1. Prokaryotes and the Origins of Metabolic Diversity
Chapter 27
Prokaryotes and the Origins of Metabolic Diversity

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. The Adaptive Ability of Prokaryotes
Prokaryotes thrive almost everywhere including places too acidic, too salty, too cold, or too hot for most other organisms
Figure 27.1

4. Bacteria and Archaea
Bacteria and Archaea are the two main branches of prokaryotic evolution.
Traditionally:
Prokaryotes were classified as Monera
New Scheme – 3 Domains:
Bacteria & Archaea
Archaea differ from bacteria structurally, biochemically, and physiologically.
Archaea tend to live in extreme environments.

5. The Three Domains of Life

6. Genetic Diversity of Prokaryotes
Biologists are discovering
That these organisms have an astonishing genetic diversity
Structural, functional, and genetic adaptations contribute to prokaryotic success
Most prokaryotes are unicellular
Although some species form colonies

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

8. 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
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

9. Gram Positive v/s Gram Negative Bacteria
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

10. Pathogenic Bacteria
Among pathogenic bacteria, gram-negative species are generally more threatening than gram-positive species.
They are commonly more resistant to antibiotics than gram positive species, and the lipopolysaccharides on their walls are often toxic.
Many antibiotics inhibit the synthesis of peptidoglycan in bacteria and thus prevent the formation of a functional cell wall – particularly in gram-positive species.

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

12. Attachment in Prokaryotes
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

13. 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

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

15. Internal and Genomic Organization
Prokaryotic cells usually lack complex compartmentalization although 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

16. The Prokaryotic Genome
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

17. Plasmids
Some species of bacteria also have smaller rings of DNA called plasmids
Plasmids are separate from the bacterial chromosome

18. Reproduction and Adaptation
Prokaryotes reproduce quickly by binary fission
And can divide every 1–3 hours
No mitosis or meiosis

19. Reproduction and Adaptation
Prokaryotes have three mechanisms that transfer genes between individuals:
Transformation
Transduction
Conjugation
Rapid reproduction and horizontal gene transfer
Facilitate the evolution of prokaryotes to changing environments

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

21. Major Nutritional Modes of Prokaryotes
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

22. Major Nutritional Modes of Prokaryotes
Chemoautotrophs are primary producers of deep sea communities associated with hot water vents.
Table 27.1

23. Nutritional Diversity Among Chemoheterotrophs
The majority of known prokaryotes are chemoheterotrophs:
Saprobes (decomposers that absorb their nutrients from dead organic matter)
Parasites (absorb nutrients from the body fluids of living hosts)

24. Metabolic Relationships to Oxygen
Prokaryotic metabolism also varies with respect to oxygen
Obligate aerobes
Require oxygen
Facultative anaerobes
Can survive with or without oxygen
Obligate anaerobes
Are poisoned by oxygen

25. Prokaryotes can metabolize nitrogen in a variety of ways
Nitrogen Metabolism
Prokaryotes can metabolize nitrogen in a variety of ways
In a process called nitrogen fixation some prokaryotes convert atmospheric nitrogen (N2) to ammonia (NH4)
Nitrogen fixation is the only biological mechanism that makes atmospheric nitrogen available to organisms for incorporation into organic compounds.

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

27. Halophiles Extreme halophiles Live in high saline environments
Figure 27.14

28. Mehtanogens Methanogens Live in swamps and marshes
Produce methane as a waste product
Important decomposers in sewage treatment
Can convert garbage and dung to methane

29. Prokaryotes and the Biosphere
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

30. 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
Chemoheterotrophic prokaryotes function as decomposers
Breaking down corpses, dead vegetation, and waste products
Nitrogen-fixing prokaryotes**
Add usable nitrogen to the environment

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

32. Prokaryotic Interactions
Other types of prokaryotes
Live inside hosts as parasites
Prokaryotes have both harmful and beneficial impacts on humans
Some prokaryotes are human pathogens
But many others have positive interactions with humans

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

34. Pathogenenic Prokarytoes
Pathogenic prokaryotes typically cause disease by releasing exotoxins or endotoxins
Exotoxins are proteins secreted by prokaryotes that can produce disease symptoms even in the absence of the bacterium:
Botulism
Cholera
Endotoxins are components of the outer membranes of gram-negative bacteria
Salmonella
Many pathogenic bacteria
Are potential weapons of bioterrorism

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

36. Prokaryotes are the principal agents in bioremediation
The use of organisms to remove pollutants from the environment
Sewage treatment, oil spill clean ups, commercial products
Figure 27.17

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