Microbial growth Flashcards
1
Q
6 essential elements for e.coli growth
A
Carbon Oxygen Nitrogen Hydrogen Phosphorus Selenium
2
Q
Micronutrients for e.coli growth
A
Iron
Trace metals
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
4
Q
From what sources can carbon be obtained for e.coli
A
CO2, organic compounds
5
Q
From what sources can nitrogen be obtained for e.coli
A
NH3
NO3-
N2
organic nitrogen compounds (amino acids)
6
Q
From what sources can hydrogen be obtained for e.coli
A
H2O
Organic compounds
7
Q
From what sources can oxygen be obtained for e.coli
A
H2O
O2
organic compounds
8
Q
From what sources can phosphorus be obtained for e.coli
A
PO4
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)
10
Q
From what sources can potassium be obtained for e.coli
A
K+ in solution or various K salts
11
Q
From what sources can magnesium be obtained for e.coli
A
Mg in solution or various Mg salts
12
Q
From what sources can calcium be obtained for e.coli
A
Ca in solution or various Ca salts
13
Q
From what sources can sodium be obtained for e.coli
A
Na in solution or various Na salts
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
15
Q
What is the growth of population
A
Increase number of cells or biomass
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
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
18
Q
What is the usual time for e.coli to divide
A
20 minutes
19
Q
What does cell division require ( cell wall)
A
Synthesize of new cell wall material, but also requires its destruction by autolysins
20
Q
What does bactoprenol do
A
It brings new peptidoglycan subunits across the cytoplasmic membrane
21
Q
What enzymes incorporates new peptidoglycan subunits ?
A
Transpeptidases
Transglycosylases
22
Q
What is formed at theseptum when cell is dividing
A
FtsZ ring
23
Q
What does FtsZ ring do
A
It contracts and allows the cells to pinch off from each other in two different cells
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
25
What is a wall band
Scar between old and new peptidoglycan
26
What mechanism of cell division in Archea
Similar to bacteria
27
What is MacConkey medium
Selective medium
| It has bile salts that inhibit growth of Gram+ bacteria, permissive for Gram negative enteric pathogen (e.coli)
28
Why MacConkey Agar is a differential media
It allows to distinguish between Lactose ferments (Pink) and Lactose non-ferments (colorless)
29
What reaction happens on MacConkey Agar and lactose
Lactose is a galactose +glucose
Glucose->glycolytic pathway->fermentation of lactate ( reduce pH)
The change of pH changes the color
30
What color do e.coli turn on MacConkey Agar
Dark pink because it is able of lactose fermentation
31
What kind of medium is Mannitol-salt and explain its action
Selective medium
High in NaCl: inhibits most Gram- and Gram+
Used for isolation or detection of Staphylococcus
32
Mannitol fermenters will show what result in Manitol-salt media
Yellow- manitol dermenters
Pink-manitol negative
Staphylococcus aureus is manitol +
Staphylococcus epidermidis-pink
33
Two different methods of creating agar sample with bacteria
Spread-plate method ( only on top)
| Pour-plate method ( throughout the agar)
34
What is the number range for a reliable result?
Between 30-300 colonies
35
At what temperature do e.coli grow
37
36
What is the purpose of serial dilution
To get a viable count of such cultures, serial dilutions have to be made
37
The formula for CFU
Number of colonies \(dilution plated* volume plated)
38
What is the advantage of microscopic counts vs serial dilution
In microscopic counts you can count dead bacteria as well as alive + no need to wait until bacteria grow
39
What is used for microscopic counts?
Counting chamber
40
What is the disadvantage of microscopic counts
Small cells can be missed (magnification is not enough) , motile cells are hard to count and must be immobolized
41
What is the work principle of flow cytometry
Every time a cell passes the laser it counts it, because the laser is interrupted
42
Flow cytometry is better in counting what kind of cells
Big cells: protozoan,yeast,mammalian cells,etc.
43
What is the advantage of flow cymmetry
Can be used to sort cells according to size, shape,labeling,etc.
Different types of cells or species can be labelled
44
We use the dead to control to know what
Where the cells are dead.To define after at the test sample where the dead cells are. To establish this area
45
The disadvantage of flow cytometry
Time consuming and expensive
46
What is the usual method that is used to quantify bacteria in the lab
Turbidimetric method
47
Explain the principle of Turbidimetric method
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
What concentration should be used for Turbidimetric method
not too dense , so the the readings can be reliable (0.1 to 1 OD)
49
Turbidimetric method measures both ___ and ___
Living and dead cells
50
OD is affected by ___
Properties of cells: size, clumping,etc.
51
What is the extra step that you need to do after Turbidimetric method
You need to make a relationship between OD and cell number( microscopy counts) and then the graph should be made
52
What is generation time
Time needed for the population to double
53
Generation time depends on ___
Growth medium and the conditions
54
When the conditions are right, microorganisms can grow ___
Exponentially ( doubling at a constant rate)
55
What is the formula for number of cells in some time
N(number of cells)=N0(number of cells initially)*2^n , where n is number of generation
56
What is generation time
The time it takes for bacteria to double
57
What is the formula for generation time
g=t/n
58
When you make a graph cells/time , the steeper the line , then ___
The smaller the time when population doubles
59
Why for bacteria growth in the lab Erlenmeyer flask is used
we like to put on the shaking table , do not splash and has a big air space , so the culture is kept aerated
60
What are the usual growth phases of bacteria
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
Dead bacteria do not contribute to ___
OD
62
Two phases with exponential function
Exponential growth and death phase
63
What medium mimics natural conditions the most
continuous culture
64
What is the chemostat
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
What are we changing with the chemostat
Dilution rate: at what rate there is an addition of fresh medium.
66
What is important about the dilution rate
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
Once equilibrium is reached, ____
Number of cells is constant; the growth rate equals the death rate ( washout)
68
Most microbial species grow as
A mixed culture with other organisms
69
Who are extremophiles
Microorganisms that grow preferentially under extreme conditions
70
What happens at minimum, optimal and maxiumum temperatures
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
Who are psychrotolerant
Organisms that can grow at 0 C but have optima around 20-40 C
72
Who are psychrophiles
Optimum temperature 4 C, but they can grow less than 0
73
Who are mesophiles
Grow around body temperatureto 39 C
74
Who are thermophiles
Grow around 60 C
75
Who are hyperthermophile
88 C or even 106 C
76
What microorganisms grow at -15 C
Planococcus halocryophilus
77
What really kills microorganisms in cold
Not the temperature, but ice crystals
78
What are adaptations to cold temperatures
- 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
What are cryoprotectants
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
Microbial cultures are preserves at
-80 or -196 C in liquid nitrogen
81
Who are barophillic bacteria
Grow best at high pressure
82
Adaptations to high temperatures
- 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
Protection mechanisms to keep DNA stable at high temperatures
GC rich
84
What is the name of DNA polymerase that is adapted to high temperatures
taq polymerase
85
Who can resist high temperatures, but not metabolically active
Endospores
86
What is the adaptation to low pH
Changes in cytoplasmic membrane to withstand high proton concentration. Bacteria lyse at higher pH, becasue the membrane becomes unstable
87
Adaptation to high pH
- 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
How alkaphiles are used in industry
Proteases and lipases are added to laundry detergents
89
Who are halophiles
Microorganisms that can grow at high salt concentration
90
What is concentration of NaCl in seawater
3 %
91
Obligate and facultative aerobes are usually grown
in liquid with constant shaking of the culture to ensure sufficient O2 concentration in the medium
92
What does thioglycerate do
added to the medium to reduce O2 to H20 wgich creates a gradient of oxygen concentration ( top layer- oxic zone, lower-anoxic zone)
93
What is reazurin
Redox indicater used to differentiate oxic and anoxic zones ( pink when oxidized)
94
Who are microaerophiles
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
Who are aerotolerant anaerobes
They do not utilize oxygen, but they can protect themselves from reactive oxygen molecules
96
What is the harmful oxygen
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
How aerobes and facultative aerobes protect themselves from oxygen
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)
