Ciliates and flagellates

General Features of ciliates

• Covered in cilia (hair-like organelles).

• Most structurally developed protozoans.

• Specialized feeding and excretion structures:

  • Cytostome (mouth)

  • Cytoproct (anus)

• Contain two types of nuclei:

  • Macronucleus – controls everyday functions.

  • Micronuclei – involved in reproduction

cilia

• Based on microtubules:

  • Motile cilia: 9+2 structure + dynein motor protein.

  • Non-motile (primary) cilium: 9+0, no dynein (seen in most human cells).

• Functions:

  • Movement (back-and-forth motion).

  • Feeding: direct prey to the cytostome using membranelles (stiffer cilia).

  • Some cilia fuse to form cirri for crawling.

  • Specialized for filter feeding.

Exception – Suctorian Ciliates

• Sessile, lack motile cilia in adult form.

• Numerous microtubule tentacles, each ending in a cytostome.

• Use extrusomes to secrete toxins.

• Kill prey externally, then suck out contents.

• Exhibit raptorial feeding.

Mixotrophic Ciliates

• Acquire photoautotrophy externally (do not make their own plastids).

• Obtain energy by feeding and photosynthesis.

Reproduction

Asexual:

• Binary fission (transverse), involves mitosis.

Sexual:

• Conjugation

  • Involves both meiosis and mitosis.

  • Exchange of micronuclei.

  • Creates genetic variation.

Anaerobic Ciliates (“Sulphur Ciliates”)

• Contain:

  • Hydrogenosomes (convert pyruvate → H₂, acetate, CO₂)

  • Methanogenic Archaea (convert products into methane)

general features of flagellates

• Possess 1–8 flagella (rarely 8).

• Flagellum has 9+2 structure.

• Motion is not back-and-forth like cilia.

• Reproduction via longitudinal binary fission (mitosis).

• Usually have a macronucleus only.

• Mostly aerobic.

• Nutritional modes:

  • Heterotrophy

  • Photoautotrophy

  • Mixotrophy

HETEROTROPHIC FLAGELLATES ("Zooflagellates")

• Aerobic.

• Feed on pre-formed organic carbon.

• Digest food into CO₂.

• Use flagella for both movement and prey capture.

Flagella Types of heterotrophic flagellates

• Naked flagellum: propels forward.

• Hispid flagellum: propels backward.

Feeding Methods of heterotrophic flagellates

Raptorial Feeding

• Hispid flagellum: more efficient, prey drawn to base and captured with pseudopodia.

• Naked flagellum: less efficient prey contact.

Enhanced Capture (Naked Flagellum)

• Use tentacle collar (microvilli).

• Contractile (contain actin).

• Filter-feeding based on prey size.

CHOANOFLAGELLATES

• Only group with a collar of tentacles.

• Always possess a single naked flagellum.

• Attach to surfaces.

• Closest protist relatives to animals.

PHOTOAUTOTROPHIC FLAGELLATES ("Phytoflagellates")

• Contain their own plastids (green or golden).

• Perform photosynthesis:

  • CO₂ → glucose (organic carbon).

• All are aerobic.

• Use flagellar motion to move toward light/nutrients.

Photoreception

Use an eyespot (stigma):

• Contains carotenoid globules.

• Acts as a shading device to help photoreceptor detect light direction.

Dinoflagellates

• Unique in having a second flagellum around the cell's "waist".

• Causes spinning motion.

MIXOTROPHIC FLAGELLATES

• Phytoflagellates that can also ingest prey.

• Constitutive mixotrophs:

  • Have their own plastids (do not rely on ingestion to photosynthesize).

  • All are aerobic.

• Use:

  • Raptorial feeding

  • Flagellar movement for prey capture and motility.

• Feeding preference depends on:

  • Genus

  • Light climate

• May be:

  • Solitary cells

  • Colonial

AMOEBAE Characteristics

• One macronucleus → Asexual reproduction

• Most are aerobic and heterotrophic

• Move via cytoplasmic streaming

• Produce pseudopodia for movement and feeding

Naked Amoebae

• E.g. Amoeba proteus

• Blob-like with no shell

• Trophozoites = active feeding form

• Cysts = dormant

• Floating forms = dispersal (stiff pseudopodia)

• -       Move by cytoplasmic streaming

  -       Produce pseudopodia on surfaces – 2 pseudopodia trap ciliate and join to form phagosome and digest

  -       Feed by direct interception of prey

  -       Raptorial feeding

  No specific location for ingestion

Shelled Amoebae (Testate)

• Live inside protective test - predator protection

• Project pseudopodia externally

• Feed via raptorial or diffusion feeding

• Produce cysts

Foraminiferans

• Marine habitat

• CaCO3 test type

• diffusion (axopodia) feeding

Radiolarians

• marine habitat

• silica test type

• diffusion feeding

Heliozoans

• freshwater habitat

• silica test type

• diffusion feeding

Positive ecological role impacts

• Base of microbial food chains

• Regulate bacterial populations

• Key in nutrient cycling

• Microbial loop:

  1. Photoautotrophs → CO₂ fixation → sugars

  2. Bacteria consume sugars

  3. Protists eat bacteria + photoautotrophs

Result: Bacteria stay in log phase, constantly active and dividing

Negative ecological role impacts

• Amoebae host bacterial pathogens

• Serve as reservoirs for pathogen evolution

Gut infections caused by protists

Flagellates e.g. Giardia lamblia

 Dysentery

•        Reservoir: Water and animals/humans

 Transport:Contaminated water, Faecal-oral route

Eye infection caused by protists

•       Amoebae belonging to genus Acanthamoeba

•        Causes Keratitis

•        Reservoir: Water

•        Transport: Dirty contact lenses

Brain infection caused by protists

One amoeba – Naegleria fowleri

 Primary Amoebic Meningoencephalitis (PAM)

 Reservoir: Warm water

 Transmission: Flagellate swims up nose

STD caused by protists

•       One flagellate – Trichomonas vaginalis

•        Trichomoniasis

•       Reservoir: Humans

Blood/tissue infection caused by protists

•       Flagellates e.g. Leishmania mexicana

•        Leishmaniasis

•        Reservoir: Dogs

•        Transmission: Sand fly (Vector)