Prokaryotes
Or 100 Trillion Friends That
You Didn’t Know You Had
The Human Microbiome


We are actually a giant ecosystem of microbes
Prokaryotes comprise between 1-3% of the mass
of a human body
- up to 6lbs of a 200 lb person can be microbes
Classification: Some Old,
Some New


Biologists have typically classified living
things into 5 large groups called kingdoms
- Monera, Protista, Fungi, Plantae &
Animalia
Then biologists discovered organisms
called Archea – they are prokaryotic
organisms but aren’t bacteria.
- What to do?
The Challenge of Archea



Archea present a problem, they
are prokaryotes
– They have no nucleus or organelles
They also share traits with eukaryotes
- similarities in DNA and synthesis
They have traits unique to themselves
- cell membrane lipids, ability to
survive extremely high temperature
a
Enter the Domain System of
Classification

Scientists divided living things into 3
Supergroups called domains these consist of
Bacteria, Archea and Eukarya
Archea can be Extremophiles

Some species of archea can be found in
environments so extreme, that nothing
else lives there- extreme temps, extreme
pH, extremely salty etc…
Bacteria



Earth’s oldest life forms
– between 3.5 and 3.8 billion years old
Most abundant life form – up to 2.5 billion
individual bacteria in 1 gram of fertile soil
Very adaptable – found in all of Earth’s
ecosystems
Bacteria Characteristics






Unicellular
Circular DNA
No organelles
1/10th the size of eukaryotic cells
Flagella-long hair-like structure used for
movement
Reproduce asexually –Binary Fission
Bacterial Shapes

3 main shapes
- coccus – sphere
- bacillus – rods
- spirillum - spiral
Bacterial Characteristics

Metabolic diversity –
Bacteria can produce
energy in a variety of circumstances
autotroph – (self-feeding) – some bacteria can
produce their own food
- some use photosynthesis – get energy from
light
- some use chemosynthesis – get energy from
chemicals
Heterotroph - (other feeding) – many bacteria
are unable to produce their own
food and are required to eat other
things
Bacterial Characteristics:
Metabolic diversity continued
obligate aerobe – like us these bacteria need oxygen
obligate anaerobe - these bacteria need to be in an oxygen
free environment – human gut
facultative anaerobe – these bacteria can live in either an
oxygen or oxygen free environment
Bacterial Structure
Cell Wall
Cell Membrane
Pilus
chromosome
nucleoid
capsule
plasmid cytoplasm
flagellum
ribosome
Bacterial Structure: Cell Wall


Made of peptidoglycan – a combination of protein and
polysaccharides
Some bacteria called Gram negative bacteria have an additional
layer of membrane that contains lipopolysaccharide
- this extra layer inhibits the uptake of antibiotics – protecting
the bacteria
cell wall
cell
membrane
cell
membrane
lipopolysaccharide
cell wall
Outer membrane
Gram + vs. Gram The type of cell wall is used by
doctors to help diagnose disease
The bacteria are stained with a
special stain called Gram stain
Bacteria without the extra membrane,
appear purple. These are Gram positive
(Gram +) bacteria
Absorb stain appear purple
Bacteria with the extra membrane
appear pink. These are Gram negative
( Gram -) bacteria
Don’t absorb stain appear
pink
Bacterial Structure continued





Pili – hairlike structures usually found
in Gram neg. bacteria. Help the
bacteria stick to surfaces.
Also forms conjugation bridge
Chromosome – a single loop of DNA
that is folded on itself
- controls the cell’s function
Nucleoid – the region of the cytoplasm
where the DNA is found
Plasmid – an accessory loop of DNA – small contains only a few
genes - can be responsible for: conjugation, antibiotic
resistance, unique metabolic properties – like the ability to
use hydrocarbons
Capsule – found outside some bacteria stores nutrients and protects
the bacteria from changing environmental conditions
Reproduction - Binary Fission
Bacterial cells undergoing binary fission
Reproduction - Binary Fission

Asexual reproduction
- offspring are genetically
identical to parent – no
new genetic combinations
- under ideal conditions
can occur every 20 min
- creates large numbers
of bacteria in a short
time


Each spot represents
a single bacterial
cell that reproduced
by binary fission to
produce millions of
genetically identical
cells.
Genetically identical,
good or bad?
Exchanging Genetic Information


Bacterial cells need to be able to exchange genetic
information
- creates new genetic combinations which increases the
ability of the bacteria to survive
Bacteria have 3 methods for exchanging DNA
-Transduction – viruses carry DNA from one bacterial
cell to another
-Transformation – bacteria can absorb “naked” DNA
released by dead bacteria from
the environment
-
Conjugation – two bacteria join at a conjugation
bridge, one bacteria passes on a
copy of its plasmid or chromosome
Exchanging Genetic Information
Transduction – DNA is carried from one
bacteria to another by a virus
Transformation: Bacteria absorb
“naked” DNA from the
environment
Conjugation
Conjugation-
one cell passes a copy of
its plasmid or chromosome to another
Donor Cell
Recipient
Cell
A special pilus forms
a connection called
a conjugation bridge
between 2 bacterial
cells
Plasmid
Conjugation bridge
The donor cell
copies its plasmid
or chromosome and
passes the copy
through the
conjugation bridge
Cells separate
Bacteria Play Important Roles in
Ecosystems

Decomposers
– recycle dead organisms releasing their
nutrients back to the environment for
use by other organisms – SPONCH
Without decomposers,
the elements on earth
would have remained
locked up in dead
organisms and life
would have ceased
Bacterial Roles: Nitrogen Fixation

some bacteria contain enzymes which allow them to
convert (or fix) nitrogen from the air into a useable form
- they are nitrogen fixing bacteria
Why do living things use nitrogen?
Bacterial Roles: Producers

In some ecosystems
chemosynthetic and
photosynthetic bacteria
serve as the basis of
the food chain
– chemosynthetic bacteria in deep ocean vents
convert hydrogen sulfide (H2S) gas into energy
- cyanobacteria are photosynthetic bacteria
which act as producers in many aquatic
ecosystems
Bacterial Roles: Symbiotic Bacteria
Many bacteria live in or on other organisms
(including humans) and aid their host
- some live in the gut of herbivores helping to
digest cellulose
- bacteria in the gut of humans
aid digestion and produce
vitamins
- bacteria on skin and in body
openings help prevent infection
by harmful organisms
Bacterial Roles:

Pathogenic Bacteria
Pathogens are organisms that cause disease
- only a small portion of bacteria are pathogens
- most bacteria diseases are caused by toxins
released by the bacteria
- these toxins:
- poison cells and damage tissue
- interfere with cell signaling
- over-stimulate cells causing them to
malfunction
Pathogenic Bacteria: Biofilms

Some bacteria can form a biofilm – a matrix
made of polysaccharide
- once formed, the matrix traps other bacteria
- the biofilm protects the bacteria, making it
hard to kill them
Antibiotics



Antibiotics are chemicals which either kill bacteria or
prevent their growth and reproduction
Bacteria and other microbes produce antibiotics to
reduce competition from other organisms
Penicillin was the first to be use to fight disease
- discovered accidently by Alexander Fleming in 1928


Two scientists Walter Florey and Ernst Chain determined
how to use penicillin to
treat disease in 1939.
The discovery of
antibiotics revolutionized
the treatment
of disease
Antibiotic Action


Antibiotics effect bacteria, but not eukaryotic cells
Antibiotics attack bacteria in 5 ways
- some damage the cell walls or prevent new cell wall from forming
- some damage the cell membrane
- some prevent protein synthesis
- some prevent DNA from being copied
- some interfere with bacterial metabolism
Antibiotic Resistance


Some bacteria have developed a resistance to the effect
of some antibiotics
- the number of resistant bacteria is growing
The problem is increased by overuse and misuse of
antibiotics
- use of antibiotics to treat viral infections – antibiotics don’t effect
viruses
- the use of antibiotics in livestock (cattle, chickens, pigs)
antibiotics show up in the meat and milk
- people take the antibiotics until they feel better, but stop before all
of the bacteria are destroyed
- this kills the most susceptible bacteria, but leaves the more
resistant bacteria
Black Plague-Yersinia pestis
Syphilis--Treponema
pallidum/Bacterial
Mycobacterium leprae/Bacteria
Clostridium perfringes/Bacteria
Vocabulary
Microbiome
autotroph
heterotroph
peptidoglycan
plasmid
Gram Gram +
binary fission
conjugation
transduction
transformation
biofilm
Archea
pili
nucleoid
capsule
conjugation bridge
obligate aerobe
obligate anaerobe
facultative anaerobe
nitrogen fixing bacteria
cyanobacteria
pathogens