Protozoa

1. Protozoa Background
Information
 Domain Eukarya
– Membrane bound
organelles, including nucleus
 Many kingdoms, 40+,
depending on what
classification scheme is
used
 Classification is always
changing
 Protozoa are animal-like
protists

2.  Primitive
– Single celled
– Colonial
 Gave rise to modern day
plants and animals
 Diversity is the rule in
every aspect
– Feeding / energetics
– Life cycles
– Reproduction
– Physiology /
osmoregulation
– Locomotion
– Morphology

3. Protozoan Diversity

4. Review of the Eukaryotic Cell
 Protists lack cellular specialization (with few exceptions)
 Individual organelles carry out all physiological processes

5.  Cell membrane
– Barrier to the outside environment
– Selective passage of molecules
– Plays a role in endo / exocytosis
 Cytoplasm
– Ectoplasm – outer, stiff, portion
– Endoplasm – inner, fluid, portion
 Internal membrane system
– Consists of endoplasmic reticulum (ER), Golgi
bodies, and lysosomes
– Compartmentalizes the cell

6. The Cytoskeleton
 Main types
– Microfilaments
(made of Actin)
– Microtubules
 Functions
– Maintain cell shape
– Locomotion – cilia,
flagella, and
pseudopodia
– Cell division
– Transport vesicles
around cell

7. Cilia
 Numerous, short
projections that beat in an
oar-like fashion to produce
movement
 Consists of microtubule
core (axoneme) enclosed
in cell membrane
– Ring of 9 doublets, plus two
singlets, centrally located
– (9x2)+2 pattern
 Anchored by a basal body
(9x3 pattern)

8. Flagella
 Far fewer than cilia,
but structurally
identical
 Long
 Undulate in a whip-
like fashion to produce
movement
 Both cilia and flagella
require ATP to move

9. Pseudopodia
 Used for locomotion, food capture, and endocytosis
 Actin disassembly results in a conversion of ectoplasm to
endoplasm

10. Protozoan Physiology
 Same rules apply in single celled organisms as do
in metazoans
 In fact, environmental effects may be more
pronounced
– Ectothermic
– Large SA : Vol
 Important considerations
– Feeding and nutrition
– Enzyme function
– Osmoregulation
– Reproduction

11. Feeding and Nutrition
 Heterotrophs
 Photoautotrophs
 Mixotrophs
– Can switch between
heterotrophy and
autotrophy, depending
on conditions
 Endosymbiotic theory
explains how energy
producing organelles
evolved

12.  Nutrition occurs in
four phases:
– Ingestion
– Digestion –mechanical
and/or chemical
– Absorption
– Elimination
 Digestion typically
intracellular. Food is
phagocytized and a
food vacuole is
created. Digestive
enzymes are dumped
into vacuole

13. Enzyme Function
 Protein form equals
function
 Enzymes are subject
to denaturation under
the following
conditions:
– Extreme pH
– Extreme temperature
(especially high
temperatures)
– Extreme salinity. For
this reason,
osmoregulation is
important

14. Osmoregulation
 Many protists posses a specialized
organelle known as a contractile vacuole
 A collection of tubules known as the
spongiome, collect ions from the
cytoplasm and deliver them to the
contractile vacuole proper
 The vacuole contracts and its contents
are extruded

15. Reproduction
 All species reproduce
asexually (clonally)
– Fission – splitting of
parent that results in two
or multiple individuals
– Budding – portion of
parent splits off to form
new individual
 No recombination
Budding Hydra (NOT a Protozoan)

16.  Though less common
some species can
even reproduce
sexually
 Conjugation
– two individuals fuse
– dissolve portions of
their cell membranes
– exchange genetic
material
 Recombination is the
result

17. Asexual vs. Sexual
 Advantages to clonal reproduction
– Allows reproduction in the absence of a mate. Good for
isolated species
– Allows offspring to be reproduced quickly; no energy is
lost to gamete production, fertilization, or development
– Perpetuates identical genotypes; beneficial if already
well adapted to that environment
 Disadvantage
– Limited genetic possibilities. Constricts the gene pool
and species could die out when the environment
changes

18.  Advantages to sexual reproduction
– Increases genetic variability via crossing
over, independent assortment of
chromosomes, and random fertilization
– Result may be better environmental
adaptability for certain individuals, and the
species as a whole
 Disadvantage
– Finding mates in isolated or sessile species

19. Encystment
 Water is pumped out and organism
forms capsule around itself
 Benefit is the organism can survive
harsh environmental conditions for
years
– Desiccation resistant
– Does not require food
– Wind dispersal

20. Protozoa
 Name means “first
animals”
 215,000 described
species. Equal to the
number of described
vascular plants
 10 times more diverse
than bacteria and
viruses

21. Protozoan Ecology
 Very important ecologically
 Many are photoautotrophs, and make up 40% of
all primary productivity
 Many make up a large component of plankton
communities
 25% of the described species live as symbionts.
Many of these are parasitic
 Many are important nutrient cyclers

22. Form and Function
 Protozoan body was is
known as a pellicle
 Pellicle is composed of
the cell membrane
and cytoskeleton:
– Microfilaments (Actin)
– Microtubules
– Vesicles such as alveoli
– Any combination of the
above

23. Phylum Euglenozoa
 Two main classes
– Euglenoidea
– Kinetoplastida
 Both are flagellates
 Both reproduce
asexually
 Both are solitary

24. Class Euglenoidea
 1000 species
 Elongate
 Free-living
 Solitary
 Reproduction is
clonal, and
occurs via
longitudinal
binary fission

25.  Posses a contractile vacuole
 Two flagella, one long, one short
 Posses a pigmented eyespot that shades the
photosensitive paraflagellar body
 Heterotrophic, photoautotrophic, or mixotrophic
 Photosynthetic species rotate on their
longitudinal access as they swim toward the light
 Can produce a starch-like carbohydrate
– Known as paramylon
– Produced in the pyrenoids of their chloroplasts
– Stored as granules in cytoplasm

26. Class Kinetoplastida
 600 species
 Reproduce asexually
 Posses one or two flagella
 Most are parasitic
 All posses a conspicuous
mass of DNA, known as a
kinetoplast, located in
one large mitochondrion

27.  Link between
kinetoplast and
parasitic lifestyle of
most species
– Kinetoplast codes for
mitochondrial
morphogenesis
– Parasites alternate
between aerobic and
anaerobic host
environments
 Trypanosoma is a gut
parasite of insects and
blood parasite of
vertebrates
– Chagas’s disease
– African sleeping sickness
Tsetse Fly Distribution

28.  Trypanosoma possesses one large
flagellum that joins an undulating
membrane, which runs the length of
the organism
 The pellicle’s protein composition
(antigens) is controlled by roughly
1000 genes (40% of the genome)
– Thus, the parasite is able to effectively
elude the host’s immune system

29. Phylum Chlorophyta
 Green algae
 Posses chloroplasts
with chlorophyll a and
b (same as plants)
 Can synthesize and
store starch
 Marine and freshwater
species

30.  Some genera are non-motile and
filamentous, such as Spirogyra
 Others such as Volvox are flagellated,
motile, and colonial
 In Volvox, up to 6000 individual cells may
make up a hollow spherical colony
 Individual cells are connected by
cytoplasmic bridges

31.  There is some cellular differentiation in
Volvox
– Non-flagellated gonidia (reproductive cells) can
reproduce sexually or asexually
 During asexual reproduction:
– Gonidium undergoes several rounds of fission
– Inverted (flagella pointing in) daughter colony
is created
– Flagella later point out
– Daughter colony bursts out of the parent
colony

32.  Volvox is closely related to plants, but also
provides insight to the evolution of
animals
– Blastocysts look almost identical

33. Phylum Choanoflagellata
 600 species
 Marine and freshwater
 Tiny - 10µm
 Solitary or colonial
 Free-living or sessile
 Stalked, spherical, or
occurring in sheets

34.  Not surprising that they are
closely related to animals
– Closely resemble collar cells of
sponges
 One large flagellum w/ base
surrounded by a collar of
microvilli
 Flagellum beats and collar
traps bacteria and organic
molecules
 Particles ingested by
phagocytosis
 Intracellular digestion

35. Phylum Retortamonada
 Often live in anoxic
environments
– Many living in the guts of
insects and vertebrates
– Mitochondria typically
absent, as a result of this
– Thus, adapted for
surviving on glycolysis
 Giardia lamblia posses four
flagella
 Giardia is often contracted
by drinking from mountain
streams. Symptoms are
often referred to as
“beaver fever.”

36. Phylum Axostylata
 Another heterotrophic
flagellate, closely related
to the members of
Phylum Retortamonada
 Trichomonas vaginalis is
the most famous
representative
 Small parasite with four
flagella that infects the
urogenital tract of
humans
– Can be transmitted
sexually

37. Phylum Alveolata
 Consists of three subphyla:
– Dinoflagellata
– Ciliophora
– Apicomplexa
 Have similar rDNA sequences
 Posses alveoli, sacs, deep to the cell
membrane

38. Subphylum Dinoflagellata
 Dinoflagellates
 4000 marine and
freshwater species
 Posses chloroplasts
– Important 1° producers
– Red-brown to gold-brown
in color, due to
photosynthetic pigments
– Chloroplasts acquired
through endosymbiosis
 Contribute to planktonic
bioluminescence

39.  Some are endoparasites of protozoa,
crustaceans, and fish
 Certain genera responsible for “red tides.”
– May result in massive die-offs of shellfish and fish
– Harms animals who eat contaminated organisms

40.  Posses a sulcus
and two flagella
 Have a skeleton
known as a theca
(test or lorica)
 Reproduce via
binary fission, or
may encyst

41. Subphylum Ciliophora
 8000 described ciliates
 Sophisticated protozoans
 Have some degree of anterior – posterior
polarity
 Most are motile and solitary
 Many posses specialized ciliature
– Somatic cilia
– Oral cilia

42.  Function of alveoli is to
store Ca2+
 Release of Ca2+ causes
changes in ciliary beat,
and discharge of
extrusomes
– Trichocysts – long shafts
that are thought to defend
against predators
– Toxicysts – longs shafts
with toxin that are used for
prey capture
– Mucocysts – release mucus
and creates sticky surface
for prey capture or
protective cysts

43.  Paramecium changes
directions upon
colliding with
something solid
– Known as avoidance
reaction
– Result of Ca2+ and K+
release from alveoli
– Depolarization, similar
to an action potential
 Two very interesting
sessile genera,
Vorticella and Stentor

44.  Vorticella
– Colonial
– Each cell possesses
a long stalk with a
spasmoneme (spiral
fiber)
– Contracts to
withdraw from
predators
 Stentor is a similar
genus

45.  Ciliates have two types of nuclei
– Macronucleus – genes are actively transcribed
– Micronucleus – master copy of genome; inactive except
during cell division
 Shapes and numbers of these nuclei varies across
genera
– Bean shaped in Paramecium
– String of beads in Stentor

46.  Another group of
alveolates
 The sporozoans, form
spores
 Mostly parasitic
 Posses an apical
complex
– Attaches to or
penetrates host cell
– Cone contains digestive
enzymes
Subphylum Apicomplexa

47.  Four species of Plasmodium that cause malaria
– #1 human parasite
– 300 million worldwide infected each year
– 1% die each year
– Anopheles mosquito is the vector
 Complex life cycle
– Sporozoite – motile, infective stage possessing apical complex
– Merozoite – motile, reinfective stage, also has apical complex
– Gametocytes – reproductive stage. Usually, male and female
gametocytes pair up and release gametes (sexual
reproduction)
– Spore – gametes pair to form zygotes, and a protective
capsule is secreted

49.  Sporozoites
– Injected into blood by
mosquito
– Attack liver cells
 Merozoites
– Derived from sporozoites
– Reinfect liver cells or move to
red blood cells (RBCs)
– Reinfect RBCs, in pulses
 Cyclical merozoite release
correlates with cyclical
nature of malaria
symptoms
– Chills
– Fever
– Fatigue due to loss of
hemoglobin
– Serious damage due to the
blocking of capillaries by
infected (less pliable) RBCs

50.  Gametocytes
– Formed in RBCs, but do
not pair
– Release gametes in the
gut lumen of mosquito,
after being ingested
– Form zygotes which
penetrate gut wall and
encyst to form spore
– Sporozoites, produced in
spore, later migrate to
salivary glands
– Sporozoites released with
mosquito’s next blood
meal

51. Amoeboid Protozoa
 Posses pseudopodia for locomotion and prey capture
(heterotrophs)
 Have a complex cytoskeleton
 Marine, freshwater, and terrestrial species
 Same design found elsewhere in the animal kingdom
– Archeocytes of sponges
– Mammalian white blood cells (WBCs)
 Three main groups of amoeboid protozoans
– Amebas – 3 Phyla
– Phylum Foraminifera
– Phylum Actinopoda

52. Amebas
 Several important genera
that you will study in lab
– Amoeba
– Chaos
– Entamoeba
– Arcella
– Difflugia
 May or may not have a
test (lorica, theca)
 Arcella has dome shaped
test covering its top;
pseudopodia extend from
underneath
 Chaos can reach 5mm in
length

53.  Diversity of
pseudopodia
– Lobopodia – wide and
rounded
– Filopodia – slender and
may be branched
 Freshwater species
have one to several
contractile vacuoles
– No need in marine
species
 Some like Entomoeba
histolytica are
parasitic
– Causes dysentery

54. Phylum Foraminifera
 The forams
 Mostly marine
 Numerous
reticulopodia (special
filopodia) branch and
interconnect to form
reticulopodial network
 Vesicular traffic gives
reticulopods a
granular appearance

55.  Locomotion is
accomplished by
reticulopodial network
– Extends
– Anchors to substrate
– Retracts
 Forms a probing net that
is also used for finding
food
 Have a test, usually
composed of calcium
carbonate
 Most are
multichambered.
Usually start life
occupying one chamber,
but extend and secrete
new tests

56.  May be benthic or
planktonic, and there
are structural
differences between
the tests of the two
types
– Planktonic tests are
more fragile
– Also have spines to
increase surface area,
and thus buoyancy
 Foram tests create
natural wonders in the
form of chalk and
limestone
– Pink sands of Bermuda
– White Cliffs of Dover in
England
– Blocks of pyramids

57. Phylum Actinopoda
 Planktonic
 Spherical with a
perforated test
 Posses many axopodia
– Long, stiff, needle-like
pseudopodia
– Have microtubule support
rods
– Can attach and retract
– Used for flotation,
locomotion, and hunting

58.  Distinct cellular regions due to the
presence of a layer of pseudopodia
(not actinopods)
– Cortex – shroud of pseudopodia over the test.
Digests prey and transfers nutrients
– Medulla – inner portion of cell. Houses
nucleus, nutrients, or oil drops for buoyancy
 Divided into two classes
– Radiolaria
– Heliozoa

59. Class Radiolaria
 Marine
 Mostly planktonic
 Siliceous, spherical
test
 Large, up to 20cm
in some colonial
species

60. Class Heliozoa
 Sun animalcules
 Marine, freshwater, or
terrestrial (on
mosses)
 Contractile vacuoles in
freshwater species
 Similar to radiolarians