This document provides information about the nutrition and feeding mechanisms of various parasites and protozoa. It discusses several different feeding methods including phagocytosis, pinocytosis, and absorption of dissolved nutrients. Specific examples are given for protozoan groups like rhizopods, kinetoplastids, apicomplexans, diplomonads, and ciliates. The feeding processes of individual parasites like Plasmodium and Giardia are also described.
6. HOW A PARASITE GETS NUTRIENT FROM
HOST?
2 system are employed by parasites:
a) Direct nutrients transfer through membranes
b) Through the involvement of various specialized
organs/ structures – permanent/temporary.
7. Based on the kinds of food/ nutrients taken in – 2 class of
protozoa
1) Phagothropic
– if protozoa takes in large particles of food
2 ) Saprozoic – Obtaining nourishment by absorption of
dissolved organic and inorganic materials
The manner of nutrition in Protozoa varies, depending on
species and where it lives.
8. PHAGOTHROPIC
Feeding by engulfing a food cell or particle and ingesting
it in a phagocytic vacuole
In Entamoebidae family, there is a structure called
pseudopodia (plural)/ pseudopodium (singular) involved
in feeding.
In ciliates there is a specialized groove or chamber in the
cell where phagocytosis takes place, called the cytostome
or mouth.
9. SPOROZOA
The Sporozoa are parasitic protozoans that lack
locomotor organs.
They have no cilia, no flagella, no pseudopods.
At some state in their life histories, they are usually
intracellular parasites.
The sporozoan can’t move or obtain food by itself and it
needs to depend on it’s host for transportation and to
obtain food.
Feeding on the cells and body fluids of a main organism
during their life cycle.
10. PART 1: PROTOZOA
Need to reiterate the following points:
- Protozoa consist of a single cell, although many species
contain more than one nucleus during all or portions of
their life cycles
- Cytoplasm contained with a membrane
- can be divided into ecto and endoplasm
- many organelles/ structures
- mitochondria, Golgi apparatus, lysosomes,
endoplasmic reticulum, ribosome, contractile
vacuoles, flagellum, cilium etc
11. a) Pentatrichomonas hominis, a
harmless commensal of the human
digestive tract.
b) A species of Trypanosoma, 15–30
μm, from the bloodstream of
vertebrates (both a and b have
undulating membranes).
c) Free-living Amoeba sp., 100–150 μm,
showing lobopodia.
d) Actinosphaerium sp., 200 μm (many
species are much smaller), with
actinopodia.
e) Arcella vulgaris, a freshwater shelled
ameba, about 100 μm with lobopodia.
f) Globigerina sp., a marine
foraminiferan up to 800 μm, with
filopodia.
g) Oocyst of Levineia canis, (35–42)
(27–33) μm, a coccidian parasite of
dogs.
h) Zoothamnium sp. colony, individuals
50–60 μm, colony up to 2 mm tall, an
obligate ectocommensal ciliate of
aquatic invertebrates.
i) Euplotes sp., 100–170 μm, a free-
living ciliate with ventral cirri and
prominent oral membranes.
j) Tetrahymena sp., ∼60 μm, a free-
living ciliate showing ciliary rows
(kineties)
12. ORGANELLES – WITH DIFFERENT FUNCTIONS
Mitochondria – respiration, exception – anaerobic
- Mitochondria, the organelles that bear enzymes of
oxidative phosphorylation and the tricarboxylic acid cycle,
often have tubular rather than lamellar cristae.
- In addition, some amebas have branched tubular
cristae, but in other protozoan groups the cristae may be
absent altogether.
- Mitochondria may be present as a single, large body, as
in some flagellates, or arranged as elongated, sausage-
shaped structures, as occur in pellicular ridges of some
ciliates.
Ribosomes, endoplasmic reticulum
– Secretory functions
13. Contractile vacuoles
– excretion of excess water
Flagellum and cilium
– locomotion and food gathering
Pseudopodia - are temporary extensions of the cell
membrane and
- are found in amebas as well as in a variety of cell
types in other organisms.
- Pseudopodia function in locomotion and feeding.
All this organelles directly involved with nutrition process
15. Take up dissolved organics directly across the cell
membranes,
The most common mechanisms of ingestion are pinocytosis
and phagocytosis.
The size of the food vacuoles varies greatly, depending on the
primarily on the size of the food materials ingested.
Ingestion can occur anywhere on the surface of the body,
there being no distinct cytostome.
Most rhizopodans are carnivores and frequently predaceous.
16. A food vacuole forms from invagination in the cell surface –
sometimes called a food cup – that pinches off and drops inward.
This process called endocytosis, occurs in response to stimulus at
the environment.
Vacuole formation in rhizopodans may be induced either mechanical
or chemical stimuli
Even nonfood items may be incorporated into food vacuoles, but they
are soon ingested.
Not only the size of food item, but also the amount of water taken in
during feeding determine the size of the food vacuole.
17. is the case when a molecule causes the cell membrane to bulge
inward, forming a vesicle
surrounding of food particles
- pushing of food particles into its cytoplasm
18. If live prey been ingested, they generally die within a few
minutes from the paralytic and proteolytic enzymes
present.
Undigested material that remains within the vacuole wall
reincorporated into cell membrane.
In most rhizopodans this process of cell defecation may
occur anywhere on the body, but in some active forms it
tend to take place at or near the trailing end of the moving
cell.
19. The streaming of protoplasm inside the
pseudopods moves the amoeba
forward.
Amoeba make contacts with a food
particle.
The pseudopods surround the particle.
After the food is corralled by the amoeba,
an opening in the membrane allows the
food particle to pass into the cell.
Inside the cell, the food is enclosed within
food vacuoles, digested by enzymes,
and assimilated by the amoeba.
The amoeba expels particles that are not
acceptable as food.
20. B) Uptake of dissolved
nutrients through a
pinocytotic channel in
Amoeba
C) Two ameba ingested
ciliates by phagocytosis.
22. All kinetoplastids are heterotropic.
Free-living bodonids capture particulate food, primarilly
bacteria, with the aid of anterior flagellum and ingest
through a permanent cytostome.
The cytostome leads to a cytopharynx which is supported
by microtubules
At the base of the cytopharynx, food is enclosed in food
vacuoles by endocytosis
24. Unfortunately, little is known about feeding mechanisms in
trypanosomes, all of which are parasitic.
Some trypanosomes have cytostome-cytopharyngeal complex
through which proteins are ingested.
The proteins are taken into food vacuoles by pinocyctosis at
the base of cytopharynx.
It has also reported that some trypanosomes can take in
proteins by pinocyctosis from the membrane lining the flagellar
pocket or by some sort of cell membrane mediated
mechanism.
25. PHYLUM APICOMPLEXA
An apicomplexan sporozoite or merozoite
illustrating the apical complex and other
structures typical of this life-cycle stage.
26. The alveoli are interrupted at both the anterior and posterior
ends, and at tiny invaginations of the cell membranes called
microspores, which have been implicated in feeding.
Nutrient ingestion is thought to occur primarily by pinocytosis
or phagocytosis at the microspores.
In the haemosporidians, ingestion of the host’s cytoplasm
through the microspores has been observed.
Absorption of the nutrients in some gregarines at the point
where the parasite attaches to the host’s cell.
27. B and C: The body of a
gregarine is commonly into
3 three recognizable
regions
28. PLASMODIUM
Malaria parasites transport carbohydrates, amino acids, purine
nucleosides, fatty acids, complex lipids, anions and cations
and the presence of the parasite confers upon the infected red
cell pathological alterations in nutrient transport that may
favour the development of the parasite.
The asexual stages of the parasite within the red cell lack
stored carbohydrate but require considerable quantities of
glucose to fuel their active metabolism and division.
Infected erythrocytes use between 10 and 50 times more
glucose than uninfected cells and the parasite appears to
induce permeability changes in the red cell membrane which
facilitate the passage of host glucose and amino acids into the
erythrocyte.
29. The nutritional source of amino acids for intracellular stages of
malaria is not fully understood; haemoglobin digestion
undoubtedly provides significant amounts, but the infected red
cell also shows increased transport of free amino acids in
culture.
In P. falciparum, these changes in amino acid transport rates
are first seen 15 hours after invasion and the infected
erythrocyte loses energy'coupled transport systems in favour
of diffusion; whether these amino acids enter the parasite itself
by carrier mediated transport or by diffusion remains to be
determined and awaits the development of methods permitting
culture of the asexual stages of the parasite outside the red
cell.
30. Malaria parasites transport exogenous purine nucleosides but
not pyrimidines.
This may be related to their inability to synthesize the purine
ring de novo.
Parasites liberated from red cells may accumulate certain
purines (e.g. adenosine, guanosine and hypoxanthine) and
can incorporate radioactivity from labelled adenosine, AMP
and ATP.
Several studies have demonstrated that lipids (i.e. free fatty
acids, cholesterol and phospholipid) are readily incorporated
into malaria parasites resident within the red cell but the
transport processes involved are unknown.
32. Most diplomonads are phagotrophic and feed on
bacteria.
These forms have a cytostome through which
endocytosis of the bacteria occur.
Other genera susch as Giardia lack of cytostomes and
are saprozoic, feeding by pinocytosis on mucous
secretions of the host’s intestinal tissue.
33. All parabasilids are heterotrophic and lack of cystome.
Fluid is taken up by pinocytosis in depression of cell surface.
Some take in by phagoctosis.
In heypermastigotes, pseudopodia formed in a sensitive region
at the posterior end of the cell engulf wood particles.
Trichomonads also form pseudopodia that engulf bacteria,
cellular debris and leukocytes
36. The ciliates include may different feeding types.
Some are filter feeders, other capture and ingest other
protista or small invertebrates, many eat algal filaments or
diatoms, some graze on attached bacteria, and a few are
saprophytic parasites.
In most ciliates, feeding is restricted to a specialized oral
area containing the cytostome or ‘the cell mouth’.
Food vacuoles are formed at the cytostome and then are
circulated through the cytoplasm a digestion occurs.
37. There are a variety of structures associated with, and
modifications of the cytostome.
Holozoic ciliates that ingest relatively large food items usually
possess a nonciliated tube – called the cytopharnx, which
extend from cytosome deep into the cytoplasm.
The wall of the cytopharynx often reinforced with rods of
microtubules (nematodesmata).
In Didinium, the cytopharynx is normally everted to form a
projection that sticks to prey and then inverts back into the cell,
thus pulling the prey into food vacuole.
38. In this way Didinium can engulf its relatively gigantic prey.
Other ciliates, such as hypostomes, have complex
nematodesmal baskets in which microtubules work
together to withdrawn filament of algae into cytostome,
reminiscent on the way sucks up a piece of spaghetti.
In most of these ciliates, the cilia around the mouth are
relatively simple
39. Other ciliates, including many of more familiar form (e.g
Stentor) are suspension feeders.
These often lack or have reduced cytopharynxes.
They have elaborate speciall oral cilia for creating water
currents, and filtering structures or scrapping devices.
Their cytostomes often sit in a depression on the cell
surface.
40. The size of food eaten by such ciliates depends on the nature
of feeding current and when present, the size of depression.
The oral ciliates often consists of compound ciliary organeles,
call the adoral zone of membranelles or simply the AZM, on the
other side of cytostome and a row of closely situated paired
cilia which is frequently called the paroral membrane on the
other side.
E.G Euplotes, Stentor, and Vorticella.
Many hypotrichs e.g Euplotes that move about the substratum
with their oral region oriented ventrally use their specialized
oral ciliature to swirl settle materials into suspension and then
into buccal cavity for ingestion.
42. Among the most specialized cialite feeding methods are
those use by suctorians, which lack cilia as adults and
instead have knobbed feeding tentacles.
A few suctorians, have two types of tentacles, one form
for food capture, and another one for digestion.
The swelling at the tips of the tentacles contains
extrusomes called haptocysts, which are discharged upon
contact with potential prey.
43. Portions of the haptocyst penetrate the victim and hold it
to the tentacle.
Sometime prey are actually paralysed after contact with
haptocycts, presumably by enzymes released during
discharge.
Following attachment to the prey, a temporary tube forms
within the tentacle and the contents of the prey are
sucked into tentacle and incorporated into food vacuoles
44. Phylum Ciliophora: Feeding in
suctorian ciliate Acinate.
A) Acinate has capitate feeding
tentacles; note the absence of
cilia
B) Contact with prey and firing of
haptocysts into prey
C) Shortening the tentacle and
formation of a temporary
feeding duct within the ring of
microtubules
D) Drawing of contents of prey into
duct and formation of food
vacuole
45. Several other types are extrusomes are present in the
ciliates.
Some predatory ciliates have tubular extrusomes, called
toxicysts, in the oral region of the cell.
During feeding, the toxicysts are extruded and release
their contents, which apparently include both paralytic and
digestive enzymes.
Active prey are first immobilised and then partially
digested food is later taken into food vacuoles.
46. Some ciliates have organelles called mucocysts located
on the beneath the pellicle.
Mucocysts discharge mucus onto the surface of the cell
as a protective coating; they may also play a role in cyst
formation.
Other have trichocysts, which contain nail-shaped
structures that can be discharged through the pellicle.
This structure serve a defensive function.
47. Extrusomes in ciliates:
A) Toxicysts
B) Mucocysts
C) The pellicle showing of mucocysts of (rised dots) just
below the surface
48. EXCRETION AND OSMOREGULATION
Most protozoa appear to be ammonotelic; that is, they
excrete most of their nitrogen as ammonia, most of which
readily diffuses directly through the cell membrane into
the surrounding medium.
Other sometimes unidentified waste products are also
produced, at least by intracellular parasites.
After these substances are secreted they are
accumulated within their host cell and, on the death of the
infected cell, have toxic effects on the host.
Carbon dioxide, lactate, pyruvate, and short-chain fatty
acids are also common waste products.
49. Contractile vacuoles are probably more involved with
osmoregulation than excretion.
Because free living, freshwater protozoa are hypertonic to
their environment, they imbibe water continuously by
osmosis.
Contractile vacuoles effectively pump out the water.
Marine species and most parasites do not form these
vacuoles, probably because they are more isotonic to
their environment.
However, Balantidium species have contractile vacuoles.
50. CONTRACTILE VACUOLE
Water is collected into the central ring of the vacuole and actively
transported from the cell