Lecture 9 Flashcards
What does growth refer to?
increase in cell number and NOT an increase in cell size
How does growth work? (4)
1) Cells grow to a critical mass
2) Divide
3) Repeat
4) Growth is exponential 2^n
What factors regulate growth? (3)
1) nutrient availability
2) environmental conditions
3) generation time
What are the chemical requirements for growth? (3)
1) water
2) elements: carbon, hydrogen, oxygen, nitrogen, sulfur, etc
3) organic for heterotrophs: glucose
What are psychrophiles?
microbes that love the cold
What are mesophiles?
microbes that love moderate temperatures
What are thermophiles?
heat loving microbes
What does facultative?
has a range
What is obilgate?
needs a specific condition
What is death above the maximum temp due to?
enzyme inactivation
Which is the most common temperatures for microbes?
mesophiles
At what temperature do most microbes stop growing?
40 F or 5 C
What are obligate aerobes?
require oxygen
What are facultative anaerobes?
use oxygen but can also grow without it
What are obligate anaerobes?
die in the presence of oxygen
What pH do most bacteria grow between?
6.5 pH and 7.5 pH
What is considered an acid? what benefits do acids have?
below 4, can preserve food bc prevents bacterial growth
What are acidophiles?
live at low pH
What are the phases of microbial growth?
1) lag phase
2) log phase
3) stationary phase
4) death phase
What happens in the lag phase?
making new enzymes in response to new medium (aka “LOOK! FOOD!”)
What happens in the log phase?
exponential growth (aka ”EAT ALL THE FOOD”)
—Desired for production of products
—Most sensitive to drugs and radiation during this period, ex) antibioctics
What happens in the stationary phase?
plateaued growth (aka “more food please?”)
—nutrients becoming limiting or waste products becoming toxic
—death rate = division rate
What happens in the death phase?
death exceeds division
How do you measure microbial growth in the lab? (5)
1) Fill flask with growth media
2) Sterilize to kill any contaminating microbes
3) Aseptically add a very small amount of bacteria
4) Place the flask in a shaking incubator at 37°C (if aerobic!!)
5) Return the next day and the culture is cloudy!
What is turbidity?
common way to measure microbial growth,
Measure optical density (OD) using a spectrophotometer
What does a higher OD mean?
less light got through and more bacteria are present (standards relate bacterial # or colony forming units to OD)
Can OD measure viability? why or why not?
no, bc OD measures dead and live cells
How do you do a CFU? (colony forming units) (4)
1) In a CFU assay samples are taken at each time point and plated on an agar plate
2) These plates are incubated until visible colonies form
3) The colonies are counted – each colony was originally founded by a single bacterium, a colony forming unit
4) Only live bacteria in the culture can form colonies
What is cytometry?
sorts live and dead cells
How does cytometry work? (5)
1) First, treat cells with a live/dead stain
2) Propidium iodide (red) is taken up by dead cells
3) SYTO 9 (green) binds to live cells
4) Samples pass one at a time through a laser beam in the cytometer
5) Wavelength of light emitted reveals if stained green (live) or red (dead)
How do you cell calculate growth?
2^n
n = number of generations
How do you calculate number of cells (N)?
N=2n(N0) or logN = n(log2) + logN0
How do you calculate the number of generations? (n)
n = (logN–logN0)/0.301
How do you calculate generation time?
g=t/n
t = amount of time between the start and finish
n = number of generations
How can you differentiate fast versus slow growth?
Fast growth requires more protein synthesis, so ribosomes and RNA increase drastically
What is binary fission?
cell division following enlargement of a cell to twice its minimum size
What is generation time?
time required for microbial cells to double in number
What are Fts proteins?
filamentous temperature-sensitive
Essential for cell division in all prokaryotes
What is FtsZ?
forms a ring around center of cell (Z-ring)
What is ZipA?
anchors FtsZ ring to cytoplasmic membrane
What is FtsA?
helps connect FtsZ ring to the membrane and recruits other proteins
When does DNA replicate?
before the FtsZ ring forms
What is FtsK?
mediates separation of chromosomes to daughter cells
How were the Fts proteins discovered? (3)
1) Researchers identified mutants of E. coli that grew normally at either 30°C or 42°C, but could only divide at 30°C
2) At 42°C the mutants, being unable to divide, grew as filaments rather than as individual cells
3) Because of their filamentous temperature-sensitive phenotype when disrupted the genes were named filamentous temperature sensitive or fts
What is a divisome? made of?
cell division apparatus, made of FtsZ, ZipA, FtsA
What is FtsZ closely related to?
eukaryotic tubulin
What does FtsZ self assemble into?
filament
What does the min system control?
where the septum forms
What does MinC do?
depolymerizes FtsZ filaments
What does MinCD do?
complex oscillates between the cell poles due to the position of MinE
prevents Z ring
not localized to the poles
What does MinE ring do?
travels between the ¼ and ¾ position of the cell and depolymerizes
How was the Min system discovered? (4)
1) Researchers made a bunch of mutant E. coli strains
2) Found that some of them divided abnormally at the ends and not in the middle
3) Produced “minicells” devoid of chromosomes
4) Named the genes disrupted in these mutants min for minicell formers
