Chapter 12:The Eukaryotes: Fungi,

Algae, Protozoa and Helminths

Kingdom FungiThe Fungi

• Aerobic (molds and yeasts) or facultatively anaerobic (yeasts)

• Chemoheterotrophic

• Most are decomposers

• Mycology is the study of fungi

• >100,000 species

─ ~200 are pathogenic to humans/animals

Fungi vs. Bacteria

asexual

• Filamentous fungi (mostly aerobic)

─ Hyphae: cellular filaments

◦ Vegetative hyphae: responsible for obtaining nutrients

◦ Aerial hyphae: responsible for reproduction (often bear spores)

─ Mycelium: macroscopic mass of hyphae

The Fungi:Molds

Figure 12.2

The Fungi:Molds

Figure 12.1

• Reproduction

─ Fragmentation of hyphae (asexual)

─ Production of spores (sexual or asexual)

◦ Asexual spores: from hyphae of one organism; genetically identical to parent

◦ Sexual spores: from fusion of two nuclei of opposite mating strains of the same species

◦ Released spores will germinate to form a new mold

◦ Spores may be important in identification of fungal species

Figure 12.5

• Nonfilamentous, unicellular, round/oval

• Reproduce by budding or fission

• Capable of facultative anaerobic growth

─ Absence of oxygen, ferment carbohydrates into alcohol and carbon dioxide

The Fungi:Yeasts

Figure 12.3

The Fungi:Dimorphism

• Demonstrate both yeastlike and moldlike growth, depending on environmental conditions (temperature, CO2 levels, etc.)

Figure 24.17

The Fungi:Adaptations

Fungi have adapted to thrive where many bacteria can’t

• Good growth at pH 5

• Tolerant of high osmotic pressure

• Growth in the presence of low moisture

• Metabolize complex carbohydrates that most bacteria cannot

Molds are likely to spoil food that bacteria can’t

Mycoses are typically serious in immunocompromised individuals

• Systemic mycoses Deep within body

• Subcutaneous mycoses Beneath the skin

• Cutaneous mycoses Affect hair, skin, nails

• Opportunistic mycoses Caused by normal microbiota or fungi that

are left unchecked

The Fungi:Infections (mycoses)

The Fungi:Infections (mycoses)• Candidiasis: Candida albicans (Cutaneous

mycosis)

─ Constituent of normal microbiota of the genitourinary tract and mouth (relatively small population)

─ Infection frequently occurs in people treated with broad-spectrum antibacterial drugs

─ Thrush, vaginitis (yeast infections)

Figure 21.17

The Fungi:Infections (mycoses)

• Pneumocystis pneumonia: most common life-threatening infection for AIDS patients

─ Pneumocystis jiroveci

─ Opportunistic fungus

─ Systemic mycosis; uncommon before AIDS epidemic

◦ Considered to be an initial clue for AIDS

Kingdom Protista:The Protozoa

• Unicellular eukaryotes

• Found mostly in soil and water

─ Mostly aerobic

• Chemoheterotrophs

• Vegetative form is a trophozoite

─ Feeding/growing stage, typically motile

• Digestion in vacuoles, waste eliminated through plasma membrane or an anal pore

• Asexual reproduction by fission, budding, or schizogony (multiple fission)

─ Sexual reproduction by some

• Live in areas with large supply of water

• Some produce cysts in adverse conditions

─ Protective capsule

─ Survival in harsh conditions

─ Survival of parasitic species outside of host

Protozoa

• Trichomonas vaginalis

─ Parasite

─ No cyst stage

Parasitic Protozoa:Role of Cysts

Figure 12.17b

Parasitic Protozoa:Role of Cysts• Giardiasis (prolonged diarrhea)

─ Giardia lamblia attaches firmly to human intestinal wall

─ ~7% of humans are healthy carriers; shed cysts in feces

─ Most outbreaks due to contaminated water supplies

─ Diagnosis: presence of cysts in feces or the string test (to detect trophozoites in upper bowel)

Figure 12.17dFigure 25.18www.sciencedaily.com

Protozoa:Mechanisms of Motility

• Mechanisms of motility:

─ Cilia

─ Flagella

─ Pseudopods

◦ May also be used for food ingestion (phagocytosis)

Figure 12.18a

• Some species have complex life cycles

─ Multiple hosts

• Plasmodium (causes malaria)

Parasitic Protozoa:Complex Life Cycles

Plasmodium and Malaria• Malaria: 300-500 mill people worldwide are infected each

year

• Two hosts:

─ Mosquito

◦ Definitive host: harbors sexually reproducing stage

─ Human

◦ Intermediate host: harbors asexually reproducing stage

◦ Destruction of red blood cells (anemia)

◦ Release of toxins (fever/chill cycles)

◦ Alteration of RBC shape can clog tissue capillaries (kidney, liver, brain damage)

Figure 23.25

Parasitic Protozoa with Complex Life Cycles:

PlasmodiumInfected mosquito bites human; sporozoites migrate through bloodstream to liver of human

Schizogony in liver cell; merozoites are produced

Merozoites released into bloodsteam may infect new red blood cells

Merozoites are released when red blood cell ruptures; some infect new red blood cells, and some develop into male and female gametocytes

1 2

3

4

6

Asexual reproduction

Intermediate host

Merozoite develops into ring stage in red blood cell

Ringstage

Merozoites

Another mosquito bites infected human and ingests gametocytes

7

5 Ring stage grows and divides, producing merozoites

Definitive host

In mosquito’s digestive tract, gametocytes unite to form zygote

8

Male gametocyte

Female gametocyte

Zygote

Sexualreproduction

Resulting sporozoites migrate to salivary glands of mosquito

9

Sporozoites in salivary gland

Figure 12.19

Kingdom Animalia:The Helminths

• Helminths (parasitic worms)

─ Multicellular animals

─ Chemoheterotrophic

─ Complex life cycles (often several hosts)

◦ Intermediate and definitive hosts

◦Transmission usually by ingestion

─ Often produce few symptoms

Animalia

Platyhelminthes(Flatworms)

Nematodes(Roundworms)

Flukes Tapeworms

The HelminthsCharacteristics that distinguish parasitic helminths

from other free-living animals:

• May lack a digestive system (can absorb nutrients from host)

• Reduced nervous system (don’t have to search for food or respond much)

• Locomotion may be reduced or absent

• Often complex reproductive system

─ Monoecious: hermaphroditic

─ Dioecious: separate sexes

The Helminths:Flukes

• Flat, leaf-shaped

• Oral and ventral suckers hold fluke in place

• Absorb food through cuticle

Figure 12.25

The Helminths:Lung Fluke life cycle

Figure 12.26

Diagnosis

The Helminths:Tapeworms

• Intestinal parasites

─ Complete lack of digestive system

• Scolex (head) includes suckers and hooks for attachment

• Segmented

─ Proglottids: contain male and female reproductive organs

◦ When mature, they are “bags of eggs”

Figure 12.27

The Helminths:Tapeworms• Beef tapeworm (Taenia

saginata)

─ Cattle ingest proglottids

─ Larvae hatch, bore through intestinal wall and migrate to muscle (meat) and encyst (cysticerci)

─ Humans eat infected meat, and digest all parts except the scolex

─ Scolex latches on to intestinal wall and begins producing proglottids (can grow up to 6 meters!)

◦ Vague abdominal discomfort

• Diagnosis: presence of proglottids/eggs in feces

The Helminths:Roundworms

• Cylindrical, tapered at the ends

• Complete digestive system

• Motile

• Mostly dioecious

Figure 25.21

Figure 25.25

• Ascariasis (Ascaris lumbricoides)

─ Acquired by ingestion of eggs

◦ Eggs, excreted in feces, can survive in soil up to 10 yr

─ Larvae travel to lungs, where they grow

─ Adults up to 1 foot in length, inhabit small intestine

─ Diagnosis: presence of eggs in feces

The Helminths:Roundworms