1. Lecture 86 – Lecture 87 – Lecture 88 – Lecture 89 Bacteria Ozgur Unal
NIS - BIOLOGY
Lecture 86 – Lecture 87 – Lecture 88 – Lecture 89
Bacteria
Ozgur Unal

2. Bacteria
What do cheese, wine and strep throat
have in common?

3. Diversity of Prokaryotes
Remember prokaryotic cells?
What does prokaryote mean?
Bacteria are microscopic organisms that are prokaryotes.
Prokaryotes are very important for human body, food production, industry and environment.
Prokaryotes are:
First organisms on Earth
Most numerous organisms on Earth
All prokaryotes (eubacteria and archaea) were previously classified into the Kingdom Monera.
Today, the prokaryotes are divided into two domains:
Domain Bacteria  Eubacteria
Domain Archaea  Archaebacteria

4. Diversity of Prokaryotes
Eubacteria:
When most people read about or hear the word bacteria, they think of eubacteria.
Eubacteria are the most studied organisms and found almost everywhere except in the extreme environments where mostly archaebacteria are found.
Eubacteria have very strong cell walls
that contain peptidoglycan.
Some eubacteria are
photosynthetic  Example: Cyanobacteria

5. Diversity of Prokaryotes
Archaebacteria:
In extreme environments that are hostile to most other forms of life, archaebacteria predominate.
Example: Thermoacidophiles live in hot, acidic environments (pH 1-2 and temperatures above 80 oC).
Halophiles live in salty environments  Salt concentration around 15 %
Halophiles are usually aerobic.
Some of them perform a unique form of
photosynthesis using a protein instead of
the pigment chlorophyll.

6. Diversity of Prokaryotes
Archaebacteria:
Methanogens are the third group of archaebacteria.
These organisms are obligate anaerobes  cannot live in the presence of oxygen.
They use carbon dioxide during respiration and give off methane as a waste product.
They are found in sewage treatment plants, swamps, bogs and near volcanic vents AND even in your body!
What are the differences between
eubacteria and archaebacteria?

7. Prokaryote Structure
Prokaryotes are microscopic, unicellular organisms without a nucleus and membrane-bound organelles.
The genes of a prokaryote are found on a large, circular chromosome in an area of the cell called nucleoid.
Many prokaryotes also have at least one
smaller piece of DNA, called a plasmid.
Some prokaryotes secrete a layer of
polysaccharides around the cell wall,
forming a capsule.
The capsule:
prevents the cell from drying out
helps the cell attach to surfaces in its environment
protects the cell against white blood cell

8. Prokaryote Structure
Structure called pili are found on the outer surface of some bacteria.
Pili are submicroscopic hairlike structures that are made of protein.
It helps bacterial cells attach to
surfaces.
Serves as bridge between cells..
Prokaryotes are smaller than
eukaryotes.
They are typically only 1 to 10 µm
long and 0.7 to 1.5 µm wide.
Check out Figure 18.4!!

9. Identifying Prokaryotes
Today, prokaryotes can be identified using molecular techniques  DNA comparison  Evolutionary relationships
Historically, scientists identified bacteria using criteria such as shape, cell wall and movement.
Shape:
There are three general shapes of
prokaryotes: cocci, bacilli and spirochetes.

10. Identifying Prokaryotes
Cell walls:
Composition of cell wall is used to
classify eubacteria.
A method, called Gram stain is used to
distinguish two types of bacteria.
Gram-positive  large amount of peptidoglycan (dark purple)
Gram-negative  less peptidoglycan (light pink)
Movement:
Some prokaryotes are stationary, but
some use flagella for movement.
Flagella help prokaryotes move toward light, higher oxygen concentration or chemicals such as sugar or amino acids.

11. Reproduction of Prokaryotes
Most prokaryotes reproduce by an asexual
process called binary fission.
Binary fission is the division of a cell into two genetically identical cells.
Under ideal environmental conditions, binary
fission can occur as often as every 20 minutes.
How many bacteria can be produced from
one bacterium in 10 hours?
Some prokaryotes can exchange genetic
information  conjugation
In conjugation, two prokaryotes attach to each other and exchange their DNA with the help of their pili  Figure 18.6!!

12. Metabolism of Prokaryotes
Eubacteria and archaebacteria can be grouped based on how they obtain energy for cellular respiration.
Check out Figure 18.7!!
Photoautotrophs:
Some bacteria are photosynthetic autotrophs  they carry out photosynthesis in a similar manner as plants
What kind of environments do they live in?
These type of bacteria are also called cyanobacteria.
Cyanobacteria are thought to have been the
first group of organisms to release oxygen into
Earth’s early atmosphere.

13. Metabolism of Prokaryotes
Chemoautotrophs:
These organisms break down and release inorganic compounds that contain nitrogen or sulfur, such as ammonia and hydrogen sulfide, in a process called chemosynthesis  no need for O2
Chemoautotrophs are important for cycling of certain organic chemicals in nature.
Aerobes and Anaerobes:
Bacteria also vary in whether or not they can grow in the presence of oxygen.
Obligate aerobes  require oxygen
Obligate anaerobes  do not use oxygen (fermentation)
Facultative anaerobes  grow either in the presence of oxygen or anaerobically by using fermentation

14. Survival of Bacteria
How can bacteria can survive if their environment becomes unfavorable? Lack of water, extreme temperature changes etc..
Endospores:
When environmental conditions are harsh, some types of bacteria produce a structure called an endospore.
Example: Bacteria that cause anthrax, botulism and tetanus are endospore producers.
An endospore can be thought of as a dormant cell.
They are resistant to harsh environments and might be able to survive:
extreme heat
Extreme cold
dehydration
large amounts of UV radiation

15. Survival of Bacteria Check out Figure 18.8!!
Endospores are able to survive long periods of time.

16. Survival of Bacteria
If the environment changes and bacteria are not well adapted to the new conditions, what might happen?
Mutations:
If the conditions are harsh, bacteria might all die out.
Bacteria reproduce quickly  large populations rapidly
Genetic mutations can take place and help bacteria survive in changing environment.
Those that have an advantageous mutation can survive and reproduce.
How do you evaluate these mutations of bacteria
from the human point of view?

17. Ecology of Bacteria Do most types of bacteria cause disease?
Most bacteria do not cause disease in humans, other animals and plants.
Many are beneficial:
Recycle nutrients
Protect the body
Produce food and
medicines etc.

18. Ecology of Bacteria
Nitrogen cycle:
Normal flora:
Foods and medicines:

19. Ecology of Bacteria Disease causing bacteria:
Only a small percentage of bacteria cause disease.
Check out Table 18.1!!
Bacteria can cause disease by:
Multiplying quickly at the site of infection
Secreting a toxin or other
substances that might cause harm
Assignment: Pick a disease caused
by a type of bacteria. Research the
bacteria, the causes, symptoms and
prevention method of the disease.