1. Prokaryotes
Chapter 28

2. The First Cells Microfossils are fossilized forms of microscopic life
-Oldest are 3.5 billion years old

3. The First Cells
Stromatolites are mats of cyanobacterial cells that trap mineral deposits
-Oldest are 2.7 billion years old

4. The First Cells
Isotopic analysis of carbon-12 in fossils suggests that carbon fixation was active as much as 3.8 BYA
Biomarkers are organic molecules of biological origin
-Lipids were found in ancient rocks
-This indicates that cyanobacteria are at least 2.7 billion years old

5. Prokaryotic Diversity
Prokaryotes are the oldest, and structurally simplest forms of life
Prokaryotes are ubiquitous
Less than 10% of species are known
Bacteria (also called eubacteria)
Archaea (formerly called archaebacteria)
-Many archaeans are extremophiles

6. Prokaryotic Features Unicellularity -Most are single-celled
-Some can form complex biofilms
Cell size
-Most are less than 1 mm in diameter
Chromosome
-Single circular double-stranded DNA
-Found in the nucleoid

7. Prokaryotic Features Internal compartmentalization
-No membrane-bounded organelles
Flagella
-Simple in structure; spin like propellers
Cell division
-Most divide by binary fission
Genetic recombination
-Occurs through horizontal gene transfer

9. Prokaryotic Features Metabolic diversity -Two types of photosynthesis
-Oxygenic = Produces oxygen
-Anoxygenic = Nonoxygen producing
- E.g: Sulfur and sulfate
-Chemolithotrophic prokaryotes derive energy from inorganic molecules

10. Bacteria vs. Archaea Plasma membrane -Bacterial lipids are unbranched
-Connected to glycerol by ester linkages
-Archaeal lipids are branched
-Connected to glycerol by ether linkages
-Tetraethers form a monolayer

11. Bacteria vs. Archaea

12. Bacteria vs. Archaea Cell wall -Bacteria have peptidoglycan
-Archaea lack peptidoglycan
DNA replication
-Archaeal DNA replication is more similar to that of eukaryotes
Gene Expression
-Archaeal transcription and translation are more similar to those of eukaryotes

13. Early Classification Characteristics
1. Photosynthetic or nonphotosynthetic
2. Motile or nonmotile
3. Unicellular or filamentous
4. Formation of spores or division by transverse binary fission
5. Importance as human pathogens or not

14. Molecular Classification
1. Amino acid sequences of key proteins
2. Percent guanine-cytosine content
3. Nucleic acid hybridization
4. Ribosomal RNA sequencing
5. Whole-genome sequencing

15. Molecular Classification
Based on these molecular data, several prokaryotic groupings have been proposed
-Bergey’s Manual of Systematic Bacteriology
-Contains about 7,000 bacterial and archaeal species
The three-domain (Woese) system of phylogeny is based on rRNA sequences

16. Molecular Classification

17. Prokaryotic Shapes Most prokaryotes have one of 3 basic shapes
-Bacillus = Rod-shaped
-Coccus = Spherical
-Spirillum = Helical-shaped

18. The Bacterial Cell Wall
Maintains shape and protects the cell from swelling and rupturing
Consists of peptidoglycan
-Polysaccharides cross-linked with peptides
Archaea do not possess peptidoglycan
-Some have pseudopeptidoglycan
Cell wall is the basis of the Gram stain

19. The Bacterial Cell Wall

20. The Bacterial Cell Wall
Two main types
-Gram-positive bacteria
-Thick peptidoglycan
-Teichoic and lipoteichoic acids
-Gram-negative bacteria
-Thin peptidoglycan
-Have an outer membrane
-Contains lipopolysaccharide

21. The Bacterial Cell Wall

22. External Layers S-layer
-A rigid paracrystalline layer found in some bacteria and archaea
-Aids in attachment
Capsule
-A gelatinous layer found in some bacteria
-Protects from the immune system

23. Bacterial Appendages Pili -Short, hairlike structures
-Found in Gram-negative bacteria
-Aid in attachment and conjugation
Flagella
-Long, helical structures
-Composed of the protein flagellin
-Involved in locomotion

24. Bacterial Appendages

25. Internal Structure Nucleoid region
-Contains the single, circular chromosome
-May also contain plasmids
Ribosomes
-Smaller than those of eukaryotes and differ in protein and RNA content
-Targeted by antibacterial antibiotics

26. Internal Structure Internal membranes -Invaginated cell membrane
-For respiration or photosynthesis
Endospores
-Highly-resistant structures
-Released upon cell lysis
-Can germinate back to normal cell

27. Prokaryotic Genetics Prokaryotes do not reproduce sexually
However, they undergo horizontal gene transfer, which is of three types
-Conjugation = Cell-to-cell contact
-Transduction = By bacteriophages
-Transformation = From the environment

28. Conjugation
In E. coli, conjugation is based on the presence of the F plasmid
F+ cells contain the plasmid
F- cells do not
The F+ cell produce an F pilus that connects it to an F- cell

29. Conjugation
Transfer of the F plasmid occurs through the conjugation bridge
The end result is two F+ cells

30. Conjugation The F plasmid can integrate into the bacterial chromosome
-Hfr cell (high frequency of recombination)
The F plasmid can also excise itself by reversing the integration process

31. Conjugation

32. Conjugation An inaccurate excision may occur -F’ cell
Conjugation can occur between an F’ and an F- cell
-The result is a partial diploid, or merodiploid

33. Transduction Generalized transduction
-Occurs via accidents in the lytic cycle
-Viruses package bacterial DNA and transfer it in a subsequent infection
-Virtually any gene can be transferred
Specialized transduction
-Occurs via accidents in the lysogenic cycle
-Imprecise excision of prophage DNA
-Only a few genes can be transferred

34. Transduction

35. Transformation Natural transformation
-Occurs in many bacterial species, including Streptococcus which was studied by Griffith
-DNA that is released from a dead cell is picked up by another live cell
Artificial transformation
-Accomplished in the lab
-Used to transform E. coli for molecular cloning

36. Transformation

37. Conjugative Plasmids Conjugative plasmids may pick up additional genes
-R (resistance) plasmids
-Encode antibiotic resistance genes
-Staphylococcus aureus
-Virulence plasmids
-Encode genes for pathogenic traits
-Enterobacteriaceae
-E. coli O157:H7 strain

38. Mutation Mutations can arise spontaneously in bacteria
-Also caused by radiation and chemicals
Mutations (and plasmids) can spread rapidly in a population
-Negative consequences for humans
-For example:
-Methicillin-resistance Staphylococcus aureus (MRSA)
-Vancomycin-resistant Staphylococcus aureus (VRSA)

39. Prokaryotic Metabolism
Acquisition of Carbon
-Autotrophs = From inorganic CO2
-Heterotrophs = From organic molecules
Acquisition of Energy
-Chemolithotrophs = From inorganic chemicals
-Phototrophs = From sunlight

40. Prokaryotic Metabolism
Photoautotrophs
-Cyanobacteria
Chemolithoautotrophs
-Nitrifiers
Photoheterotrophs
-Purple and green nonsulfur bacteria
Chemoheterotrophs
-Majority of prokaryotes
-Use organic molecules for C and energy

41. Prokaryotic Metabolism
Type III secretion system
-Found in many Gram-negative bacteria
-Used to transfer virulence proteins directly into host cells
-Yersinia pestis – Bubonic plague
-Pseudomonads – Plant pathogens
-Blights, soft rot, wilts

42. Human Bacterial Disease
In the early 20th century, infectious diseases killed 20% of children before the age of five
-Sanitation and antibiotics considerably improved the situation
In recent years, however, many bacterial diseases have appeared and reappeared

43. Human Bacterial Disease
Tuberculosis
-Mycobacterium tuberculosis
-A scourge for thousands of years
-Afflicts the respiratory system
-Mutidrug-resistant (MDR) strains are very alarming

44. Human Bacterial Disease
Dental caries (tooth decay)
-Plaque consists of bacterial biofilms
-Streptococcus ferments sugar to lactic acid
-Tooth enamel degenerates
Peptic ulcers
-Helicobacter pylori is the main cause
-Treated with antibiotics

45. Sexually transmitted diseases (STDs)
Gonorrhea
-Neisseria gonorrhoeae
-Can pass from mom to baby via birth canal
-Can cause pelvic inflammatory disease (PID)
Chlamydia
-Chlamydia trachomatis
-“Silent STD”
-Can cause PID and heart disease

46. Sexually transmitted diseases (STDs)
Syphilis
-Treponema pallidum
-Can pass from mom to baby via birth canal
-Four distinct stages
-Primary - Chancre
-Secondary - Rash
-Tertiary - Latency
-Quaternary - Heart and nerve damage

47. Sexually transmitted diseases (STDs)

48. Beneficial Prokaryotes
Prokaryotes are crucial to chemical cycles
-Decomposers release a dead organism’s atoms to the environment
-Photosynthesizers fix carbon into sugars
-Nitrogen fixers reduce N2 to NH3 (ammonia)

49. Beneficial Prokaryotes
Prokaryotes may live in symbiotic relationships with eukaryotes
-Mutualism = Both parties benefit
-Nitrogen-fixing bacteria on plant roots
-Cellulase-producing bacteria in animals
-Commensalism = One organism benefits and the other is unaffected
-Parasitism = One organism benefits and the other is harmed

50. Beneficial Prokaryotes
Bacteria are used in genetic engineering
- “Biofactories” that produce various chemicals, including insulin and antibiotics
Bacteria are used for bioremediation
-Remove pollutants from water, air and soil
-Exxon Valdez oil spill

51. Beneficial Prokaryotes