Chapter 5.3 Protozoans

What does "protozoa" literally mean?

"First animal"

Why does protozoa mean “first animal“

they hunt their prey like animals and have specialized organelles resembling animal structures (mouth, digestive systems, reproductive tracts)

How many protozoan species exist and what percentage are pathogenic?

Approximately 65,000 species exist; most are harmless environmental organisms, with only a few species being true parasites or pathogens

What is unique about Kingdom Protista among eukaryotes?

They are the only group of eukaryotes that do not create tissues or organs - they remain unicellular

What are the two sub-kingdoms of Protista?

• Algae

• protozoa

Subkingdom Algae

photosynthetic

Subkingdom Protozoa

ingest other living microbes

What do Protists represent?

any unicellular or colonial organism that lacks true tissues

Which sub-kingdom of Protista is pathogenic to humans?

Only the protozoans (not the algae)

What organelles do protozoans have that are typical of eukaryotes?

All typical eukaryotic organelles EXCEPT chloroplasts

Organelles can be highly specialized into structures analogous to

• mouths

• digestive system

• reproductive tracts

• locomotive appendages

How do protozoans obtain their nutrition?

They are heterotrophic

Heterotrophic

they acquire nutrients from prey they consume, either by scavenging debris or actively hunting live bacteria/algae

What are the two main nutritional lifestyles of protozoans?

• Free-living

• Parasitic

Free Living protozoan species

• scavenge debris from dead organisms or hunt live bacteria/algae

• Scavenge dead plant or animal debris

• Graze on live cells of bacteria and algae

Parasitic Protozoan species

• feed on host fluids or destroy/ingest host tissues

• May actively feed on tissues

Pseudopods

• Also serve as feeding structures

• also called “false feet“

What is a trophozoite?

The normal, metabolically active cellular form of a protozoan that requires a constant supply of food and water for growth, metabolism, and reproduction

What is a cyst and when does it form?

A dormant, protective stage that forms when food or water is scarce; it allows the protozoan to survive adverse conditions and helps pathogenic species survive stomach acid

How does a cyst become active again?

When the cyst enters an environment with water (like the intestinal tract), enzymes activated by water digest the cyst wall and release the trophozoite inside

Why are cysts clinically significant?

They help pathogenic protozoans survive passage through the host's stomach acid, allowing them to reach the intestinal tract where they can cause infection

What are the four main groups of protozoans based on locomotion?

• Pseudopods (use pseudopodia)

• Flagellates (use flagella)

• Ciliates (use cilia)

• Sporozoans (non-motile)

Pseudopodians

• Primarily amoeba

• Use pseudopods for locomotion

• Reproduce asexually by fission

• Can encyst for protection

• Free-living

How do pseudopods move and what is an example?

They use extensions of their cell membranes called pseudopods to reach out and pull themselves through their environment; Example: Amoeba

How do flagellates move?

They use one or more flagella to propel themselves through the environment (some may also use pseudopods for enhanced motility)

How do ciliates move and what additional functions do cilia serve?

They use small, numerous cilia that whip back and forth; cilia can also enhance feeding ability and help anchor to surfaces

What is unique about sporozoans?

They cannot move because they lack the necessary locomotor appendages

Which group of protozoans has never been found to cause human infections?

Ciliates - all members are free-living and none are human pathogens (they typically affect livestock only)

Which group of protozoans is entirely parasitic?

Sporozoans

Sporozoans

• they are the only group that is entirely parasitic

• Non-motile, obligate parasites

• also called Apicomplexa

What are the two main types of protozoan reproduction?

Asexual reproduction (mitosis and multiple fission) and sexual reproduction (syngamy)

What is mitosis in protozoans?

An asexual process where a single cell creates two and only two genetically identical daughter cells per mitotic event

What is multiple fission?

An asexual process where nuclear contents replicate and divide repeatedly, creating a single cell with many nuclei, followed by rapid cytoplasmic division to create dozens or hundreds of daughter cells at once

Which type of reproduction is most common among parasitic protozoan species?

Multiple fission events

What is syngamy?

Sexual reproduction where two protozoan cells fuse to combine their genetic material into a single cell

Why must meiosis follow syngamy?

After fusion, the new cell has twice the amount of DNA it needs, so meiosis is required to reduce the DNA content back to normal levels

Which group of protozoans most often reproduces sexually?

Flagellates most often reproduce sexually by syngamy

Name the major disease-causing pseudopods and their associated diseases.

• Entamoeba histolytica → gastrointestinal infection/dysentery

• Naegleria fowleri → primary amoebic meningoencephalitis

What does the expression "don't drink the water in foreign countries" typically refer to?

Entamoeba histolytica contamination that can cause gastrointestinal infections

Name the major disease-causing flagellates and their diseases.

• Trichomonas vaginalis → reproductive tract infections

• Trypanosoma species → African sleeping sickness and Chagas disease (South American sleeping sickness)

Name the major disease-causing sporozoans and their diseases.

• Plasmodium falciparum → malaria

• Toxoplasma gondii → toxoplasmosis

According to WHO 2021, where does malaria rank among causes of death in low-income countries?

Malaria ranked as the #4 cause of death annually in low-income countries

What is the best example of a sporozoan?

Plasmodium falciparum, which causes malaria

Why are protozoan infections less common in the US?

They are more common in other parts of the world; travel to other countries increases likelihood of exposure

What is parasitology?

A sub-discipline of microbiology that focuses on studying the physiology and pathogenicity of infectious protozoans and worms

What factors are used to identify protozoans under the microscope?

• Size and shape of cell,

• type of locomotor appendage,

• distribution and number of appendages,

• ability to form cysts

• number of nuclei present

What types of specimens can be collected to diagnose protozoan infections?

Respiratory sputum, cerebrospinal fluid, fecal matter, or vaginal secretion swabs (depending on infection location)

What is an advantage of identifying protozoans compared to bacteria?

It's often possible to identify the genus by microscopic appearance alone without staining (unlike bacteria which typically require staining)

What special structures do ciliates have that other protozoans lack?

Obvious mouth-like structures and feeding organelles

Which group of protozoans can alternate between trophozoite and cyst forms?

Most groups can alternate, but some species only exist in trophozoite form and never make cysts

Which group has the most well-developed asexual and sexual stages?

Sporozoans have the most well-developed asexual and sexual stages

How do some flagellates enhance their motility beyond using flagella?

Some flagellates may also use a form of pseudopod to enhance their overall motility

Why do protozoan infections have a greater impact when contracted abroad?

Because people don't typically have to deal with these microbes at home, they lack immunity and the infections can have significantly greater health impact

Which populations are especially vulnerable to protozoan infections?

Immunocompromised patients (such as those with HIV/AIDS) are especially vulnerable

How are many protozoan diseases transmitted?

Often through contaminated food/water (cysts), insect vectors (mosquitoes, tsetse flies), or direct contact

Define heterotrophic.

Organisms that acquire nutrients by consuming other organisms (cannot make their own food)

Define multiple fission vs binary fission.

Multiple fission produces many offspring at once from a single cell; binary fission produces only 2 offspring

What is the difference between mitosis and meiosis in protozoans?

Mitosis is asexual reproduction creating identical cells; meiosis reduces DNA content by half and occurs after sexual fusion (syngamy)

Define the role of cysts in infection.

they are protective structures that allow parasites to survive stomach acid, enabling gastrointestinal infections when ingested

What makes sporozoans unique among protozoans?

They are non-motile (cannot move), entirely parasitic, and have the most well-developed sexual and asexual reproductive stages