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Introductory Microbiology > Microbial growth > Flashcards

Microbial growth Flashcards

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1
Q

6 essential elements for e.coli growth

A 
Carbon
Oxygen
Nitrogen
Hydrogen
Phosphorus
Selenium
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2
Q

Micronutrients for e.coli growth

A

Iron

Trace metals

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3
Q

What are growth factors

A

Vitamins, amino acids, purines, pyrimidines or other organic molecules that the microorganism need for growth but cannot synthesize by itself. Some growth factors are by-product or waste of another microorganism

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4
Q

From what sources can carbon be obtained for e.coli

A

CO2, organic compounds

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5
Q

From what sources can nitrogen be obtained for e.coli

A

NH3
NO3-
N2
organic nitrogen compounds (amino acids)

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6
Q

From what sources can hydrogen be obtained for e.coli

A

H2O

Organic compounds

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7
Q

From what sources can oxygen be obtained for e.coli

A

H2O
O2
organic compounds

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8
Q

From what sources can phosphorus be obtained for e.coli

A

PO4

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9
Q

From what sources can sulphur be obtained for e.coli

A

H2S
SO4
Organic S compounds (cysteine)
metal sulfide (FeS,CuS,ZnS,etc)

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10
Q

From what sources can potassium be obtained for e.coli

A

K+ in solution or various K salts

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11
Q

From what sources can magnesium be obtained for e.coli

A

Mg in solution or various Mg salts

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12
Q

From what sources can calcium be obtained for e.coli

A

Ca in solution or various Ca salts

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13
Q

From what sources can sodium be obtained for e.coli

A

Na in solution or various Na salts

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14
Q

What happens if bacteria do not have excess to iron

A

No electron transport chain

There is little Fe in the ocean, so cyanobacteria are not so active

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15
Q

What is the growth of population

A

Increase number of cells or biomass

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16
Q

How do most prokaryotic cells multiply

A

By binary fusion

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

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17
Q

What does each daughter cell receive when dividing?

A 
one copy of Chromosome
Sufficient ribosomes
Macromolecules
Monomers
And other molecules that will allow her to exist as an independent cell
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18
Q

What is the usual time for e.coli to divide

A

20 minutes

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19
Q

What does cell division require ( cell wall)

A

Synthesize of new cell wall material, but also requires its destruction by autolysins

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20
Q

What does bactoprenol do

A

It brings new peptidoglycan subunits across the cytoplasmic membrane

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21
Q

What enzymes incorporates new peptidoglycan subunits ?

A

Transpeptidases

Transglycosylases

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22
Q

What is formed at theseptum when cell is dividing

A

FtsZ ring

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23
Q

What does FtsZ ring do

A

It contracts and allows the cells to pinch off from each other in two different cells

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24
Q

What happens at FtsZ ring

A

Autolysins create some gaps in the peptidoglycan. This allows rearrangement of the peptidoglycan and synthesis of a new cell wall

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25
Q

What is a wall band

A

Scar between old and new peptidoglycan

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26
Q

What mechanism of cell division in Archea

A

Similar to bacteria

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27
Q

What is MacConkey medium

A

Selective medium

It has bile salts that inhibit growth of Gram+ bacteria, permissive for Gram negative enteric pathogen (e.coli)

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28
Q

Why MacConkey Agar is a differential media

A

It allows to distinguish between Lactose ferments (Pink) and Lactose non-ferments (colorless)

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29
Q

What reaction happens on MacConkey Agar and lactose

A

Lactose is a galactose +glucose
Glucose->glycolytic pathway->fermentation of lactate ( reduce pH)
The change of pH changes the color

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30
Q

What color do e.coli turn on MacConkey Agar

A

Dark pink because it is able of lactose fermentation

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31
Q

What kind of medium is Mannitol-salt and explain its action

A

Selective medium
High in NaCl: inhibits most Gram- and Gram+
Used for isolation or detection of Staphylococcus

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32
Q

Mannitol fermenters will show what result in Manitol-salt media

A

Yellow- manitol dermenters
Pink-manitol negative

Staphylococcus aureus is manitol +

Staphylococcus epidermidis-pink

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33
Q

Two different methods of creating agar sample with bacteria

A

Spread-plate method ( only on top)

Pour-plate method ( throughout the agar)

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34
Q

What is the number range for a reliable result?

A

Between 30-300 colonies

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35
Q

At what temperature do e.coli grow

A

37

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36
Q

What is the purpose of serial dilution

A

To get a viable count of such cultures, serial dilutions have to be made

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37
Q

The formula for CFU

A

Number of colonies (dilution plated* volume plated)

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38
Q

What is the advantage of microscopic counts vs serial dilution

A

In microscopic counts you can count dead bacteria as well as alive + no need to wait until bacteria grow

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39
Q

What is used for microscopic counts?

A

Counting chamber

40
Q

What is the disadvantage of microscopic counts

A

Small cells can be missed (magnification is not enough) , motile cells are hard to count and must be immobolized

41
Q

What is the work principle of flow cytometry

A

Every time a cell passes the laser it counts it, because the laser is interrupted

42
Q

Flow cytometry is better in counting what kind of cells

A

Big cells: protozoan,yeast,mammalian cells,etc.

43
Q

What is the advantage of flow cymmetry

A

Can be used to sort cells according to size, shape,labeling,etc.
Different types of cells or species can be labelled

44
Q

We use the dead to control to know what

A

Where the cells are dead.To define after at the test sample where the dead cells are. To establish this area

45
Q

The disadvantage of flow cytometry

A

Time consuming and expensive

46
Q

What is the usual method that is used to quantify bacteria in the lab

A

Turbidimetric method

47
Q

Explain the principle of Turbidimetric method

A

A light source that is broken into different wavelength of light through prisma( we can select any wavelength, but for bacteria 600 works the best). Then if there is a bacteria the light will be scattered and it won’t reach the spectrophotometer that will convert it to optical density

48
Q

What concentration should be used for Turbidimetric method

A

not too dense , so the the readings can be reliable (0.1 to 1 OD)

49
Q

Turbidimetric method measures both ___ and ___

A

Living and dead cells

50
Q

OD is affected by ___

A

Properties of cells: size, clumping,etc.

51
Q

What is the extra step that you need to do after Turbidimetric method

A

You need to make a relationship between OD and cell number( microscopy counts) and then the graph should be made

52
Q

What is generation time

A

Time needed for the population to double

53
Q

Generation time depends on ___

A

Growth medium and the conditions

54
Q

When the conditions are right, microorganisms can grow ___

A

Exponentially ( doubling at a constant rate)

55
Q

What is the formula for number of cells in some time

A

N(number of cells)=N0(number of cells initially)*2^n , where n is number of generation

56
Q

What is generation time

A

The time it takes for bacteria to double

57
Q

What is the formula for generation time

A

g=t/n

58
Q

When you make a graph cells/time , the steeper the line , then ___

A

The smaller the time when population doubles

59
Q

Why for bacteria growth in the lab Erlenmeyer flask is used

A

we like to put on the shaking table , do not splash and has a big air space , so the culture is kept aerated

60
Q

What are the usual growth phases of bacteria

A

Lag- when nothing happens and the culture is adjusting

Exponential growth- when the culture is doubling

Stationary - when the nutrients are run out or when the waist products accumulate , the growth rate is equal with the death rate

Death phase

61
Q

Dead bacteria do not contribute to ___

A

OD

62
Q

Two phases with exponential function

A

Exponential growth and death phase

63
Q

What medium mimics natural conditions the most

A

continuous culture

64
Q

What is the chemostat

A

Fresh medium: supply of limiting nutrients
Overflow: death of microorganism
It is used to keep microorganisms in a constant growth rate over a long period of time

65
Q

What are we changing with the chemostat

A

Dilution rate: at what rate there is an addition of fresh medium.

66
Q

What is important about the dilution rate

A

At very low rates and at very fast rates, it does not work very well, but in the middle we can achieve the steady state, where the bacterial population is the same

67
Q

Once equilibrium is reached, ____

A

Number of cells is constant; the growth rate equals the death rate ( washout)

68
Q

Most microbial species grow as

A

A mixed culture with other organisms

69
Q

Who are extremophiles

A

Microorganisms that grow preferentially under extreme conditions

70
Q

What happens at minimum, optimal and maxiumum temperatures

A

Minimum: membrane gelling; transport processes so slow that growth cannot occur

Optimum:enzymatic reactions occurring at maximal rate

Maximum: protein denaturation; collapse of the cytoplasmic membrane; thermal lysis

71
Q

Who are psychrotolerant

A

Organisms that can grow at 0 C but have optima around 20-40 C

72
Q

Who are psychrophiles

A

Optimum temperature 4 C, but they can grow less than 0

73
Q

Who are mesophiles

A

Grow around body temperatureto 39 C

74
Q

Who are thermophiles

A

Grow around 60 C

75
Q

Who are hyperthermophile

A

88 C or even 106 C

76
Q

What microorganisms grow at -15 C

A

Planococcus halocryophilus

77
Q

What really kills microorganisms in cold

A

Not the temperature, but ice crystals

78
Q

What are adaptations to cold temperatures

A
  • Changes in protein structure and sequence so the enzyme are active
  • Transport across the membrane functions optimally at low temperature
  • Requires modification of the cytoplasmic membrane to keep it fluid
  • Cold-shock protein which keep proteins active
79
Q

What are cryoprotectants

A

antifreeze proteins, like glycerol. They help prevent the formation of ice crystals that can puncture the cytoplasmic membrane . Glycerol should be present in the environment

80
Q

Microbial cultures are preserves at

A

-80 or -196 C in liquid nitrogen

81
Q

Who are barophillic bacteria

A

Grow best at high pressure

82
Q

Adaptations to high temperatures

A
  • Protein that are heat-stable
  • Transport against the membrane with optimal activity at high temperatures
  • Modifications of of the cytoplasmic membrane to it remains stable ( mono layer of Archea)
83
Q

Protection mechanisms to keep DNA stable at high temperatures

A

GC rich

84
Q

What is the name of DNA polymerase that is adapted to high temperatures

A

taq polymerase

85
Q

Who can resist high temperatures, but not metabolically active

A

Endospores

86
Q

What is the adaptation to low pH

A

Changes in cytoplasmic membrane to withstand high proton concentration. Bacteria lyse at higher pH, becasue the membrane becomes unstable

87
Q

Adaptation to high pH

A
  • Changes in cytoplasmic membrane
  • Use of Na gradient for transport and motility , because hard maintain pmf
  • Keep the electron transport chain close to ATPase, so protons are pumped out do not diffuse away
88
Q

How alkaphiles are used in industry

A

Proteases and lipases are added to laundry detergents

89
Q

Who are halophiles

A

Microorganisms that can grow at high salt concentration

90
Q

What is concentration of NaCl in seawater

A

3 %

91
Q

Obligate and facultative aerobes are usually grown

A

in liquid with constant shaking of the culture to ensure sufficient O2 concentration in the medium

92
Q

What does thioglycerate do

A

added to the medium to reduce O2 to H20 wgich creates a gradient of oxygen concentration ( top layer- oxic zone, lower-anoxic zone)

93
Q

What is reazurin

A

Redox indicater used to differentiate oxic and anoxic zones ( pink when oxidized)

94
Q

Who are microaerophiles

A

A microaerophile is a microorganism that requires oxygen to survive, but requires environments containing lower levels of oxygen than are present in the atmosphere

95
Q

Who are aerotolerant anaerobes

A

They do not utilize oxygen, but they can protect themselves from reactive oxygen molecules

96
Q

What is the harmful oxygen

A

Superoxide O2-
We can get it when H20 os oxidized to O2 during photosynthesis
Or flavoproteins , quinine and iron-sulfur proteins can virtually reduce O2 to O2-

Cells also want to get rid of H2O2 and hydroxyl radical

97
Q

How aerobes and facultative aerobes protect themselves from oxygen

A

They have catalase (it takes peroxide and with NADH converts it water) and superoxide dismutase (it takes superoxide and converts it to water and oxygen)

Introductory Microbiology (21 decks)

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