Chapter 5 - Fungi, Algae, Protozoa and Multicellular Parasites



Chapter 5 - Fungi, Algae, Protozoa and Multicellular Parasites

I. Fungi – mycology = branch of microbiology that studies fungus

A. Importance

1. human fungal infections - nosocomial; opportunistic; numbers increasing

2. plant pathogens - >$1 billion in damage /yr.

3. Beneficial - decomposers; mycorrhizae; foods; alcohol; drugs

B. Characteristics of Fungi

1. vegetative structures - molds or fleshy fungus

a. hyphae - vegetative ( feeding) or aerial (for reproduction)

b. septa; septate hyphae; aseptate (coenocytic hyphae)

c. mycelium - groups of hyphae (macroscopic)

2. vegetative structures - yeasts

a. nonfilamentous; unicellular; oval to round

b. divide by fission or budding

c. budding yeasts - buds from parent; pseudohyphae

d. ferment carbohydrates ( ethanol + CO2 ; beer, wine; baking

3. Dimorphic fungi - molds at 250C; yeasts at 370C

3. Life cycle

a. reproduction - asexual ( by hyphae or spores) ; sexual ( by sexual spores)

b. fungal spores - differ from bacterial endospore ; true reproductive spore; limited resistance to heat & drying

c. asexual spores formed by hyphae of one organism - genetically identical to parent;

conidiospores (conidia) – asexual spores , not enclosed in a sac

sporangiospores - asexual spores enclosed in a sac

sexual spores

2 haploid cells - nuclei fuse ( form diploid zygote

zygospores, ascospores, basiospores

5. Nutritional adaptations

a. chemoheterotrophs; absorb nutrients

b. Tolerate acidic pH ( about pH 5)

b. molds - almost all aerobic; yeasts - facultative anaerobes ;fermenters

c. resistant to high osmotic pressure ( can tolerate high sugar or salt environments)

d. can grow with very low moisture

e. require less nitrogen for growth than bacteria

f. can metabolize complex carbohydrates ( e.g. wood)

C. Four Medically Important divisions

1. Zygomycetes

a. sexual reproduction ( zygospores) or asexual reproduction (sporangiospores)

b. aseptate hyphae

c. e.g. Rhizopus - black bread mold

1. Ascomycota ( sac fungi)

a. asexual spores ( conidiospores; conidia)

b. sexual spores ( ascospores produced in a sac called an ascus)

c. e.g., Penicillium, Aspergillus

d. molds with septate hyphae ; some yeasts

1. Basidiomycota ( club fungi)

a. asexual spores - conidiospores

b. sexual spores - basidiospores formed on a pedestal ( basidium)

c. e.g., Cryptococcus; mushrooms

1. Deuteromycota

a. asexual reproduction only; no sexual stage

b. septate hyphae

c. contain most of the human pathogens

D. Fungal diseases ( mycosis= a fungal disease)

1. Superficial mycoses – grow on surface cells or hairshafts

2. Cutaneous mycoses - affect epidermis, skin, and nails; dermatophytes

3. Subcutaneous mycoses – fungi can invade beneath the skin; infects the subcutaneous tissue, connective tissue; cause cellulites; often introduced by puncture wounds

4. Systemic mycoses - occur deep within the body; can affect any tissues or major organs ; e.g., histoplasmosis; coccidiomycosis

5. Opportunistic pathogens; The organism oes not cause disease in a healthy host, but is pathogenic in a compromised host ( one who is weakened by an underlying condition) ; Rhizopus, Mucor, Aspergillus, yeast

6. Yeast infections – Most human yeast infections are caused by Candida albicans

7. Fungal Toxins – mycotoxins – usually potent; only minute quantities needed to cause damage to cells.

E. Economic Effects

1. Saccharomyces cerevesiae (“Baker’s yeast” – bread) (“Brewer’s yeast” - beer & wine)

2. Saccharomyces cerevesiae - genetic engineering - produce human proteins, vaccines

3. protein supplements for humans and livestock

4. producers of taxol (anti-cancer drug)

5. biological control of pests (e.g. gypsy moths)

6. used to prevent fungal growth on harvested fruits

7. mold spoilage of harvested fruits & vegetables ( 25-50% of annual harvest is lost to mold damage)

8. plant pathogens; potato blight; chestnut tree blight; Dutch elm disease

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download