Lecture 5 Microbial eukaryotes: The diverse world of Protists Dr. Angelika Stollewerk

1. Chapter 27 Lecture 5Microbial eukaryotes: The diverse world of ProtistsDr. Angelika Stollewerk Leishmania major

2. Protists Aims: • To understand the diversity of protists • To appreciate the impact of protists on the world around them • To look closely at three examples in order to illustrate the basic biology of protists

3. Protists Aims: • To understand the diversity of protists • To appreciate the impact of protists on the world around them • To look closely at three examples in order to illustrate the basic biology of protists These lecture aims form part of the knowledge required for learning outcome 2: Describe basic organism structure and diversity (LOC2).

4. Protist Essential reading • pages 582-594 Recommended reading Pages 74-75: 4.3 What are the characteristics of eukaryotic cells (This will be covered in depth in SEF032 Molecules to Cells, but it is useful background here)

5. 27 The Origin and Diversification of the Eukaryotes • 27.1 How Do Microbial Eukaryotes Affect the World Around Them? • 27.2 How Did the Eukaryotic Cell Arise? • 27.3 How Did the Microbial Eukaryotes Diversify? • 27.4 How Do Microbial Eukaryotes Reproduce? (start of section)

6. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Eukaryotes that are neither plants, animals, or fungi are called protists, or microbial eukaryotes (though not all are microbial). They do not constitute a clade, they are paraphyletic. Their true phylogeny is the subject of research and debate.

7. Table 27.1 Major Eukaryote Clades (Part 1)

8. Table 27.1 Major Eukaryote Clades (Part 2)

9. Table 27.1 Major Eukaryote Clades (Part 3)

10. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? There is great diversity of microbial eukaryotes. Most are microscopic, but some are large (e.g., giant kelp). Many are constituents of plankton—free floating, microscopic, aquatic organisms. Plankton that are photosynthetic are called phytoplankton.

11. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? In marine food webs, phytoplankton are the primary producers. Diatoms (a clade) are dominant in the phytoplankton. They do one-fifth of the carbon fixation on Earth. The primary producers are consumed by heterotrophs.

12. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Endosymbiosis, in which one organism lives inside another, is common in microbial eukaryotes. Dinoflagellates are common endosymbionts in animals and other microbial eukaryotes; some are photosynthetic.

13. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Many radiolarians have photosynthetic endosymbionts. Often, both organisms benefit from the relationship. Some dinoflagellates live as endosymbionts in corals.

14. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Pathogens: Plasmodium—cause of malaria. Part of its life cycle is spent as a parasite in red blood cells. Female Anopheles mosquito is the vector; takes up Plasmodium gametes with the blood, zygotes form in mosquito gut. Plasmodium is passed to another human.

15. Figure 27.3 The Life Cycle of the Malarial Parasite

16. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Plasmodium’s complex life cycle makes it difficult to control. Best strategy—remove stagnant water where mosquitoes breed. Insecticides are also used. The genomes of Plasmodium falciparum, and Anopheles gambiae have been sequenced.

17. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Trypanosomes (kinetoplastids) are some of the most deadly organisms on Earth, causing sleeping sickness, leishmaniasis, and Chagas’ disease.

18. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Some chromalveolates, including diatoms, dinoflagellates, and haptophytes, can form “red tides.” Color is from pigments in dinoflagellates. Cell concentrations are extremely high. Some produce neurotoxins that kill fish. Gonyaulax produces a toxin that accumulates in shellfish.

19. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Coccolithophores (haptophytes) can also form immense blooms in the ocean. Blooms can reduce the amount of sunlight that penetrates deeper waters. Emiliania huxleyi—one of smallest unicellular eukaryotes. May contribute to global warming through its metabolism.

20. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Diatoms store oil as an energy reserve. Over millions of years, diatoms have died and sunk to the ocean floor, and through chemical and physical changes form petroleum and natural gas deposits.

21. 27.1 How Do Microbial Eukaryotes Affect the World Around Them? Foraminiferans secrete shells of calcium carbonate. Discarded shells make up extensive deposits of limestone. Some beach sands are made of fragments of foram shells. Foram shells are also used to date and characterize sedimentary rocks, and are used to infer temperatures from the past.

22. 27.2 How Did the Eukaryotic Cell Arise? Eukaryotic cells arose as the environment was changing dramatically—from anaerobic to aerobic. Major events that occurred in the evolution of eukaryote cells are still conjectural—a framework for thinking about this challenging problem.

23. 27.2 How Did the Eukaryotic Cell Arise? The main events: Origin of a flexible cell surface Origin of a cytoskeleton Origin of a nuclear envelope Appearance of digestive vesicles or vacuoles Endosymbiotic acquisition of some organelles

24. 27.2 How Did the Eukaryotic Cell Arise? Flexible cell surface: Prokaryotic cell wall was lost; cells can grow larger. As cell size increases, surface area-to-volume ratio decreases, but with a flexible surface, infolding can occur, creating more surface area. A flexible cell surface also allowed endocytosis to develop.

25. Figure 27.6 Membrane Infolding

26. 27.2 How Did the Eukaryotic Cell Arise? A cytoskeleton provided cell support, allowed cells to change shape, and move materials around the cell, including daughter chromosomes. In some cells microtubules gave rise to flagella. The nuclear envelope may have developed from the plasma membrane. The DNA of a prokaryote is attached to the plasma membrane; infolding of the membrane could have been the first step in development of the nucleus.

27. Figure 27.7 From Prokaryotic Cell to Eukaryotic Cell

28. 27.2 How Did the Eukaryotic Cell Arise? The next step was probably phagocytosis—the ability to engulf and digest other cells. The first true eukaryotes had a cytoskeleton and nuclear envelope; they probably had ER, Golgi apparatus, and perhaps flagella.

29. 27.2 How Did the Eukaryotic Cell Arise? Cyanobacteria were producing oxygen; at some point, some Eukarya incorporated proteobacteria that evolved into mitochondria—the endosymbiotic theory. The function of mitochondria initially might have been to detoxify O2 by reducing it to water. Later this became associated with ATP production.

30. 27.2 How Did the Eukaryotic Cell Arise? Some eukaryotes incorporated a prokaryote related to today’s cyanobacteria, which developed into chloroplasts. Evolution of chloroplasts probably occurred in a series of endosymbiotic events. Evidence comes from nucleic acid sequencing and electron microscopy.

31. 27.2 How Did the Eukaryotic Cell Arise? Primary endosymbiosis: All chloroplasts descended from a gram-negative cyanobacterium with an inner and outer membrane. A small amount of peptidoglycan from the bacterial cell wall is found today in the glaucophytes—the first group to branch off.

32. 27.2 How Did the Eukaryotic Cell Arise? Primary endosymbiosis gave rise to chloroplasts of green algae (chlorophytes and charophytes) and the red algae. Photosynthetic land plants arose from a green algal ancestor. Red algal chloroplasts retain some pigments that were present in the original cyanobacterium.

33. 27.2 How Did the Eukaryotic Cell Arise? Secondary and tertiary endosymbiosis gave rise to chloroplasts in the other microbial eukaryote groups. The euglenid ancestor engulfed a chlorophyte, retaining the chloroplasts. Euglenid chloroplasts have the same pigments as green algae and land plants, and has a third membrane.

34. Figure 27.8 Endosymbiotic Events in the Family Tree of Chloroplasts

35. 27.2 How Did the Eukaryotic Cell Arise? The cryptophytes (a clade of chromalveolates) engulfed a red algal cell that became the chloroplast. These chloroplasts contain reduced red algal nuclei, and appear to be a sister clade to all other chromalveolate chloroplasts.

36. 27.2 How Did the Eukaryotic Cell Arise? Dinoflagellates engaged in tertiary endosymbiosis: Karenia brevis lost its chloroplast and took up a haptophyte (a result of secondary endosymbiosis). One case of sequential secondary endosymbiosis—a dinoflagellate lost its red algal chloroplast and took up a chlorophyte.

37. 27.2 How Did the Eukaryotic Cell Arise? Uncertainties remain about the origins of eukaryotic cells. Lateral gene transfer complicates the study of relationships. Endosymbiosis does not account for all bacterial genes in eukaryotes. A recent suggestion is that Eukarya arose from the fusion of a gram-negative bacterium and an archaean.

38. 27.3 How Did the Microbial Eukaryotes Diversify? Microbial eukaryotes have evolved a diversity of lifestyles. Most are aquatic, marine and freshwater; but also damp soils and decaying organic matter. Some are photosynthetic, some are heterotrophs, some can switch between modes.

39. 27.3 How Did the Microbial Eukaryotes Diversify? Some used to be considered animals, and are called protozoans. But this term lumps phylogenetically unrelated groups. Most protozoans are ingestive heterotrophs. The term algae also lumps many groups of photosynthetic microbial eukaryotes and does not reflect phylogeny.

40. 27.3 How Did the Microbial Eukaryotes Diversify? Locomotion Amoeboid motion—cells form pseudopods that are extensions of the cell. A network of cytoskeletal microfilaments squeezes the cytoplasm forward.

41. 27.3 How Did the Microbial Eukaryotes Diversify? Cilia and flagella developed from microtubules. Cilia beat in a coordinated fashion; move cell forward or backward. Flagella have whip-like movement. Some pull, some push the cell forward. Flagella have a 9 + 2 arrangement of microtubules.

42. Figure 4.22 Sliding Microtubules Cause Cilia to Bend

43. Movement in the euglenid Eutreptia

44. 27.3 How Did the Microbial Eukaryotes Diversify? Vacuoles increase effective surface area in large cells. Contractile vacuoles in freshwater microbial eukaryotes such as Paramecium are used to excrete excess water.

45. Figure 27.10 Contractile Vacuoles Bail Out Excess Water

46. 27.3 How Did the Microbial Eukaryotes Diversify? Food vacuoles are formed by Paramecium and others when solid food particles are ingested by endocytosis. The food is digested in the vacuole. Smaller vesicles pinch off—increasing surface area for products of digestion to be absorbed by the rest of the cell. A Paramecium uses cilia for feeding

47. Figure 27.11 Food Vacuoles Handle Digestion and Excretion

48. 27.3 How Did the Microbial Eukaryotes Diversify? Cell surfaces Many microbial eukaryotes have diverse means of strengthening their surfaces. Paramecium has a covering of surface proteins called a pellicle, making it flexible but resilient. Other groups secrete a “shell,” such as foraminiferans.

49. 27.3 How Did the Microbial Eukaryotes Diversify? Some amoebas make a “shell” or test from bits of sand beneath the plasma membrane. Diatoms form glassy cell walls of silica. These walls are exceptionally strong, and perhaps enhanced defense against predators.

50. 27.4 How Do Microbial Eukaryotes Reproduce? Most microbial eukaryotes have both sexual and asexual reproduction. Asexual processes: Binary fission—equal splitting Multiple fission—splitting into more than two cells.