Prokaryotes

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

8
(No Transcript)
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
• -Bergeys 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
• -Aids in attachment
• -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 -Release
d 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 O157H7 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 organisms 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