seaweed for example, stem-like hollow stipes and leaf-like blades. The cells covering the thallus are photosynthetic. They lack conductive tissue like the xylem and phloem of vascular plants.

Life cycle

They can reproduce asexually by fragmentation. Sexual reproduction occurs in some algae.

Nutrition

They are all photoautotrophs found in the photic zone of bodies of water. Chlorophyll a and accessory pigments are responsible for the different colors of algae.

Divisions of algae

Lichens

combination of green alga or blue green bacteria and a fungus. Form a mutualistic relationship where both partners benefit. Fungus provides against dessication and provides a holdfast and the alga provides upwards to 60% of its photosynthate to the fungus. Frequently one of the first colonizing organisms especially on newly exposed rocks. They excrete acids to make nutrients available to them from the rock.

Three morphological types of lichen: (See figure 12.14 and identify the three types)

Lichens used for dyes in parts of the world, some produce antimicrobials, some cause allergic responses in humans on contact.

Protozoa

Reproduce

reproduce in a number of different ways:

Asexually

Sexually

Nutrition

aerobic heterotrophs usually though there are intestinal protozoa that are anaerobes.

Divisions