Microbiology Lecture Notes 10/12

October 12, 2009

b. Hydrostatic pressure/atmospheric pressure
c. Oxygen
i. Limiting factor for bacterial growth
ii. Our atmosphere on planet earth is about 20% oxygen
1. Toxic! Why is oxygen toxic?
a. Inhibits growth of many kinds of bacteria
b. Antioxidant is any material that “soaks up” free electrons
i. This helps prevent damage to DNA proteins caused by electrons bouncing around & breaking DNA strands/altering protein structure
2. Oxygen is very attracted to electrons so is very electronegative
a. If oxygen is present then a lot of electrons are attracted to it and the electrons bounce around and break stuff in the cell
b. So cell in environment w/ lots of oxygen is also in presence of lots of electrons
i. Electrons bounce around, break DNA, proteins
iii. Anaerobes
1. Cannot live in presence of ANY oxygen
2. Strict vs. facultative
3. Faculative:
a. can live with or without oxygen E. Coli
4. Strict:
a. C. Dificile cannot live in oxygen at all!!
b. Environments where they can live would be:
i. Bottom of the ocean possibly
ii. Deep in the soil
iii. Intestines
iv. Vagina
v. Many are in the human body
iv. Aerobes
1. Oxygen is the terminal electron acceptor
2. Oxygen is very attracted to electrons
3. Have to have specific mechanisms to deal w/ all the problems oxygen causes by attracting electrons and therefore destroying their DNA proteins
4. Environment cells (e.g. ours, ALL bacterial cells that live in normal oxygen ~20%), must have mechanisms for fixing DNA & protein damage caused by e-‘s and oxygen
5. Like our cells; require oxygen to grow
a. Use aerobic respiration as their primary means for generating ATP
b. Use identical ATP-generating mechanisms (w/ oxygen as terminal electron acceptor) as our mitochondria do
c. Cannot live in anaerobic environments
d. Most skin normal flora are aerobes
i. Staphylococci (gm +)
v. Other atmospheric requirements
1. Microaerophiles
a. Require a little bit of oxygen (5% or less) to grow but die w/ more oxygen than that
b. If very much is there at all they cannot deal w/ the damage done to their DNA
2. Capnophiles
a. Bacteria that must have some amount of oxygen to grow and have 5-10% of carbon dioxide to grow
i. Lungs are an example of an environment
b. Almost all pneumonia causing bacteria are an example
Why does oxygen inhibit the growth of many kinds of bacteria? Why do other kinds of bacteria (and your mitochondria) and oxygen?
d. Temperature
i. Psychrophiles
1. Bacteria that grow the best where it is very cold
2. ~-5C to about 10C
3. If any warmer than this they will die
a. Denatures proteins
4. Lots unsaturated fats in membrane
a. Better 4 u
b. Olive oil
c. Liquid at room temperature
d. More flexible at lower temperatures
e. Must have these so they ar flexible enough to divide
5. Little G&C, lots of A&T in DNA
ii. Mesophiles
1. Bacteria that grow best at ~20C-35C
2. All bacteria that live in/on our bodies
iii. Thermophiles & hyperthermophiles
1. Any bacteria that live the best at 60C
2. Hot enough to give a burn
3. Bacteria that live best at a little above 100C
4. Saturated fat in membrane
a. Butter
b. Stays solid at room temperature
c. Worries more about how to keep cell membrane together rather than if it is flexible
5. Lots of G&C and little A&T in DNA
iv. G and C have triple bond ant herefore more energy to break their bond and A and T have 2 bonds
v. G and C are more stable at higher temperatures and is why thermophiles and hyperthermophiles use more of these in DNA
e. pH
i. Acidophiles
1. Bacteria that live best at low pH (1.0-3.0)
2. Cause of stomach ulcers in H pylori
ii. Alkalophiles
1. Live best a high pH (10.0)
iii. Internal pH of cells is always 7 no matter what pH the environment they live in is
f. competition from other microbes; predation by phages and by other bacteria
Note: As long as there’s liquid water, some kind of prokaryote can thrive in practically any environment
Note: For bacteria to case disease in humans, that kind of bacteria must be able to grow in the human body
Do you have to worry about an epidemic caused by bacteria from Mars?

Amy Blass

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