1. Prokaryotes (the fancy way to say Bacteria)
Chapter 27

2. Outline
Prevalence of Prokaryotes
Prokaryotic Diversity
Prokaryotic Complexity
Prokaryotic Variation
Prokaryotic Metabolism
Human Bacterial Diseases
Benefits of Prokaryotes

3. Prevalence of Prokaryotes
In almost every place or environment microbiologists (scientists who study small organisms) look, prokaryotes have been found.
Hot springs, hypersaline environments, highly toxic gaseous environment, within clean rooms of hospitals
In the 1980’s a new method of classification was used
Divided prokaryotes into 2 groups:
Archaebacteria (Archae) and bacteria

4. Prevalence of Prokaryotes
Prokaryotes are the oldest, structurally simplest, and most abundant forms of life on earth.
abundant for over 2 billion years before the appearance of eukaryotes
Prokaryotic synthesis (from cyanobacteria) is thought to have been the source for much of the earth’s oxygen in atmosphere
5,000 different kinds currently recognized

5. Structure of a Prokaryotic Cell

6. Structure of a Prokaryotic Cell
Most prokaryotic cells are small and lack interior organization.
The plasma membrane is enclosed within a rigid cell wall
DNA not contained within a membrane-bounded nucleus.
Prokaryotes exteriorly may have a flagellum and other outgrowths called pili.
Pili aid in attachment to other cells

7. Prevalence of Prokaryotes
Prokaryotic form
bacillus (bacilli) straight and rod-shaped
coccus (cocci) spherical shaped
spirillum (spirilla) long and helical shaped
Some bacillus and coccus bacteria form colonies
Spirilla generally do not form colonies and are often free swimming
Some bacterial colonies form spore producing structures.

8. Prevalence of Prokaryotes
Prokaryotic form
Coccus
Diplococcus
pairs
Streptococcus
chains
Tetrad
quads

9. Prevalence of Prokaryotes
Coccus
Sarcina
Staphalo

10. Prevalence of Prokaryotes
Bacillus
Single
Strepto
coccobacillus (no pics)

11. Prevalence of Prokaryotes
Spiral Types
Vibrio
Comma shaped
Sprillium
Thick rigid spiral
Spirochete
Thin flexible

12. Prevalence of Prokaryotes
Prokaryotes versus Eukaryotes
unicellularity
some may form filamentous matrices
cell size
1 μm or less in diameter
May vary by 5 orders of magnitude
chromosomes
“naked” (no protein) circular DNA located in nucleoid
cell division and recombination
binary fission (asexual)
internal compartmentalization
No internal compartments (mitochondria or chloroplasts)
only organelle is the ribosome
flagella
Single protein flagella of flagellin
Spin like propellers instead of whiplike
metabolic diversity
Several kinds of anaerobic and aerobic photosynthesis
Chemoautotrophs

13. Prokaryotic Diversity
Original key classification characteristics
photosynthetic or nonphotosynthetic
motile or nonmotile
unicellular or colony-forming or filamentous
spore formation by division or transverse binary fission

14. Prokaryotic Diversity
Now prokaryotic classification completed with genetic and molecular approaches
Analysis of amino acids sequence of key proteins
Nucleic acid analysis by establishing % guanine (G) and cytosine (C)
nucleic acid hybridization
ribosomal RNA sequencing
whole genome sequencing

15. Kinds of Prokaryotes
Very early, prokaryotes split into two lines
Archaea and bacteria are as different in structure and metabolism from each other as either is from eukarya.
Archae (archebacteria) not actually as old as Bacteria

16. Prokaryotic Diversity
Comparing archaebacteria and bacteria
plasma membranes
composed of different lipids
cell wall
archaebacteria lack peptidoglycan
gene translation machinery
Bacteria ribosomal proteins and RNA polymerases different from eukaryotes
archaebacteria similar to eukaryotes
gene architecture
bacteria genome not interrupted by introns
some archaebacteria posses introns

17. Prokaryotic Complexity
Prokaryotic cell surface – identifying features
cell wall maintains shape and protects the cell from swelling and rupturing
usually consist of peptidoglycan
Gram-positive - thicker peptidoglycan
(purple color after stain)
Gram-negative - thinner peptidoglycan
(red color after stain)
flagella – slender protein - locomotion
pili - hairlike structures – attachment (7.5 – 10 nm)
endospores - resistant to environment

18. Gram Stain

19. Flagellar Motor

20. The Cell Interior Internal membranes
invaginated plasma membrane for respiration and/or photosynthesis
Nucleoid region
lack nucleus - genes encoded with single double-stranded DNA
*Prokaryotes often posses plasmids: independently replicating circle of DNA that contain only a few genes (not usually essential for survival)
Ribosomes
Prokaryotic ribosomes are smaller than eukaryotic ribosomes, and differ in protein and RNA content.
Some antibiotics (tetracycline and chloramphenicol) bind to prokaryotic ribosomes to block protein synthesis

21. The Cell Interior Internal membranes
(a) aerobic bacterium exhibits extensive respiratory membranes within cytoplasm
(b) cyanobacterium has thylakoid-like membranes that provide sites for photosynthesis
Do you think that it is likely that photosynthetic and respiratory membranes evolved more than once?
How could your idea be tested experimentally?

22. Processes to Create Prokaryotic Variation
mutation
spontaneous errors in DNA replication
prokaryotic ability to mutate rapidly often has adverse effect on humans
Radiation, UV light, and various chemicals (mutagens) cause DNA replication errors
Normal mutation rate 1 per million bases
E. coli has 5000 genes
This means that 1 out of every 200 bacteria will have a mutation
1 spoonful of soil has 1 billion bacteria, so there should be 5 million mutant individuals per spoonful!

23. Processes to create Prokaryotic Variation
mutation
with sufficient nutrients, a typical bacterium population could double in 20 minutes.
this allows for mutations to spread rapidly
individual bacterium not killed by an antibiotic can then reproduce rapidly and after 30 generations (10 hours) there would be over 1 billion clones of this resistive bacteria
Some hospitals now have strains of Staphyloccus aureus that are penicillin resistant
Why then could antibiotic soaps be a problem?
Why should you take all 10 days of your medication?

24. Processes to create Prokaryotic Variation
mutation –figure 27.7

25. Processes to create Prokaryotic Variation
genetic recombination
occurs by gene transfer from one cell to another by viruses or conjugation
conjugation: temporary union of 2 unicellular organisms, during which genetic material is transferred from one cell to another.
this is another method that can lead to resistant bacteria

26. Prokaryotic Metabolism
Autotrophs
obtain carbon from inorganic CO2
photoautotrophs – use sunlight to build organic molecules from CO2
chlorophyll a as pigment and H20 as electron donor
bacteriochlorophyll as pigment and H2S as electron donor
chemoautotrophs - inorganic chemicals
obtain energy by oxidizing inorganic substances
Nitrifiers – oxidize ammonia or nitrite
On ocean floors H2S is oxidized as it escapes from thermal vents

27. Prokaryotic Metabolism
Heterotrophs
obtain carbon from organic molecules
photoheterotrophs – sunlight + organic C
purple non-sulfur bacteria
organic molecules such as carbohydrates or alcohols source for C
chemoheterotrophs (most prokaryotes)
carbon and energy from organic molecules
most decomposers and pathogens

28. Prokaryotic Metabolism
How heterotrophs infect host organisms
proteins secreted by type III system
may be used to transfer other virulence proteins into nearby eukaryotic cells

29. Human Bacterial Diseases
Tuberculosis
afflicts respiratory system and easily transmitted from person to person through the air
Dental caries
tooth decay caused by bacteria present in plaque
high sugar diets increase tooth decay
lactic acid bacteria ferment sugars and reduce pH, thus degenerating tooth enamel

30. Human Bacterial Diseases
Sexually transmitted diseases
Gonorrhea (Neisseria gonorrhoeae)
Syphilis (Treponema pallidum)
Chlamydia (Chlamydia trachomatis)

31. Benefits of Prokaryotes
Environment
chemical cycling
decomposition
nitrogen fixation
reduces N2 to NH3
Symbiotic properties
nitrogen-fixation
digestive tract of animals

32. Benefits of Prokaryotes
Genetic engineering
nonpolluting insect control
bioremediation
pollutant removal
biofactories
commercial production of antibiotics
Bioweapons
anthrax
smallpox

33. Bioremediation