Bacteria and Archea : The Prokaryotes

1. Bacteria and Archea:The Prokaryotes

2. Archae & Bacteria There are almost everywhere !!! They are the most numerous organisms that can be found in all habitats

3. Prokaryotes • Appear approximately 3.5 BYA • Were the earliest living organisms • Have specialized into all habitats • Have all types of metabolism • Origin of aerobic and other types of respiration • Origin of several types of photosynthesis

4. Prokaryotes: Tremendous impact on the Earth • Very few cause diseases • As fixers and decomposers they are essential in geo-chemical cycles • Many form symbiotic relationships with other prokaryotes and eukaryotes • Mitochondria and chloroplasts may be descended from symbiotic bacteria

5. Prokaryotes as compared to eukaryotes: • Typically smaller in size • Lack membrane bound organelles • Most have cell walls – but different chemical composition • Have simpler genomes

6. Morphological Diversity of Prokaryotes • Cells have a diversity of shapes the most common being • spheres (cocci) • rods (bacilli) • helices (spirillaand spirochetes). • Prokaryotes are generally single-celled • some aggregate into two-celled to several celled groups • Some have specialized functions, heterocysts in Anabaena.

7. Fig 27.3

8. Domain Eukarya Eukaryotes Fig. 27-16 Korarcheotes Euryarchaeotes Domain Archaea Crenarchaeotes UNIVERSAL ANCESTOR Nanoarchaeotes Proteobacteria Chlamydias Spirochetes Domain Bacteria Cyanobacteria Gram-positive bacteria

9. Prokaryote Cell walls: • Cell walls: • Maintain the cell shape. • Protect the cell. • Prevent the cell from bursting in a hypotonic environment. • Eubacteria walls contain peptidoglycan • archae cell walls lack peptidoglycan • Peptidoglycan = Modified sugar polymers cross-linked by short polypeptides.

10. Gram Staining • Gram stain is used to distinguish two groups of eubacteria by structural differences in their cell walls. • Gram-positive eubacteria. • Cell walls with large amounts of peptidoglycan that react with Crystal Violet stain

12. Gram-negative eubacteria. • Have more complex cell walls with less peptidoglycan. • An outer lipopolysaccharide-containing membrane blocking the stain from the peptidoglycan. • Stain pink, with safranin • More likely to be disease causing

13. Fig 7.4 Prokaryote cell structure

14. Capsule= a gelatinous secretion which provides cells with additional protection • Pili = Surface appendages used for adherence to a host (in the case of a pathogen), or for transferring DNA in conjugate.

15. Fig 27.6 Pili

16. The Motility of Prokaryotes: three mechanisms : • Swimming with Flagella: differ from eukaryotic: • Solid protein • Rotate like an oar, rather than whip back and forth • The basal apparatus rotation is powered by the diffusion of protons into the cell.

17. Flagella

18. Fig 27.7

19. 2. Filaments • axial filaments are attached to basal motors at either end of the cell. • rotate the cell like a corkscrew. • more effective in viscous substrates than flagella. 3. Gliding • Some bacteria move by gliding through a layer of slimy chemicals secreted by the organism.

20. Taxis= Directed Movement towards or away from a stimulus. • light (phototaxis) • chemical (chemotaxis) • magnetic field (magnetotaxis) • Positive taxis movement toward a stimulus. • Movement away from a stimulus is a negative taxis

21. Non directional

22. Directional

23. Chemotaxis Test

24. Internal Membranous Organization • Some prokaryotes have specialized regions of internal membranes • formed by invaginations of the plasma membranes.

25. Fig 27.8 Specialized membranes

26. Prokaryotic Genomes • Genophore = usually one double-stranded, circular DNA molecule • attached to cell membrane.

27. Plasmid • Smaller independent rings of DNA • “extra genes” -antibiotic resistance or metabolism of unusual nutrients. • Replicate independently of the genophore. • Can be transferred between partners during conjugation • Also found in yeasts, (fungi - eukaryotes)

28. Amount of DNA

29. Genetic Recombination • Transformation = external DNA is incorporated by bacterial cells. • Conjugation = transfer of genes from one bacterium to another. • Transduction = transfer of genes between bacteria via viruses.

30. Conjugation

31. Fig. 27-13 F plasmid Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Recombinant F– bacterium A+ Hfr cell A+ A+ A+ F factor A– A+ A– A+ A– A– F– cell (b) Conjugation and transfer of part of an Hfr bacterial chromosome

32. Examples of Conjugation

33. Why is antibiotic resistance increasing ?

34. Gene Expression • Prokaryotic and eukaryotic DNA replication and translation are similar • Same genetic code • Bacterial ribosomes smaller and have different protein and RNA content

35. Cell Growth • They divide by Binary Fission. • Genophore attached to plasma membrane • Copies as membrane elongates • New wall forms in between • Mitochondria, chloroplasts divide by binary fission too • No Mitosis, nor Meiosis. • All haploid

36. Binary FissionFig. 12.10

37. Endospore = Resistant cells • Genophore surrounded by a thick wall.

38. Anthrax sp. endospore

39. Major Modes of Nutrition • Energy source (make ATP) • from light (phototrophs), • use chemicals in the environment (chemotrophs). • Carbon source • autotrophs utilize CO2 directly • heterotrophs require at least one organic nutrient as a carbon source.

40. Major Modes of Nutrition: • Photoautotrophs • Chemoautotrophs • Photoheterotrophs • Chemoheterotrophs

41. Table 27-1

42. Nutritional Diversity Among Chemoheterotrophs • Saprobes are decomposers that absorb nutrients from dead organic matter. • Parasites are cells that absorb nutrients from body fluids of living hosts • compounds that cannot be used as a carbon source by bacteria/fungi are termed non-biodegradable

43. Nitrogen Metabolism In amino acids, nucleotides • Nitrogen fixing bacteria (N2->NH3) • In soil, and some plant root nodules • Nitrifying bacteria convert NH3 -> NO2 • In soil, or biotower in treatment plant • Denitrifying bacteria N02 -(Nitrite) or N03 (Nitrate) to atmospheric N2 • In soil, counter-act fertilizers

44. The nitrogen fixing Cyanobacteria are very self-sufficient, they need only light energy, C02, N2, water and a few minerals to grow .

45. Oxygen metabolism • Obligate aerobes • Facultative anaerobes • Obligate anaerobes

46. Three Domains Fig 27.2

47. Domain Bacteria (Eubacteria) • a very diverse assemblage of organisms. • forms which exhibit every known mode of nutrition and energy metabolism.

48. Domain Archaea (Archaebacteria) • Cell walls lack peptidoglycan. • Plasma membranes have a unique lipid composition. • RNA polymerase and ribosomal protein are more like those of eukaryotes than of eubacteria • Common ancestor with Eukaryotes after split from Bacteria.

49. Domain Archaea (Archaebacteria) • Methanogens. • Use H2 to reduce C02 to CH4 and are strict anaerobes • In Digester at treatment plant • Extreme Halophiles • inhabit high salinity ( 15-20%) environments (e.g. Dead Sea). • Extreme Thermophiles • Live in habitats of 60 - 80C.

50. Hot springs Salt ponds