Bacterial Growth Flashcards

1
Q

What are the methods to determine bacterial growth?

A

determination of cell number

  • total cell count = by microbiologist using a microscope
  • coulter counter

viable cell count

  • identify number of actively growing or dividing cells in a sample = grow a known volume on a nutrient medium
  • must be diluted to stop overlapping of colonies and inaccurate count
  • plate count method (colony becomes visible) = spread plate, pour plate = count the number of colonies, calculate concentration by multiplying the count with the known volume

determination of cell mass

  • dry weight measurement = weigh after water has been removed
  • turbidity = more cells means higher turbidity resulting in a cloudier/opaque/less transparent solution = convert the detected turbidity into concentration using spectrophotometer

determination of cell constituents
- measure specific constituents = example - DNA

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2
Q

What is colony forming unit (CFU)?

A

CFU is used to estimate the concentration of microorganisms in a sample
- it is a measure of viable cells in which a colony represents an aggregate of cells derived from a single progenitor cell (original cell)

  • used to determine the number of viable bacterial cells in a sample per ml = concentration
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3
Q

How is the CFU calculated from an agar plate?

A

the number of visible colonies present on an agar plate can be multiplied by the dilution factor to get the CFU
- gives the number of viable bacteria cells in a sample per ml = concentration

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4
Q

What are the three types of bacteria and the optimal temperatures they grow at?

A

psychrophile = less than 20
- capable of growth and reproduction at low temperatures
mesophile = 16-40
- capable of growth at medium temperatures
thermophile = more than 40
- capable of growth at high temperatures

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5
Q

What happens to bacteria at low and high temperatures? What happens to bacteria at 37 degrees Celsius?

A

at low temperatures bacteria are dormant
at high temperatures bacteria are killed = denatured

at 37

  • most bacteria/pathogens multiply quickly
  • as temperature rises above and drops below, growth slows down
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6
Q

What are photoautotrophs and photoheterotrophs?

A

photoautotrophs

  • make their own food and energy by photosynthesis
  • use light (sunlight) as their energy source
  • use carbon dioxide as their primary carbon source
  • can fix carbon = convert inorganic carbon into organic carbon for use in cellular functions = biosynthesis, respiration

photoheterotrophs

  • depend on organic matter already produced by other organisms for nourishment (nutrients)
  • use light as their energy source
  • use organic compounds as their primary carbon source
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7
Q

What are chemoautotrophs and chemoheterotrophs?

A

chemoautotrophs

  • make their own food and energy = obtain energy for this from the oxidation of electron donors (inorganic compounds) in their environment
  • use inorganic compounds as their energy source = hydrogen, ammonia, hydrogen sulphide
  • use carbon dioxide as their primary carbon source

chemoheterotrophs

  • depend on organic matter already produced by other organisms for their nourishment (nutrients)
  • use organic compounds as their energy source
  • use organic compounds as their primary carbon source
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8
Q

What are inorganic compounds?

A

lack carbon and hydrogen

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9
Q

What are growth factors? What are the different categories of growth factors?

A

growth factors are required in small amounts to fulfil specific roles in biosynthesis
can be synthesised using their own carbon source = does not require an outside source
- purines and pyrimidines = required for the synthesis of DNA and RNA
- amino acids = required for protein synthesis
- vitamins = needed as coenzymes and functional groups of certain enzymes

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10
Q

Why are growth factors needed?

A

the need for growth factors is a result of blocked or missing metabolic pathways in the cells

they are not needed by all bacteria

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11
Q

What is the symbol for water activity?

What are

  • halophiles
  • osmophiles
  • xerophiles
A

water activity = Aw
pure water = Aw of 1.0
- decreases as water becomes more concentrated

halophiles - require NaCl for growth = thrive in high slat concentrations, low Aw

osmophiles - thrive in environments with high osmotic activity = high sugar concentrated environments

xerophiles - thrive in dry environments = low water activity/availability

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12
Q

What are the different types of anaerobes?

A

obligate anaerobes
- require oxygen for growth

obligate anaerobe

  • do not need or use oxygen as a nutrient source
  • harmed by presence of oxygen

facultative anaerobes/ facultative aerobes

  • organisms that can switch between aerobic and aerobic types of metabolism
  • can growth with or without oxygen

aerotolerant anaerobes

  • bacteria with exclusively anaerobic type of metabolism = fermentation
  • are insensitive to oxygen = can tolerate its presence
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13
Q

How do anaerobes and aerobes prevent the lethal accumulation of hydrogen peroxide and superoxide?

A

hydrogen peroxide and superoxide are produced by leaks of electrons from the mitochondrial electron transport chain

aerobe 
hydrogen peroxide is removed by 
- catalase = decomposes it 
superoxide is removed by 
- superoxide dismutase = prevents accumulation 

anaerobe

  • lack superoxide dismutase and catalase
  • undergo lethal oxidations by various oxygen radicals
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14
Q

What are the three types of bacteria and the optimum pH they grow at?
What are the range of pH that an organism grows over defined as?

A

acidophiles - less than pH 7
neutrophiles - neutral pH = 5-8
alkaliphiles - more than pH 7 = grow slowly at pH 6/7 and optimum is pH 9

range of pH is defined as

  • minimum
  • maximum
  • optimum
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15
Q

What is binary fission?

A

asexual reproductor by the separation of a body into 2 bodies = 2 identical daughter cells (identical to the parent cell)
- growth of cell = usually by lengthening

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16
Q

What is the process of binary fission?

A

1 - cell growth = elongates
2 - replication of chromosomes begins at the origin of replication = continues into both directions at once (bidirectional)
3 - FtsZ proteins migrate to the centre of the cell
4 - duplicated chromosome separate and move to the opposite ends of the cell. FtsZ proteins form a ring around the periphery of the midpoint of the chromosomes
5 - FtsZ directs the formation of the septum that divides the cell. Plasma membrane and cell wall material accumulate.
6 - once the septum is formed, the cell pinches into two and separates
7 - two identical daughter cells have been formed. FtsZ is dispersed throughout the cytoplasm of the cells

FtsZ - cell division protein

17
Q

What is sporulation?

A

survival mechanism
formation of endospores by vegetative cells
- initiated when conditions for growth of vegetative cells become unfavourable

18
Q

What is germination? What are the three steps?

A

germination
- endospores can remain dormant for years but when conditions allow they can convert back to vegetative cells rapidly

germination has three steps
1 - activation
2 - germination
3 - outgrowth

19
Q

What are endospores?

A

formed from vegetative cells

  • formed within the intracellular compartment of the mother cell
  • mother cell does not survive, only the spore does

preserves the genetic material of the bacterial cell

20
Q

What are the steps for sporulation?

A

1 - DNA replicates and extends into the axial filament = across the whole cell

2 - asymmetric separation

  • forespore gets one copy of the DNA and the mother cell gets one copy = move to opposite poles
  • septum forms asymetrically, closer to the forespore

3 - engulfment and protoplast formation
- mother cell engulfs the forespore and forms a second membrane around it = double membrane

4 - cortex formation
- peptidoglycan cortex forms between the membrane of the original forespore and the mother cell

5 - dipicolinate acid is synthesised and calcium is incorporated into the spore coat
- addition of calcium removes water = dehydration, as a result heat resistance increases

6 - coat formation

  • proteins forms around the cortex = spore coat
  • spore becomes mature

7 - lysis
- mother cell undergoes lysis/ disintegration of the chromosomes and releases the spore

21
Q

What are the stages of bacterial growth?

A

1 - lag phase

  • no increase in cell number = bacteria are preparing for reproduction and DNA synthesis
  • increase in cell size only

2 - log phase = exponential phase

  • increase in cell/bacterial number
  • bacterial biomass increases linearly with time

3 - stationary phase

  • number of bacteria reaches maximum
  • no further increase in cell number = metabolic rate is decreased as metabolic products accumulate

growth rate = death rate

4 - death phase

  • number of viable bacteria begin to decline
  • no further divisions