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