Three Domains of Life

1. Three Domains of Life Protists

2. Three Domains of Life

3. Changes in Classification • The ‘old school’ method of classification included 5 Kingdoms (what I learned in school) • Monera • Protista • Fungi • Plantae • Animalia • Today, advances in molecular technology expanded our understanding (and interpretation) of systematics

4. Modern Systematics • Three Domain classification of life • Numerous, virtually countless Kingdoms • Bacteria and Archaea are now 2 distinct Domains (once included together in Kingdom Monera) • Protista, Fungi, Plantae, and Animalia remain classified as distinct Kingdoms, although classification of the kingdom Protista has been met with complications

5. Prokaryotes • Includes the kingdoms Archaea & Bacteria • Oldest, structurally-simplest, and most abundant forms of life • Photosynthesis  Bacterial and Eukaryotic Diversity • Important decomposers and symbionts

6. Prokaryotes • Unicellular • Typically 1μm or less (1000 μm = 1mm; 1000mm = 1 meter) • No membrane-bound nucleus; instead a single circular chromosome made of DNA • Asexual reproduction by binary fission • Photosynthetic bacteria utilize oxygen or chemical compounds, such as sulfur

7. Prokaryotic Cell Structure • Three basic forms: • Bacillus – rod-shaped • Coccus - sphercal or ovoid-shaped • Spirillum – spiral or helical

8. Prokaryotic Cell Structure • Prokaryotes have a tough cell wall and other external structures • Cell wall consists of peptidoglycan; a rigid network of polysaccharide strands cross-linked by peptide side chains; unique to Bacteria • Maintains the shape of the cell and protects it from swelling and rupturing

9. Prokaryotes can have 1 or more flagella (much less complex than in Eukaryotes) • Some Prokaryotes possess pilli, which helps fasten cell to host membrane

10. Domain Archaea • Once considered a subdivision of the Kingdom Monera, now its own domain • Like all prokaryotes, Archaea are single-celled microorganisms that lack a nucleus and membrane-bound organelles • Best known for the “extremophiles” – Archaea which thrive in extremely harsh environments

11. Archea - Extremophiles • Thermophiles – thrive at 60-80°C (>176°F!) • Acidophiles – thrive at pH at or below pH 3 • Xerophiles – grow in extremely dry conditions • Halophiles – require extremely high concentrations of salt http://www.dpchallenge.com/image.php?IMAGE_ID=448561

12. Archaea - Extremophiles • Evidence for evolution of life on Earth? • Many of the harsh conditions which extremophiles require to survive were characteristic of our early Earth • Likely that extremophiles evolved to dwell in such conditions billions of years ago and retained ability to survive today in specific environments

13. Archaea differ from Bacteria in numerous ways • Plasma membranes are made of different kinds of lipids • RNA and ribosomal proteins more like those of Eukaryotes • Mostly anaerobic Photosynthetic

14. Domain Bacteria • Two types: • Gram-positive • Gram negative • Refers to the Gram Stain (purple dye) • Gram-positive bacteria – possess a thicker peptidoglycan cell wall; retain stain • Gram-negative bacteria – contain less peptidoglycan; do not retain stain

15. Gram-positive and negative

16. Bacterial Conjugation • Transfer of genetic material • Horizontal gene transfer • NOT sexually (no gametes)

17. Eukaryotic origin • The nucleus and endoplasmic reticulum arose from infolding of the prokaryotic cell membrane

18. Eukaryotic origin • Eukaryotic organelles arose from a consortium of symbiotic prokaryotes • Mitochondria were aerobic heterotrophic prokaryotes • Chloroplasts (for photosynthesis) were photosynthetic prokaryotes

19. Endosymbiotic theory • Evidence? • Mitochondria have their own independent DNA, and a double membrane • Chloroplasts resemble cyanobacteria; also have their own independent DNA and a double membrane

21. Kingdom Protista (the trouble-maker) • Kingdom Protista is NOT monophyletic Paraphyletic – includes common ancestor but not all descendents

22. Kingdom Protista • Eukaryotic (must be! Domain Eukarya) • Largely unicellular withsome multi-cellular ‘exceptions’ (e.g., kelps, seaweed) • May be autotrophic or heterotrophic • Debate over classification – • Are some protists members of other kingdoms? • Would protists best be considered as several different kingdoms?

23. Kingdom Protista • Characterized by: • Mode of locomotion (e.g., flagella, cilia) • Mode of nutrition (e.g., autotrophic, heterotrophic) • Body form (unicellular, multicellular) • Pigmentation (e.g., Red, Green, Brown alga) • Reproduction (asexual, sexual) • Multicellular protists are distinguished from other Kingdoms by their lack of specialized tissues

24. Kingdom Protista

25. Kingdom Protista • Have you ever eaten a protist?, or should I ask, have you ever eaten seaweed??? • Just to complicate matters, green algae is categorized as a plant in Kingdom Plantae…

26. Green Plants evolved from Green Algae • We’ll come back to this…

27. Kingdom Fungi

28. Kingdom Fungi • Unicellular and multi-cellular • ~1.5 million species • Important decomposers • Includes many disease-causing organisms • Others are important symbionts and fermenting organisms

29. Kingdom Fungi • Mycology – the study of fungi • All fungi are heterotrophic • Obtain their food by secreting digestive enzymes and absorbing the nutrients released by the enzymes • Unicellular fungi may have flagella; multicellular fungi are primarily filamentous in form • Cell walls composed of chitin

30. Kingdom Fungi • Six phyla • Cytrids (flagellated), Zygomycetes (inc. bread molds), Glomeromycetes (mycorrhizae), Ascomycetes (inc. yeast), Bascidiomycetes (mushrooms), and Deuteromycetes (not pictured)

31. Kingdom Fungi • Phylogeny based on the 5 major Phyla (based on mode of sexual reproduction)

32. Kingdom Fungi • Multicellular fungi consist of long, slender filaments called hyphae • Some hyphae are continuous; others are divided by septa • Mycelium – a mass of connected hyphae

33. Kingdom Fungi • Mycelium grows through and digests its substrate • Fungi live in their food!

36. Kingdom Fungi • Hyphae (mycelium) form complex structures • A mushroom is a spore-bearing body of a fungus; composed of hyphae • A puffball is a spore-bearing body of certain species of fungi, including the deadly Death Cap mushroom; composed of hyphae

38. Kingdom Fungi • Fungi can also be monokaryotic or dikaryotic • Monokaryotic – one nucleus per cell • Dikaryotic – two nucleii per cell • Fungi reproduce sexually and asexually • During sexual reproduction in some fungi, 2 haploid nuclei fuse creating a dikaryotic (dikaryon) stage, which precedes the normal diploid nucleus

39. Kingdom Fungi • Some fungi produce specialized mycelial structures to house spores (e.g., mushroom, puffballs, ‘shelf’ mcycelium on dead trees) • Spores can form as a result of sexual or asexual reproduction • Spores can withstand degradation and survive for long periods of time; because of their size, they can travel long distances

41. Kingdom Fungi • Chestnut Blight – a fungal disease which has virtually eliminated the American chestnut • Accidentally introduced into the U.S. on imported lumber from Asia • The roots of the tree are fairly resistant to the fungus, but the tree succumbs once it grows enough shoots to reproduce • Unknown spreading agent (the spores are everywhere!)

42. Kingdom Fungi http://www.kychestnut.org/images/openGrownTree.jpg

43. …Jack Frost nippin’ at your nose… • The American chestnut once covered large tracts of forest in the U.S. • The chestnut was a very important source of food for wildlife (and the inspiration for at least 1 Christmas song…) • At the turn of the twentieth century, one quarter of all trees in the eastern United States were chestnut!

44. The Chestnut Blight • Only a few mature survivors remain of the American Chestnut, which once consisted of 4 billion trees (that’s over 99.99% gone) • If you have ever eaten a chestnut, you had a European import; only our grandparents may have ever tasted an American chestnut • The American Chestnut Foundation seeks to restore the great chestnut, but how?

45. The Chestnut Blight • Development of blight-resistant American chestnuts is accomplished through a process known as “backcross breeding” • Hybrids between American and Chinese chestnuts are repeatedly crossed back onto purely American specimens, yielding offspring which are blight- resistant • The resulting offspring are ~94% American (6% Chinese) and disease-resistant

46. Kingdom Fungi • Spores are frequently dispersed by wind, but may also be spread by insects and small animals • Chytrids are an ancestral group and retain flagella; have motile zoospores

47. Why did the mushroom go to the party? • Many fungi live underground, and can reach great sizes • One of the largest living organisms in the world is a fungus! • The largest known specimen covers more than 3.4 square miles and is thousands of years old • And some species of fungi are bioluminescent!

48. Armillaria fungus • Connected underground by hyphae!

49. Fungal Ecology • Fungi often have interactions or symbioses with other organisms • Obligate symbiosis – essential for survival; fungus cannot survive without symbiont • Facultative symbiosis – fungus can survive without symbiont • Mutualistic relationships – both partners benefit • Commensal relationships – one partner benefits, but the other is unaffected

50. Fungal Ecology • A lichen is a symbiotic association between a fungus and a photosynthetic partner (usually green algae or cyanobacteria)