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2) Introductory Microbiology COPY > Microbial Growth > Flashcards

Microbial Growth Flashcards

1
Q

What are organic molecules that a microorganism needs for growth but cannot synthesize by itself?

A

Vitamins, amino acids, purines, pyrimidines

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2
Q

Which micronutrient is limiting in nature? What is the consequence?

A
  • Iron

- Competition for iron is fierce

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3
Q

What is the function of iron in microorganisms?

A

Key component of many enzymes involved in respiration and photosynthesis

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4
Q

Differentiate the ferrous and ferric forms of iron.

A

Ferrous: soluble, Fe2+, anoxic conditions

- Ferric: insoluble, Fe3+, oxic

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5
Q

How is iron in anoxic conditions?

A
  • Ferrous, soluble, Fe2+

- Can be imported by the usual transporter

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6
Q

How is iron in oxic conditions?

A
  • Ferric, insoluble, Fe3+
  • Will precipitate, cannot use a transporter
  • Needs siderophore
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7
Q

What is the role of siderophore?

A
  • Soluble molecule that acts as a shuttle for a microorganism to acquire insoluble (Fe3+, ferric) iron
  • Microorganisms can use siderophores to steal iron from bacteria
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8
Q

What is the growth of a population?

A

Increased number of cells or biomass

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9
Q

How do most procaryotes multiply?

A

By binary fission

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10
Q

What is binary fission?

A

The cell grows in size until it forms a partition (septum) that constricts the cell into 2 daughter cells

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11
Q

How are the two daughter cells created by binary fission similar?

A

Each daugther will receive one copy of the chromosome, sufficient ribosomes, macromolecules, monomers, and other molecules to exist as an independent cell

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12
Q

What synthesis does cell division require?

A
  • Requires synthesis of new cell wall material

- Also, destruction of the cell wall by autolysins (enzyme)

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13
Q

What allows peptidoglycan subunits to be exported across the cytoplasmic membrane?

A

Bactoprenol (hydrophobic molecule)

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14
Q

Where does the cut happen in cell division?

A
  • In the middle

- At the FtsZ ring

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15
Q

How does cell division occur?

A
  • At the division ring (FtsZ ring), autolysins create some gaps in the peptidoglycan
  • Autolysins creates some gaps in the peptidoglycan, which allows the rearrangement of the peptidoglycan and the synthesis of a new cell wall
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16
Q

What are wall bands?

A

Scars between old and new peptidoglycan

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17
Q

What kind of organism has a similar cell division mechanism?

A

Archaea with a cell wall

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18
Q

What is the purpose of selective medium?

A

Will select for the growth of certain microorganisms

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19
Q

Why is MacConkey selective?

A

Because of the bile salts

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20
Q

Why is MacConkey differential?

A

Because of the pH indicator that indicates different colours based on the metabolic pathways

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21
Q

What do the bile salts in MacConkey inhibit?

A
  • Inhibits the growth of bacteria that are NOT enteric pathogens (live in the intestine)
  • Many Gram + are inhibited
  • Gram- will still grow
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22
Q

What colours will the two different metabolic pathways produce in MacConkey?

A
  • Lactose -> glucose and galactose; lactose fermenters will be pink, produces lactic acid; the glucose that undergoes the glycolytic pathway will also produce lactic acid
  • Lactose negative will not turn pink
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23
Q

What is the MacConkey like for E. coli?

A

Forms dark pink colonies with bile precipitate (right side is very pink, very acidic)

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24
Q

Why is the Mannitol-Salt agar selective?

A

Because of the high NaCl

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25
Q

Why is the Mannitol-Salt agar differential?

A

Because of the mannitol and the pH indicator

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26
Q

What does the high NaCl in the mannitol-salt agar inhibit?

A

Inhibits most Gram - and many Gram +

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27
Q

What is the Mannitol-Salt agar used for? Why?

A
  • Used for the isolation or detection of Staphylococcus

- Since it is able to resist high concentrations of salt

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28
Q

How do microorganisms react to mannitol differently in the mannitol-salt agar?

A
  • If they can ferment mannitol, they will bring the pH down; which turns the plate yellow
  • If they are mannitol negative (do not ferment), they will look like the plate
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29
Q

Is staphylococcus mannitol positive or negative?

A
  • Positive
  • Aureus is damaging, causes disease
  • Epidermidis is normal
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30
Q

What are the two methods to measure viable counts?

A
  • Speed-plate method: colonies onto agar (surface colonies)

- Pour-plate method: agar is added after (subsurface and surface colony)

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31
Q

What are viable counts?

A

Measuring culturable bacteria (alive)

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32
Q

How many colonies does each bacteria form?

A

One

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33
Q

What is the equation for CFU?

A 
CFU = (Nb of colonies) / (Dilution x Volume)
CFU = Plate count x Dilution factor
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34
Q

What kind of cells do microscopic counts measure?

A
  • ALL cells

- Dead, alive, and cells that cannot be grown in a lab

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35
Q

What are microscopic counts often used for?

A

Yeast cells since they are bigger and easy to see in a microscope

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36
Q

What is the advantage of microscopic counts? What is the disadvantage?

A

Advantage: fast, no need to wait for bacteria to grow
Disadvantage: small cells may be missed, and motile cells are hard to count (must be immobilized)

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37
Q

In the Petroff-Hauser Chamber, the space under the coverslip is a fixed ________

A

volume

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38
Q

How can you know the number of cells from the Petroff-Hauser Chamber?

A

Because you have a fixed volume, you can count the number of cells and then extrapolate the total number of cells in the sample

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39
Q

What is the disadvantage of the Petroff-Hauser Chamber? How can this be overcome?

A
  • Does not differentiate viable and dead cells

- Viability staining

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40
Q

What is viability staining? What is the problem?

A
  • Differentiates dead (red) and live (green) cells

- Difficult to differentiate very small or motile cells

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41
Q

What is flow cytometry? What is it best used for?

A
  • Counts cells in an automated fashion
  • Capillary allows cells to flow in a single line
  • A laser will count the number of cells
  • Best at counting big cells (protozoan, yeast, mammalian cells)
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42
Q

How can you detect the difference between live and dead cells in flow citometry?

A
  • The laser can detect differences in color

- Must use viability staining

43
Q

What does turbidimetry measure?

A

Measures the contribution of alive and dead cells to turbidity

44
Q

What is turbidimetry affected by?

A

By the behavior of cells, such as clumping and attachment to surfaces

45
Q

How does turbidity change with time? Why?

A
  • As the culture grows, turbidity (opaque/cloudy) increases with time
  • Since there are more cells in the sample, which block light
46
Q

What determines the turbidity in the machine?

A

The spectrophotometer will determine the amount of light blocked by the culture (absorbed), which is proportional to the number of cells

47
Q

What is the optical density? What is it affected by? Why is it not reliable?

A
  • Amount of light blocked by a culture
  • Affected by cell size, shape, composition, cell inclusions
  • Not reliable since it does not give a true number
48
Q

What is generation time?

A

Time needed for the population to double, due to binary fission

49
Q

How do microorganism populations grow when the conditions are right?

A

When the conditions are right, microorganisms can grow exponentially, and the population doubles at a constant rate

50
Q

What is the equation to determine the number of cells from the number of generation?

A

N = (N0)2^n

  • N is the number of cells
  • N0 is the number of cells initially
  • n is the number of generation
51
Q

What is the equation for generation time?

A

g = t/n

  • g is the generation time
  • t is the number
  • n is the number of generation
52
Q

If you inoculate aerobic bacteria in a tube, which step must be used?

A

Shake the culture to add oxygen

53
Q

What is the lag phase?

A
  • Time needed by the bacteria to adjust to the new condition (slow growth)
54
Q

What is the exponential phase?

A

Doubling of the population at a constant rate when conditions are optimal

55
Q

What is the stationary phase?

A
  • Limiting nutrients are depleted or accumulation of waste product that inhibits growth
  • Growth is stopped; no measurable growth (viable count and turbidity stay the same)
56
Q

What is the death phase?

A
  • Cells start to die
  • Metabolism stops
  • Also an exponential function
57
Q

How does turbidity change during the death phase?

A

Decreases because cells start to degenerate

58
Q

Do bacteria grow in a batch culture in real life?

A

No, they grow in continuous cultures (open systems)

59
Q

What are the conditions of an open system?

A
  • Constant supply of nutrients and diffusion of waste
  • Competition with other microorganisms
  • Predation
  • Changing environmental conditions
60
Q

Over time, what do environmental systems reach?

A

An equilibrium: division rate = death rate

61
Q

What can be used in a laboratory to keep microorganisms in a constant growth rate?

A

Chemostats

62
Q

What are the two parameters of a chemostat?

A

1) Concentration of a limiting nutrient

2) Dilution rate

63
Q

How does reaching the first nutrient concentration affect the chemostat’s rate and yield?

A
  • The rate and yield increases; grows at almost max speed

- At some point, there is no more limiting nutrient and growth stops (population will be maintained, not increased)

64
Q

Will the yield be affected by going to the second nutrient concentration? What about the speed?

A
  • The yield will increase

- The speed will not increase since max speed was reached

65
Q

What are the two factors that affect the concentration of a limiting nutrient in a chemostat?

A
  • Fresh medium

- Aeration

66
Q

What happens if you add fresh medium to a tank, and do not have an output?

A

It will overflow

67
Q

What are the effects of increasing the dilution rate?

A
  • Increases the input of nutrient/unit time

- Increases the removal of waste and biomass per unit of time

68
Q

What is the doubling time?

A

1/growth rate

69
Q

At steady state, how does the bacterial concentration (with increasing growth rate) change when dilution increases?

A
  • Does not increase because increasing the dilution increases removal
  • Growth rate = removal
70
Q

What happens if: removal > growth

A

Bacteria do not have time to reproduce, and they will decrease

71
Q

What happens if: removal < growth

A

Bacteria will have time to reproduce, and they will increase

72
Q

What are some factors affecting growth in nature?

A

Temperature, Nutrients, pH, Osmolality, Oxygen, Pressure, Radiation (visible light, UV light)

73
Q

What are extremophiles?

A

Microorganisms that grow preferentially under extreme conditions

74
Q

What is the temperature range for most microorganisms?

A

Typically 25-40oC around the optimal temperature

75
Q

What are psychotolerant organisms?

A

Organisms that can grow at 0oC, but have an optima around 20-40oC

76
Q

What are the consequences of microorganisms growing at optimal temperature?

A
  • Temperature at which they grow the fastest
  • Enzymatic reactions occur at optimum rate
  • Membrane is perfectly fluid
77
Q

What happens to microorganisms if the temperature is too low?

A

Membrane gelling: transport processes so slow that growth cannot occur

78
Q

What happens to microorganisms if the temperature is too high?

A

Protein denaturation: collapse of the cytoplasmic membrane; thermal lysis

79
Q

What are psychrophiles, mesophiles, thermophiles, and hyperthermophiles?

A
  • Psychrophile (0-10oC)
  • Mesophile (10-50oC)
  • Thermophile (40-70oC)
  • Hyperthermophile (70-110oC)
80
Q

What are the 5 adaptations to cold temperatures?

A
  • Changes in protein structure and sequence so the enzymes are active at low temperature
  • Transport across the membrane functions optimally at low temperature
  • Requires modification of the cytoplasmic membrane so it stays fluid at low temperatures
  • Cold-shock proteins which help keep proteins active
  • Cryoprotectants: antifreeze proteins, glycerol
81
Q

What are the functions of cryprotectants?

A

Help prevent the formation of ice crystals that can puncture the cytoplasmic membrane

82
Q

Do cold temperatures kill microorganisms?

A

No, ice crystals do

83
Q

Which microorganism grows at refrigerator temperatures?

A

Listeria

84
Q

Which microorganisms grow best at high pressures?

A

Barophilic

85
Q

What are the 5 adaptations to high temperatures?

A
  • Changes in protein sequence so the enzymes are not denatured by the high temperature and can stay active. These enzymes are heat-stable
  • Transport across the membrane functions optimally at high temperature
  • Requires modification of the cytoplasmic membrane so it remains stable at high temperatures
  • Heat-shock proteins, which help keep proteins in the active conformation
  • Protection mechanisms to ensure stability of DNA (GC rich)
86
Q

Do hot temperatures kill microorganisms?

A

Yes, through thermal lysis

87
Q

Can endospores grow at high temperatures?

A

NO, they can survive though but they are not metabolically active

88
Q

What are neutrophiles, acidophiles, and alkalinophiles?

A
  • Neutrophiles: pH 5.5-8
  • Acidophiles: pH below 5.5
  • Alkalinophiles: pH above 8
89
Q

What are the 3 adaptations to low pH?

A
  • Changes of the cytoplasmic membrane to resist high concentration of protons
  • The membrane usually requires high concentration of protons for stability
  • Bacteria lyse at higher pH, because the membrane becomes unstable
90
Q

What are the 3 adaptations to high pH?

A
  • Changes of the cytoplasmic membrane to resist low concentration of protons
  • Use of Na+ gradient for transport and motility (low concentration of protons outside, PMF is hard to maintain)
  • Keep the electron transport chain close to the ATPase, so protons that are pumped out do not diffuse away
91
Q

How does the ideal pH of DNA and RNA differ?

A
  • DNA is acid-labile (degraded by acid)

- RNA is alkali-labile (degraded by alkali)

92
Q

What are used in growth mediums to keep pH steady? Why?

A
  • Buffers

- Because bacterial waste tends to affect pH

93
Q

Microorganisms that can grow at high concentrations are called _________

A

halophiles

94
Q

What is the difference between facultative and obligate aerobes?

A
  • Facultative: grow best with O2, although not needed

- Obligate: need O2

95
Q

How are toxic forms of oxygen produced?

A
  • Aerobic respiration: O2 is reduced to H2O

- Oxygenic photosynthesis: H2O is oxidized to O2

96
Q

What proteins can reduce O2 to toxic forms of oxygen?

A

Flavoproteins, quinone, and iron-sulfur proteins

97
Q

What are the effects of toxic forms of oxygen in a cell?

A
  • Oxidize cell components, stopping key metabolic pathways
  • Create reactive oxygen species (superoxide, hydrogen peroxide)
  • Will steal electrons, oxidizing components and destroying structures
98
Q

How do aerobes and facultative aerobes resist toxic forms of oxygen?

A

Have catalase and superoxide dismutase to destroy ROS

99
Q

Why aren’t aerobes resistant to toxic forms of oxygen?

A
  • Lack the enzyme, or the enzyme activity is not sufficient to allow growth under oxic conditions
  • However, it may be sufficient to survive
100
Q

How does the DNA of microorganisms change at high temperatures?

A

GC rich

101
Q

How does the population change if you increase dilution rate at equilibrium?

A

It stays the same (go see lecture after 1 h)

102
Q

What are 4 ways to measure microbial growth?

A

1) Microscopic counts
2) Spread plate
3) Turbidity
4) Flow cytometry

103
Q

How can you detect live cells without staining?

A
  • Spread plate

- Microscopic and cytometry can be used but only with staining

2) Introductory Microbiology COPY (24 decks)

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