1. Chapter 27
Bacteria and Archaea

2. Overview: Masters of Adaptation
Prokaryotes:
Thrive almost everywhere
In too acidic, salty, cold, or hot for most other organisms
Most are microscopic
Lack in size but make up for it in numbers
Have an astonishing genetic diversity
Divided into two domains:
Bacteria
Archaea

3. Fig. 27-1
Figure 27.1 Why is this lakebed red?

4. Most prokaryotes are unicellular Some form colonies
Concept 27.1: Structural and functional adaptations contribute to prokaryotic success
Most prokaryotes are unicellular
Some form colonies
Cells are much smaller (0.5–5 µm) than eukaryotic cells (10–100 µm)
The cell wall is a key feature in nearly all of them
Cells have a variety of shapes
The three most common cell shapes are:
Spheres (cocci)
Rods (bacilli)
Spirals

5. (a) Spherical (cocci) (b) Rod-shaped (bacilli) (c) Spiral 1 µm 2 µm
Fig. 27-2
Figure 27.2 The most common shapes of prokaryotes
1 µm
2 µm
5 µm
(a) Spherical
(cocci)
(b) Rod-shaped
(bacilli)
(c) Spiral

6. Cell-Surface Structures
The importance of prokaryotic cell wall:
Maintains cell shape
Provides physical protection
Protect the cell from bursting in a hypotonic environment
Bacterial cell walls:
Contain peptidoglycan (a network of sugar polymers cross-linked by polypeptides)

7. Gram-negative bacteria:
Archaea:
Contain polysaccharides and proteins
But lack peptidoglycan
Using Gram stain, & based on cell wall composition, many bacteria are classified into:
Gram-positive
Gram-negative
Gram-negative bacteria:
Have less peptidoglycan
Have an outer membrane that can be toxic
More likely to be antibiotic resistant

8. Many antibiotics work by:
Targeting peptidoglycan & damage the bacterial cell walls
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Peptidoglycan
layer
Cell
wall
Cell
wall
Peptidoglycan
layer
Plasma membrane
Plasma membrane
Protein
Protein
Gram-
positive
bacteria
Gram-
negative
bacteria
Figure 27.3 Gram staining
20 µm
(a) Gram-positive: peptidoglycan traps
crystal violet.
(b) Gram-negative: crystal violet is easily rinsed away,
revealing red dye.
Fig. 27-3

9. (a) Gram-positive: peptidoglycan traps crystal violet.
Fig. 27-3a
Peptidoglycan
layer
Cell
wall
Plasma membrane
Protein
Figure 27.3 Gram staining
(a) Gram-positive: peptidoglycan traps
crystal violet.

10. of lipopolysaccharide
Fig. 27-3b
Carbohydrate portion
of lipopolysaccharide
Outer
membrane
Cell
wall
Peptidoglycan
layer
Plasma membrane
Protein
Figure 27.3 Gram staining
(b) Gram-negative: crystal violet is easily rinsed
away, revealing red dye.

11. Gram- Gram- positive negative bacteria bacteria 20 µm Fig. 27-3c
Figure 27.3 Gram staining
Gram-
positive
bacteria
Gram-
negative
bacteria
20 µm

12. Capsule: A polysaccharide or protein layer covers many prokaryotes
200 nm
Capsule

13. Fimbriae (attachment pili):
Found in some prokaryotes
Allow prokaryotes to stick to their substrate or other individuals in a colony
Sex pili:
Are longer than fimbriae, and
Allow prokaryotes to exchange DNA

14. Fig. 27-5
Figure 27.5 Fimbriae
Fimbriae
200 nm

15. Video: Prokaryotic Flagella (Salmonella typhimurium)
Motility
Most motile bacteria propel themselves by flagella
Prokaryotic flagella are structurally and functionally different from eukaryotic flagella
In a heterogeneous environment, many bacteria exhibit a phenomenon called taxis
Taxis:
is the ability to move toward or away from certain stimuli
Video: Prokaryotic Flagella (Salmonella typhimurium)

16. Flagellum Filament Cell wall Hook Basal apparatus Plasma membrane
Fig. 27-6
Flagellum
Filament
50 nm
Cell wall
Hook
Basal apparatus
Figure 27.6 Prokaryotic flagellum
Plasma
membrane

17. Filament Cell wall Hook Basal apparatus Plasma membrane Fig. 27-6a
Figure 27.6 Prokaryotic flagellum
Plasma
membrane

18. Prokaryotic flagellum (TEM)
Fig. 27-6b
50 nm
Figure 27.6 Prokaryotic flagellum
Prokaryotic flagellum (TEM)

19. Internal and Genomic Organization
Prokaryotic cells:
Usually lack complex compartmentalization
Some do have specialized membranes that perform metabolic functions

20. (a) Aerobic prokaryote (b) Photosynthetic prokaryote
Fig. 27-7
0.2 µm
1 µm
Respiratory
membrane
Figure 27.7 Specialized membranes of prokaryotes
Thylakoid
membranes
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote

21. Some species of bacteria also have:
Prokaryotic genome:
Has less DNA than the eukaryotic genome
Mostly consists of a circular chromosome
Some species of bacteria also have:
Smaller rings of DNA called plasmids

22. Chromosome Plasmids 1 µm Fig. 27-8
Figure 27.8 A prokaryotic chromosome and plasmids
1 µm

23. The typical prokaryotic genome is:
A ring of DNA
The DNA is:
Not surrounded by a membrane
Located in a nucleoid region

24. Reproduction and Adaptation
Prokaryotes reproduce quickly by:
Binary fission & divide every 1–3 hours
Some every 20 min
Many form metabolically inactive endospores
Endospores can be viable in harsh conditions for centuries
Prokaryotes can evolve rapidly because of their short generation times

25. Fig. 27-9
Endospore
Figure 27.9 An endospore
0.3 µm

26. 0.1 mL (population sample) Fitness relative to ancestor
Fig
EXPERIMENT
Daily serial transfer
0.1 mL
(population sample)
Old tube
(discarded
after
transfer)
New tube
(9.9 mL
growth
medium)
RESULTS
1.8
1.6
Figure Can prokaryotes evolve rapidly in response to environmental change?
Fitness relative
to ancestor
1.4
1.2
1.0
5,000
10,000
15,000
20,000
Generation

27. Promotion of genetic diversity in prokaryotes
Prokaryotes have considerable genetic variation
Three factors contribute to this genetic diversity:
Rapid reproduction
Mutation
Genetic recombination

28. Rapid Reproduction and Mutation
Prokaryotes reproduce by binary fission
Offspring cells are generally identical
Mutation rates during binary fission are low
But mutations can accumulate rapidly in a population, due to rapid reproduction
High diversity from mutations allows for rapid evolution

29. Genetic Recombination
Additional diversity arises from genetic recomb-ination
Prokaryotic DNA from different individuals can be brought together by:
Transformation:
Incorporation of foreign DNA from the environment
Transduction:
Movement of genes between bacteria by bacteriophages (bacterial viruses)
Conjugation:
Transfer of genetic material between bacterial cells

30. Fig
Phage DNA A+ B+
What type of proccess? A+ B+
Donor
cell A+
Recombination
Figure Transduction A+ A– B–
Recipient
cell A+ B–
Recombinant cell

31. Conjugation and Plasmids
In conjugation:
Sex pili allow cells to connect & pull together for DNA transfer
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

32. Fig
Figure Bacterial conjugation
1 µm
Sex pilus

33. The F Factor as a Plasmid
Cells containing the F plasmid function as DNA donors during conjugation
Cells without the F factor function as DNA recipients during conjugation
The F factor is transferable during conjugation

34. Fig
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
Hfr cell A+ A+ A+
F factor
Figure Conjugation and recombination in E. coli A+ A– A+ A– A– A+ A–
F– cell
(b) Conjugation and transfer of part of an Hfr bacterial chromosome

35. The F Factor in the Chromosome
The donor cell (during conjugation):
The cell with the F factor built into its chromosomes
The recipient bacterium: :
The recombinant bacterium with DNA from two different cells
It is assumed that horizontal gene transfer is also important in archaea

36. R Plasmids and Antibiotic Resistance
R plasmids carry genes for antibiotic resistance
Antibiotics select for bacteria with genes that are resistant to the antibiotics
Antibiotic resistant strains of bacteria are becoming more common

37. Phototrophs obtain energy from light
Evolvement of diverse nutritional & metabolic adaptations in prokaryotes
Phototrophs obtain energy from light
Chemotrophs obtain energy from chemicals
Autotrophs require CO2 as a carbon source
Heterotrophs require an organic nutrient to make organic compounds
Accordingly, the four major modes of nutrition:
Photoautotrophy
Chemoautotrophy
Photoheterotrophy
Chemoheterotrophy

38. Table 27-1
Table 27-1

39. The Role of Oxygen in Metabolism
Prokaryotic metabolism varies with respect to O2:
Obligate aerobes require O2 for cellular respiration
Obligate anaerobes are poisoned by O2 and use fermentation or anaerobic respiration
Facultative anaerobes can survive with or without O2

40. Prokaryotes can metabolize nitrogen in a variety of ways:
Nitrogen Metabolism
Prokaryotes can metabolize nitrogen in a variety of ways:
Nitrogen fixation:
Some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH3)
Cooperatve use of environmental resources that can’t be used by individual cells;
Example: photosynthetic cells & nitrogen-fixing cells called heterocytes (in cyanobacterium Anabaena) exchange metabolic products

41. Photosynthetic cells Heterocyte 20 µm Fig. 27-14
Figure Metabolic cooperation in a colonial prokaryote
20 µm

42. Concept 27.4: Molecular systematics is illuminating prokaryotic phylogeny
Until the late 20th century prokaryotic taxonomy was based on phenotypic criteria
Later use of molecular systematics has produced dramatic results
Polymerase chain reaction (PCR) allowed for more rapid sequencing of prokaryote genomes

43. Archaea
Archaea share certain traits with bacteria and other traits with eukaryotes
Eukarya
Archaea
Bacteria

44. Table 27-2
Table 27.2

45. Extremophiles: Archaea that live in extreme environments:
Extreme halophiles:
Those live in highly saline environments
Extreme thermophiles:
Those thrive in very hot environments

46. Fig
Figure Extreme thermophiles

47. Methanogens: Live in swamps and marshes
Produce methane as a waste product
Strict anaerobes and are poisoned by O2

48. Bacteria Bacteria: Include the vast majority of prokaryotes
Diverse nutritional types are scattered among the major groups of bacteria

49. Gram-negative bacteria Include:
Proteobacteria
Gram-negative bacteria
Include:
Photoautotrophs
Chemoautotrophs
Heterotrophs
Some are anaerobic, others aerobic