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Chapter 12
The Eukaryotes: Fungi, Algae, Protozoa, and Helminths
Part 1
Fungi, Algae, Protozoa, and Helminths
Fungi
• Mycology: the study of fungi– rRNA sequencing causing many reclassification
• Eukaryotic (unicellular, filamentious, fleshy)
• Aerobic or facultatively anaerobic
• Chemoheterotrophic
• Most are decomposers (important in the food chain); absorb nutrients instead of ingestion– decompose dead plant matter (organic molecules
to inorganic molecules) & recycle vital elements
Fungi• Few are plant and human pathogens • Incidence of serious fungal infections have
been rising – Nosocomial infections and in people who are
immunocompromised
• Beneficial– Recycling of nutrients in the environment– Symbiotic fungi (mycorrhizae) help plants roots
absorb minerals and water from the soil– Serve as food; used to produce foods and drugs
for humans
Fungi
Table 12.2
Characteristics of Fungi
• Fungal structures are used for identification in a clinical laboratory– Yeast identification based on biochemical tests– Multicellular fungi based on physical appearance:
1) colony characteristics, 2) type of hyphae, and 3) reproductive spores (asexual spores for clinical ID & sexual spores for phyla)
• Fungal colonies (vegetative structures) are composed of the cells involved in catabolism and growth
Molds and fleshy fungi
Fig. 12.1
• The fungal thallus (body) consists of hyphae; a mass of hyphae is a mycelium.– Hypha (pl. hyphae): a long filament of cells in
fungi– Septate hyphae: hyphae with cross-walls (septa)– Coenocytic hyphae: hyphae with no septa
– Vegetative hypha: the portion of a hypha that obtains nutrients
– Reproductive (aerial) hypha: the portion of a hypha concerned with reproduction
– Aerial hyphae bear reproductive spores
Molds and fleshy fungi
Figure 12.2
Yeasts
• Unicellular fungi; usually spherical or oval shape; usually reproduce by budding
• Capable of facultative anaerobic growth– Fermentation used in brewing, wine-making, and
baking
• Pseudohypha: A short chain of fungal cells that results from the lack of separation of daughter cells after budding
• Yeast cells grown on a solid medium resemble bacterial colonies
• Fission yeasts divide symmetrically (e.g. Saccharomyces)
• Budding yeasts divide asymmetrically
Yeasts
Figure 12.3
• Pathogenic dimorphic fungi are yeastlike at 37°C and moldlike at 25°C– Moldlike form
produce aerial and vegetative hyphae
– Yeastlike form reproduce by budding
Dimorphic fungi
Figure 12.4
Life cycle
Fig. 12.1
• Filamentous fungi can reproduce asexually by fragmentation of their hyphae
• Sexual and asexual reproduction through formation of spores (formed from aerial hyphae)
Life cycle• Asexual spores: formed by the hyphae of
one organism through mitosis– Gives rise to a new mold that is genetically
identical to the parent
• Sexual spores: result from the fusion of nuclei from 2 opposite mating strains of the same species of fungus– Gives rise to a new mold that has genetic
characteristics of both parental strains– Usually produced in response to changes in
environment
• Sporangiosphore– form within a sac called
sporangium at the end of a sporangiophore (aerial hypha), e.g. Rhizopus
• Chlamydospore– a thick-walled spore
formed by rounding and enlargement within a hyphal segment e.g. Candina albicans (yeast)
Asexual spores
Figure 12.5
Asexual spores• Conidiospore (conidium)
– a unicellular or multicellular spore that is not enclosed in a sac; produced in a chain at the end of a conidiophore (aerial hypha), e.g. Aspergillus
– Arthrospore: formed by the fragmentation of a septate hypha into single, slightly thickened cells, e.g. Coccidioides immitis
– Blastoconidium: buds coming off the parent cell, e.g. C. albicans (yeast) and Cryptotoccus
Conidiospores
Figure 12.5
• Results from sexual reproduction
• Three phases– Plasmogamy Haploid donor cell nucleus
(+) penetrates cytoplasm of recipient cell (–)
– Karyogamy + and – nuclei fuse– Meiosis Diploid nucleus produces
haploid nuclei (sexual spores)
• In laboratory setting, most fungi exhibit only asexual spores (used for clinical identification)
Sexual spores
• Zygospore Fusion of haploid cells produces one zygospore e.g. Rhizopus
Sexual spores
Figure 12.6
• Ascospore Formed in a sac (ascus), e.g. Penicillium
Sexual spores
Figure 12.7
• Basidiospore Formed externally on a pedestal
(basidium), e.g. mushrooms
Sexual spores
Figure 12.8
Nutritional adaptations
• Fungi adapted to environments that would be hostile to bacteria– Usually grow better in acidic environment (pH
of about 5) & require less nitrogen for growth– Aerobic (molds) or facultative anaerobes
(yeasts)– More resistant to osmotic pressure (can grow in
relatively high sugar or salt concentration)– Can grow on a very low moisture surface– Capable of metabolizing complex carbohydrates
(e.g. lignin)
Medically Important Phyla of Fungi
• Not all fungi cause disease– many are found as contaminants in foods and in as
contaminants on bacterial cultures (laboratory)
• Four phyla: Zygomycota, Ascomycota, & Basidiomycota (these are telomorphs); and Anamorphs (Deuteromycota)– Telomorphs: produce both sexual and asexual
spores; the sexual stage in the life cycle of a fungus– anamorphs: Ascomycete fungi that have lost the
ability to reproduce sexually; the asexual stage of a fungus (asexual spores only)
Medically Important Phyla of Fungi
• Zygomycota (conjugation fungi)– Saprophytic (obtain nutrients from dead organic
matter) molds with coenocytic hyphae– Asexual spore = sporangiospores; sexual spores
= zygospores– e.g. Rhizopus & Mucor (Opportunistic, systemic
mycoses) Rhizopus nigricans (common
bread mold)
Zygomycete Life Cycle
Figure 12.6
Medically Important Phyla of Fungi
• Ascomycota (sac fungi)– molds with septate hyphae and some yeasts– Sexual spores = ascospore; and frequently asexual
spores = conidiospores– e.g. Aspergillus (opportunistic, systemic mycosis)
Blastomyces dermatitidis, Histoplasma capsulatum (systemic
mycoses) Microsporum, Trichophyton (cutaneous mycoses)
Ascomycete Life Cycle
Figure 12.7
• Basidiomycota (club fungi, mushrooms)– Molds with septate hyphae – Sexual spores = basidiospores; and sometimes
asexual spores = conidiospores – Cryptococcus neoformans (systematic
mycosis)
Medically Important Phyla of Fungi
Basidiomycete Life Cycle
Figure 12.8
Anamorphs• Anamorphic fungi:
– Produce asexual spores only; historically fungi whose sexual cycle had not been observed were called Deuteromycota
– rRNA sequencing places most in Ascomycota, a few are Basidiomycota
– e.g. Penicillium Sporothrix (subcutaneous mycosis)
Stachybotrys, Coccidioides, Pneumocystis (systemic mycoses)
Candida albicans (Cutaneous mycoses)
• Tend to be chronic (long-lasting) infections due to slow growth of fungi & hard to treat– Drugs that will affect fungal cells (eukaryotes) also
affect animal cells (also eukaryotes)
• Systemic mycoses: deep within body– Usually caused by fungi living in soil
• Subcutaneous mycoses: beneath the skin– Usually caused by saprophytic fungi living in soil
and on vegetation
Fungal Diseases (mycoses)
• Cutaneous mycoses: affect hair, skin, nails– Usually caused by fungi living in soil, on animals
or humans (can be transmitted from human to human or from animal to human)
• Superficial mycoses: localized, e.g., hair shafts, and surface epidermal cells
– Prevalent in tropical climates
Fungal Diseases (mycoses)
• Opportunistic mycoses: caused by normal microbiota or fungi that are normally
harmless – infect immunocompromised host; patients on
broad-spectrum antibiotics; or people who is seriously debilitated or traumatized
Gypsy moth controlEntomorphaga
Ceratocystis ulm (Dutch elm disease)
Taxol productionTaxomyces
Cryphonectria parasitica (chestnut blight)
Cellulose used for juices and fabric
Trichoderma
Food spoilage
Negative Effects
Bread, wine, beerSaccharomyces
Positive EffectsFungi
Economic Effects of Fungi
• Used in biotechnology, biological pest controls vs. undesirable effects
• Mutualistic combination of an alga (or cyanobacterium) & fungus– Classified according to the fungal partner (most
often an ascomycete)– Mutualism: a type of symbiosis in which both
organisms or populations are benefited
• Alga produces and secretes carbohydrates (via photosynthesis), fungus provides holdfast (enclose alga)
• Some of the slowest growing organisms on Earth
Lichens
Lichens
Figure 12.10
Lichens
• Often the first life forms to colonize newly exposed soil or rock– Colonize habitats that are unsuitable for either
the alga or the fungus alone
• Grouped into 3 morphologic categories– Crustose, foliose, and fruiticose
• Used as dyes for clothing, an antimicrobial agent, the dye in litmus paper; cause allergic contact dermatitis