Microbiology Lecture Notes October 5

October 5, 2009
4. Phases of bacterial growth curve (in culture… not in nature) assuming pure culture of bacteria
a. Lag phase
i. Due to the math of the growth
ii. Take s awhile to go from having few bacteria to having a lot
iii. Bacterial cell division getting started
iv. Generation times not as rapid as will be during Exponential Phase (b)
v. Bacteria are making:
1. ATP
2. Cell envelope components
3. Enzymes: DNA polymerase; Ftsz;
4. Need a lot of things before they can actually get cell division started
b. Exponential phase (log phase)
i. During this phase, generation time is shortest, nutrients are abundant
1. So bacteria easily able to make all components needed for cell division
c. Stationary phase
i. Growth has stopped
ii. Number of deaths may = number of new bacteria
iii. Population is not growing
iv. Bacteria starting to run out of nutrients and space
1. Much less able to make all the enzymes that are needed to make the bacteria divide ; also, lack of food  some bacteria dying
d. Death phase
i. # of new bacteria vastly outnumbered by # bacteria dying
ii. Cell division has essentially stopped b/c nearly out of food to conserve the food
iii. Because of out of food, living bacteria have nothing to eat either so they start to die
iv. Suicide at high population densities common among bacteria
1. Bacteria cells have receptors on the outside of them; signaling molecules secreted by the bacterium and diffuse down the concentration gradient
2. At some point there will be no where for the signaling molecules to go/diffuse to
a. Then they stick to the receptor and the bacterium is signaled to kill it self
b. It’s the bacteria’s own enzyme that kills them
5. Generation time = 0.301 (t-t0)/(log10N-log10N0) (don’t need to know)
6. Can T4 Phages infect human cells
a. Human cells do not have proper receptors for the Phages
7. Can E.Coli become resistant to T4 Phages

Amy Blass

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