1. Chp 27
Bacteria & Archaea
Rob Swatski
Assistant Professor of Biology
HACC – York Campus
2. Overview: Masters of Adaptation
• Prokaryotes thrive almost everywhere, including
places too acidic, salty, cold, or hot for most other
organisms
• Most prokaryotes are microscopic, but what they lack
in size they make up for in numbersin size they make up for in numbers
• They have an astonishing genetic diversity
• There are more in a handful of fertile soil than the
number of people who have ever lived!!!
3. Structural & functional adaptations
contribute to prokaryotic success
• Prokaryotes are divided into two domains: Bacteria &
Archaea
• Most prokaryotes are unicellular, although some
species form coloniesspecies form colonies
• Most prokaryotic cells are 0.5–5 µm, much smaller than
the 10–100 µm of many eukaryotic cells
Bacteria on Cheek
Epithelial Cells - 5500X
4. • Prokaryotic cells have a variety of shapes
- the 3 most common shapes are spheres (cocci), rods
(bacilli), & spirals
6. Cell-Surface Structures
• An important feature of nearly all prokaryotic cells is their cell
wall
- maintains cell shape
- provides physical protection
- prevents the cell from bursting in a hypotonic environment
• Eukaryote cell walls are made of cellulose or chitin• Eukaryote cell walls are made of cellulose or chitin
• Bacterial cell walls contain peptidoglycan
- network of sugar polymers cross-linked by polypeptides
Peptidoglycan animation
7. • Archaea contain polysaccharides & proteins but lack
peptidoglycan
• Using the Gram stain, scientists classify many
bacterial species into Gram-positive & Gram-
negative groups based on cell wall composition
• Gram-negative bacteria:• Gram-negative bacteria:
- have less peptidoglycan
- outer membrane can be toxic
- more likely to be antibiotic resistant (many
antibiotics target peptidoglycan & damage cell
walls)
13. Some prokaryotes also have fimbriae (attachment pili)
- allows them to stick to substrates or to other individuals in colony
Sex pili are longer than fimbriae
- allow prokaryotes to exchange DNA
Fimbriae, UTI's, & Cranberry Juice
Fimbriae
14. Motility
• Most motile bacteria propel themselves by flagella -
structurally & functionally different from eukaryotic
flagella
• Many bacteria exhibit taxis, the ability to move toward
or away from certain stimulior away from certain stimuli
Chemotaxis!
16. Internal & Genomic Organization
Prokaryotic cells usually lack complex compartmentalization
But, some do have specialized membranes that perform
metabolic functions
18. • The prokaryotic genome has less DNA than the
eukaryotic genome
• Most of the genome consists of a circular chromosome
- the DNA is not surrounded by a membrane & is
located in a nucleoid region
• Some species of bacteria also have smaller rings of DNA
called plasmids
20. Reproduction & Adaptation
• Prokaryotes reproduce quickly by binary fission and can
divide every 1–3 hours
• Many form metabolically inactive endospores
- can remain viable in harsh conditions for centuries- can remain viable in harsh conditions for centuries
22. Prokaryotes can
evolve rapidly
because of their
short generation
times
EXPERIMENT
RESULTS
Daily serial transfer
0.1 mL
(population sample)
Old tube
(discarded
after
transfer)
New tube
(9.9 mL
growth
medium)
Fitnessrelative
toancestor
Generation
0 5,000 10,000 15,000 20,000
1.0
1.2
1.4
1.6
1.8
23. Prokaryotes have considerable genetic variation
3 factors contribute to this genetic diversity:
- Rapid reproduction
- Mutation
- Genetic recombination
24. Rapid Reproduction & Mutation
• Prokaryotes reproduce by binary fission
- offspring cells are generally identical
• Mutation rates during binary fission are low, but
because of rapid reproduction, mutations canbecause of rapid reproduction, mutations can
accumulate rapidly in a population
• High diversity from mutations allows for rapid
evolution
Binary Fission in Bacteria
25. Genetic Recombination
Prokaryotic DNA from different individuals can be brought
together by:
- transformation
- transduction
- conjugation- conjugation
26. Transformation: a cell takes up & incorporates foreign
DNA from the surrounding environment
Transformation in Bacteria
animation
Transduction: the movement of genes between bacteria
by bacteriophages (viruses that infect bacteria)
Bacteriophage animation
28. Conjugation:
- DNA is transferred between bacterial cells
- Sex pili allow cells to connect & pull together for DNA
transfer
• A piece of DNA called the “F” factor is required for the• A piece of DNA called the “F” factor is required for the
production of sex pili
- the F factor can exist as a separate plasmid or as DNA
within the bacterial chromosome
30. The “F” Factor as a Plasmid
“F” factor is transferable during conjugation as an F plasmid
• Cells with the F plasmid function as DNA donors during
conjugation
• Cells without the F plasmid function as DNA recipients• Cells without the F plasmid function as DNA recipients
during conjugation
31. F plasmid
F+ cell
Mating
bridge
Bacterial chromosome
F+ cell
Conjugation & recombination of an
F plasmid in E. coli
F– cell
bridge
Bacterial
chromosome F+ cell
The F- cell is the DNA recipient
32. The “F” Factor in the Chromosome
• A cell with the F factor built into its chromosomes
functions as a DNA donor during conjugation
• The recipient becomes a recombinant bacterium, with
DNA from 2 different cells
34. 4 Major Modes of Nutrition
• Photoautotrophy: obtain energy from light
• Chemoautotrophy: obtain energy from chemicals
• Photoheterotrophy: require CO2 as a carbon source• Photoheterotrophy: require CO2 as a carbon source
• Chemoheterotrophy: require an organic nutrient to
make organic compounds
35.
36. The Role of Oxygen in Metabolism
• Obligate aerobes: require O2 for cellular respiration
• Obligate anaerobes: are poisoned by O2 & use
fermentation or anaerobic respiration
• Facultative anaerobes: can survive with or without O2
37. Nitrogen Metabolism
• Prokaryotes can metabolize nitrogen in a variety of ways
• Nitrogen fixation: convert atmospheric nitrogen (N2) to
ammonia (NH3)
38. Metabolic Cooperation
• Metabolic cooperation: allows prokaryotes to use
environmental resources they could not use as individual
cells
• In the cyanobacterium Anabaena, photosynthetic cells &
heterocytes (nitrogen-fixing cells) exchange metabolicheterocytes (nitrogen-fixing cells) exchange metabolic
products
Cyanobacteria!
42. Molecular systematics is illuminating
prokaryotic phylogeny
Before the late 20th century, systematists based prokaryotic
taxonomy on phenotypic criteria
Applying molecular systematics to prokaryotic phylogeny
has produced dramatic resultshas produced dramatic results
- has led to a phylogenetic classification of prokaryotes
- major new clades have been identified
44. The use of polymerase chain reaction (PCR) has allowed
for more rapid sequencing of prokaryote genomes
- A handful of soil many contain 10,000 prokaryotic
species!!!
Horizontal gene transfer between prokaryotes obscures
the root of the tree of life
48. Extremophiles: live in harsh environments
• Extreme halophiles: live in very saline environments
• Extreme thermophiles: thrive in very hot environments
Extremophile Archaea
Acid-Loving Archaea
53. • Methanogens live in swamps & marshes
- produce methane as a waste product
- strict anaerobes & are poisoned by O2
In recent years, genetic prospecting has revealed many
new groups of Archaea
- some may offer clues to the early evolution of life
64. Chemical Cycling
Chemoheterotrophic prokaryotes: decomposers
- break down corpses, dead vegetation, & wastes
Nitrogen-fixing bacteria:Nitrogen-fixing bacteria:
- add usable N to the environment
69. Pathogenic prokaryotes typically cause disease by:
Exotoxins:
- cause disease even if the prokaryotes that produce
them are not present
Endotoxins:
- released only when bacteria die & cell walls break down
