1. Chapter 27
Prokaryotes

2. Overview: They’re (Almost) Everywhere!
Most prokaryotes are microscopic
But what they lack in size they more than make up for in numbers
The number of prokaryotes in a single handful of fertile soil
Is greater than the number of people who have ever lived

3. Prokaryotes thrive almost everywhere
Including places too acidic, too salty, too cold, or too hot for most other organisms
Figure 27.1

4. Biologists are discovering
That these organisms have an astonishing genetic diversity

5. Most prokaryotes are unicellular
Concept 27.1: Structural, functional, and genetic adaptations contribute to prokaryotic success
Most prokaryotes are unicellular
Although some species form colonies

6. Prokaryotic cells have a variety of shapes
The three most common of which are spheres (cocci), rods (bacilli), and spirals
1 m
2 m
5 m
(a) Spherical (cocci)
(b) Rod-shaped (bacilli)
(c) Spiral
Figure 27.2a–c

7. Cell-Surface Structures
One of the most important features of nearly all prokaryotic cells
Is their cell wall, which maintains cell shape, provides physical protection, and prevents the cell from bursting in a hypotonic environment

8. Using a technique called the Gram stain
Scientists can classify many bacterial species into two groups based on cell wall composition, Gram-positive and Gram-negative
(a)
Gram-positive. Gram-positive bacteria have
a cell wall with a large amount of peptidoglycan
that traps the violet dye in the cytoplasm. The
alcohol rinse does not remove the violet dye,
which masks the added red dye.
(b)
Gram-negative. Gram-negative bacteria have less
peptidoglycan, and it is located in a layer between the
plasma membrane and an outer membrane. The
violet dye is easily rinsed from the cytoplasm, and the
cell appears pink or red after the red dye is added.
Figure 27.3a, b
Peptidoglycan
layer
Cell wall
Plasma membrane
Protein
Gram-
positive
bacteria
20 m
Outer
membrane
Lipopolysaccharide
negative

9. The cell wall of many prokaryotes
Is covered by a capsule, a sticky layer of polysaccharide or protein
200 nm
Capsule
Figure 27.4

10. Some prokaryotes have fimbriae and pili
Which allow them to stick to their substrate or other individuals in a colony
200 nm
Fimbriae
Figure 27.5

11. Motility Most motile bacteria propel themselves by flagella
Which are structurally and functionally different from eukaryotic flagella
Flagellum
Filament
Hook
Cell wall
Plasma
membrane
Basal apparatus
50 nm
Figure 27.6

12. In a heterogeneous environment, many bacteria exhibit taxis
The ability to move toward or away from certain stimuli

13. Internal and Genomic Organization
Prokaryotic cells
Usually lack complex compartmentalization

14. (a) Aerobic prokaryote (b) Photosynthetic prokaryote
Some prokaryotes
Do have specialized membranes that perform metabolic functions
(a) Aerobic prokaryote
(b) Photosynthetic prokaryote
0.2 m
1 m
Respiratory
membrane
Thylakoid
membranes
Figure 27.7a, b

15. The typical prokaryotic genome
Is a ring of DNA that is not surrounded by a membrane and that is located in a nucleoid region
Figure 27.8
1 m
Chromosome

16. Some species of bacteria
Also have smaller rings of DNA called plasmids

17. Reproduction and Adaptation
Prokaryotes reproduce quickly by binary fission
And can divide every 1–3 hours

18. Many prokaryotes form endospores
Which can remain viable in harsh conditions for centuries
Endospore
0.3 m
Figure 27.9

19. Rapid reproduction and horizontal gene transfer
Facilitate the evolution of prokaryotes to changing environments

20. Examples of all four models of nutrition are found among prokaryotes
Concept 27.2: A great diversity of nutritional and metabolic adaptations have evolved in prokaryotes
Examples of all four models of nutrition are found among prokaryotes
Photoautotrophy
Chemoautotrophy
Photoheterotrophy
Chemoheterotrophy

21. Major nutritional modes in prokaryotes
Table 27.1

22. Metabolic Relationships to Oxygen
Prokaryotic metabolism
Also varies with respect to oxygen

23. Facultative anaerobes
Obligate aerobes
Require oxygen
Facultative anaerobes
Can survive with or without oxygen
Obligate anaerobes
Are poisoned by oxygen

24. Prokaryotes can metabolize nitrogen
Nitrogen Metabolism
Prokaryotes can metabolize nitrogen
In a variety of ways
In a process called nitrogen fixation
Some prokaryotes convert atmospheric nitrogen to ammonia

25. Metabolic Cooperation
Cooperation between prokaryotes
Allows them to use environmental resources they could not use as individual cells

26. In the cyanobacterium Anabaena
Photosynthetic cells and nitrogen-fixing cells exchange metabolic products
Photosynthetic
cells
Heterocyst
20 m
Figure 27.10

27. In some prokaryotic species
Metabolic cooperation occurs in surface-coating colonies called biofilms
Figure 27.11
1 m

28. Until the late 20th century
Concept 27.3: Molecular systematics is illuminating prokaryotic phylogeny
Until the late 20th century
Systematists based prokaryotic taxonomy on phenotypic criteria
Applying molecular systematics to the investigation of prokaryotic phylogeny
Has produced dramatic results

29. Lessons from Molecular Systematics
Is leading to a phylogenetic classification of prokaryotes
Is allowing systematists to identify major new clades

30. A tentative phylogeny of some of the major taxa of prokaryotes based on molecular systematics
Domain Bacteria
Domain
Archaea
Eukarya
Alpha
Beta
Gamma
Epsilon
Delta
Proteobacteria
Chlamydias
Spirochetes
Cyanobacteria
Gram-positive
bacteria
Korarchaeotes
Euryarchaeotes
Crenarchaeotes
Nanoarchaeotes
Eukaryotes
Universal ancestor
Figure 27.12

31. Diverse nutritional types
Bacteria
Diverse nutritional types
Are scattered among the major groups of bacteria
The two largest groups are
The proteobacteria and the Gram-positive bacteria

32. Proteobacteria Figure 27.13 Rhizobium (arrows) inside a
root cell of a legume (TEM)
Nitrosomonas (colorized TEM)
Chromatium; the small
globules are sulfur wastes (LM)
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
Helicobacter pylori (colorized TEM).
2.5 m
1 m
0.5 m
Chromatium; the small
globules are sulfur wastes (LM)
10 m
5 m
Fruiting bodies of
Chondromyces crocatus,
a myxobacterium (SEM)
Bdellovibrio bacteriophorus
Attacking a larger bacterium
(colorized TEM)
2 m
Figure 27.13

33. Chlamydias, spirochetes, Gram-positive bacteria, and cyanobacteria
Chlamydia (arrows) inside an
animal cell (colorized TEM)
5 m
Leptospira, a spirochete
(colorized TEM)
5 m
1 m
Hundreds of mycoplasmas
covering a human fibroblast cell
(colorized SEM)
Streptomyces, the source of
many antibiotics (colorized SEM)
50 m
Figure 27.13
Two species of Oscillatoria,
filamentous cyanobacteria (LM)

34. Archaea share certaintraits with bacteria
And other traits with eukaryotes
Table 27.2

35. Some archaea Extreme thermophiles Live in extreme environments
Thrive in very hot environments

36. Extreme halophiles
Live in high saline environments
Figure 27.14

37. Methanogens Live in swamps and marshes
Produce methane as a waste product

38. Concept 27.4: Prokaryotes play crucial roles in the biosphere
Prokaryotes are so important to the biosphere that if they were to disappear
The prospects for any other life surviving would be dim

39. Prokaryotes play a major role
Chemical Recycling
Prokaryotes play a major role
In the continual recycling of chemical elements between the living and nonliving components of the environment in ecosystems

40. Chemoheterotrophic prokaryotes function as decomposers
Breaking down corpses, dead vegetation, and waste products
Nitrogen-fixing prokaryotes
Add usable nitrogen to the environment

41. Symbiotic Relationships
Many prokaryotes
Live with other organisms in symbiotic relationships such as mutualism and commensalism
Figure 27.15

42. Other types of prokaryotes
Live inside hosts as parasites

43. Some prokaryotes are human pathogens
Concept 27.5: Prokaryotes have both harmful and beneficial impacts on humans
Some prokaryotes are human pathogens
But many others have positive interactions with humans

44. Pathogenic Prokaryotes
Prokaryotes cause about half of all human diseases
Lyme disease is an example
5 µm
Figure 27.16

45. Pathogenic prokaryotes typically cause disease
By releasing exotoxins or endotoxins
Many pathogenic bacteria
Are potential weapons of bioterrorism

46. Prokaryotes in Research and Technology
Experiments using prokaryotes
Have led to important advances in DNA technology

47. Prokaryotes are the principal agents in bioremediation
The use of organisms to remove pollutants from the environment
Figure 27.17

48. Prokaryotes are also major tools in
Mining
The synthesis of vitamins
Production of antibiotics, hormones, and other products