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
4. 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)
c. molds - almost all aerobic; yeasts - facultative anaerobes ;fermenters
d. resistant to high osmotic pressure ( can tolerate high sugar or salt
environments)
e. can grow with very low moisture
f. require less nitrogen for growth than bacteria
g. 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