Lecture 9

Question 1

What does growth refer to?

Answer 1

increase in cell number and NOT an increase in cell size

Question 2

How does growth work? (4)

Answer 2

1) Cells grow to a critical mass
2) Divide
3) Repeat
4) Growth is exponential 2^n

Question 3

What factors regulate growth? (3)

Answer 3

1) nutrient availability
2) environmental conditions
3) generation time

Question 4

What are the chemical requirements for growth? (3)

Answer 4

1) water
2) elements: carbon, hydrogen, oxygen, nitrogen, sulfur, etc
3) organic for heterotrophs: glucose

Question 5

What are psychrophiles?

Answer 5

microbes that love the cold

Question 6

What are mesophiles?

Answer 6

microbes that love moderate temperatures

Question 7

What are thermophiles?

Answer 7

heat loving microbes

Question 8

What does facultative?

Answer 8

has a range

Question 9

What is obilgate?

Answer 9

needs a specific condition

Question 10

What is death above the maximum temp due to?

Answer 10

enzyme inactivation

Question 11

Which is the most common temperatures for microbes?

Answer 11

mesophiles

Question 12

At what temperature do most microbes stop growing?

Answer 12

40 F or 5 C

Question 13

What are obligate aerobes?

Answer 13

require oxygen

Question 14

What are facultative anaerobes?

Answer 14

use oxygen but can also grow without it

Question 15

What are obligate anaerobes?

Answer 15

die in the presence of oxygen

Question 16

What pH do most bacteria grow between?

Answer 16

6.5 pH and 7.5 pH

Question 17

What is considered an acid? what benefits do acids have?

Answer 17

below 4, can preserve food bc prevents bacterial growth

Question 18

What are acidophiles?

Answer 18

live at low pH

Question 19

What are the phases of microbial growth?

Answer 19

1) lag phase
2) log phase
3) stationary phase
4) death phase

Question 20

What happens in the lag phase?

Answer 20

making new enzymes in response to new medium (aka “LOOK! FOOD!”)

Question 21

What happens in the log phase?

Answer 21

exponential growth (aka ”EAT ALL THE FOOD”)
—Desired for production of products
—Most sensitive to drugs and radiation during this period, ex) antibioctics

Question 22

What happens in the stationary phase?

Answer 22

plateaued growth (aka “more food please?”)
—nutrients becoming limiting or waste products becoming toxic
—death rate = division rate

Question 23

What happens in the death phase?

Answer 23

death exceeds division

Question 24

How do you measure microbial growth in the lab? (5)

Answer 24

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!

Question 25

What is turbidity?

Answer 25

common way to measure microbial growth, Measure optical density (OD) using a spectrophotometer

Question 26

What does a higher OD mean?

Answer 26

less light got through and more bacteria are present (standards relate bacterial # or colony forming units to OD)

Question 27

Can OD measure viability? why or why not?

Answer 27

no, bc OD measures dead and live cells

Question 28

How do you do a CFU? (colony forming units) (4)

Answer 28

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

Question 29

What is cytometry?

Answer 29

sorts live and dead cells

Question 30

How does cytometry work? (5)

Answer 30

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)

Question 31

How do you cell calculate growth?

Answer 31

2^n n = number of generations

Question 32

How do you calculate number of cells (N)?

Answer 32

N=2n(N0) or logN = n(log2) + logN0

Question 33

How do you calculate the number of generations? (n)

Answer 33

n = (logN–logN0)/0.301

Question 34

How do you calculate generation time?

Answer 34

g=t/n t = amount of time between the start and finish n = number of generations

Question 35

How can you differentiate fast versus slow growth?

Answer 35

Fast growth requires more protein synthesis, so ribosomes and RNA increase drastically

Question 36

What is binary fission?

Answer 36

cell division following enlargement of a cell to twice its minimum size

Question 37

What is generation time?

Answer 37

time required for microbial cells to double in number

Question 38

What are Fts proteins?

Answer 38

filamentous temperature-sensitive Essential for cell division in all prokaryotes

Question 39

What is FtsZ?

Answer 39

forms a ring around center of cell (Z-ring)

Question 40

What is ZipA?

Answer 40

anchors FtsZ ring to cytoplasmic membrane

Question 41

What is FtsA?

Answer 41

helps connect FtsZ ring to the membrane and recruits other proteins

Question 42

When does DNA replicate?

Answer 42

before the FtsZ ring forms

Question 43

What is FtsK?

Answer 43

mediates separation of chromosomes to daughter cells

Question 44

How were the Fts proteins discovered? (3)

Answer 44

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

Question 45

What is a divisome? made of?

Answer 45

cell division apparatus, made of FtsZ, ZipA, FtsA

Question 46

What is FtsZ closely related to?

Answer 46

eukaryotic tubulin

Question 47

What does FtsZ self assemble into?

Answer 47

filament

Question 48

What does the min system control?

Answer 48

where the septum forms

Question 49

What does MinC do?

Answer 49

depolymerizes FtsZ filaments

Question 50

What does MinCD do?

Answer 50

complex oscillates between the cell poles due to the position of MinE prevents Z ring not localized to the poles

Question 51

What does MinE ring do?

Answer 51

travels between the ¼ and ¾ position of the cell and depolymerizes

Question 52

How was the Min system discovered? (4)

Answer 52

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