Chapter 2 Introduction to Protozoa

1. Chapter 2 Introduction to Protozoa

2. 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

3. 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

4. Protozoan Diversity

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

6. 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

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

8. 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)

9. 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

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

11. 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

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

13. 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

14. 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

15. 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

17. The consequences of being an osmoconformer

18. 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)

19. 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

20. 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

21. 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

22. 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

23. Chapter 3 - Protozoa

24. 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

25. 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

26. 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

27. Phylum Euglenozoa • Two main classes • Euglenoidea • Kinetoplastida • Both are flagellates • Both reproduce asexually • Both are solitary

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

29. 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

30. 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

31. 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

32. 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

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

34. 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

35. 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

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

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

38. 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

39. Phylum RetortamonadaorMetamonada • 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.”(Giardiasis)

40. 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

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

42. Alveolata The most notable shared characteristic is the presence of cortical alveoli, flattened vesicles packed into a continuous layer supporting the membrane, typically forming a flexible pellicle. In dinoflagellates they often form armor plates.

43. 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

44. 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

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

46. 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

47. 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

48. 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

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

50. Ciliates have two types of nuclei • Macronucleus – genes are actively transcribed • Micronucleus – master copy of genome; inactive except during cell division. Theyarediploidwithlittle RNA • Shapes and numbers (1 to 20) of these nuclei varies across genera • Bean shaped in Paramecium • String of beads in Stentor