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MBIO 1010 > Microbial Growth > Flashcards

Microbial Growth Flashcards

Lectures 18-20

1
Q

What is Binary Fission?

A

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

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2
Q

What is the term that describes the time required for microbial cells to double in number?

A

Generation time.

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3
Q

What occurs during cell division in binary fission?

A

Each daughter cell receives a chromosome and sufficient copies of all other cell constituents to exist as an independent cell.

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4
Q

True or False: In bacteria and Archaea, growth in cell size, chromosome replication and even septum formation typically occur at different stages.

A

False: All of those events occur simultaneously.

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5
Q

True or False: Mitosis does not occur in bacteria and archaea.

A

True

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6
Q

What is generation time dependent on? How does bacteria GT length compare to eukarya microbe GT length?

A

Generation time is dependent on growth medium and incubation conditions: carbon source, pH, temperature, etc. Most bacteria have shorter generation times than eukaryotic microbes.

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7
Q

What is the definition of exponential growth?

A

Growth of a microbial population in which cell numbers double at a constant and specific time interval.

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8
Q

What is the relationship that exponential growth explains?

A

A relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth.

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9
Q

What is the formula that describes exponential growth? What do the variables mean?

A

Formula: Nt = No x 2^n
Nt= final cell number
No= initial cell number
2^n= number of generations during the period of exponential growth

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10
Q

True or false: During exponential growth the growth rate starts off slow, but increases quite fast at the exponential curve.

A

True

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11
Q

Why is growth rate expressed as the amount of times a cell doubles per hour?

A

Because bacteria and archaea grow by binary fission.

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12
Q

What is the definition of growth rate (k)?

A

The rate of increase in population number or biomass.

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13
Q

What is the formula that describes growth rate? What do the variables mean?

A

k = (Log Nt –Log No)/[(0.301)(delta t)]
No=# of cells at time 1
Nt=# of cells at time 2
delta t= time1- time2

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14
Q

What is the formula for determining generation time from growth rate (k)?

A

g= 1/k

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15
Q

What term describes the fastest growth rate in the best growth medium at optimal temperature for an organism?

A

Specific growth rate

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16
Q

Which organism can grow less in than 30 min in a rich medium?

A

E. coli

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17
Q

Which organism cannot grow faster than one doubling every 24 hours?

A

Mycobacterium tuberculosis

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18
Q

Which organism can double in numbers every 10 minutes under optimal growth conditions (e.g. nice warm stew on a warming plate)?

A

Clostridium perfringens

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19
Q

What is a Batch Culture?

A

A closed-system microbial culture of fixed volume.

20
Q

What are the phase(s) a typical growth curve for population of cells grown in a closed system will go through?

A

Lag (or log) phase
Exponential phase
Stationary Phase
Death Phase

21
Q

What occurs in the stationary phase?

A

Cells metabolically active, but growth rate of population is zero.
Either an essential nutrient is used up, or waste product of the organism accumulates in the medium.

22
Q

In which phase are the cells typically the healthiest?

A

The exponential phase

23
Q

Which stage is the interval between inoculation of a culture and beginning of growth?

A

The lag phase

24
Q

If incubation continues after cells reach stationary phase, the cells will eventually die. Which phase does this occur in?

A

The death phase.

25
Q

True or False: Not all bacteria die, some bacteria for spores/cysts or dormant stages that allow a significant proportion of cells to survive for a long time.

A

True

26
Q

What is a continuous culture?

A

An open-system microbial culture of fixed volume.

27
Q

Which is one of the most common continuous culture devices that show both growth rate and population density of culture and can be controlled independently and simultaneously?

A

Chemostat

28
Q

What describes the rate at which fresh medium is pumped in and spent medium is pumped out?

A

Dilution rate

29
Q

What controls the population size and the growth rate in a chemostat?

A

The concentration of a limiting nutrient.

30
Q

What is one method to obtain a microbial count with a microscope?

A

Using the Petroff-Hausser counting chamber- a direct microscope observation using a square corresponded to a certain volume.

31
Q

What is the problem with the Petroff-Hausser counting chamber?

A

The counts can be unreliable due to not knowing which cells are alive or dead.

32
Q

What are the 8 limitations to microscopic counts?

A
  • Cannot distinguish between live and dead cells without special stains
  • Small cells can be overlooked
  • Precision is difficult to achieve (need a lot of counts)
  • Phase-contrast microscope required if a stain is not used
  • Cell suspensions of low density (<106cells/ml) hard to count
  • Motile cells need to immobilized
  • Debris in sample can be mistaken for cells
  • Cells may move (Brownian motion), some form clumps Based on random distribution and dispersal of the cells
33
Q

What is Flow Cytometry? What does it use to obtain microbial counts?

A

Flow Cytometry is an alternative method that can be used to count the total number of cells. It uses laser beams, fluorescent dyes, and electronics.

34
Q

What are viable cell counts?

A

Cell counts that measure only living cells which are capable of growing to form a population.

35
Q

What are the method(s) to obtain a plate count?

A

Spread-Plate method and Pour-Plate method.

36
Q

What are the 3 limitations to viable cell counts?

A

Requires lots of preparation (dilution tubes, agar plates), and incubation time (overnight or more) to get the measurements for a single culture
Plate counts can be highly unreliable when used to assess total cell numbers of natural samples (Ex: soil and water)
Selective culture media and growth conditions target only particular species
-A single medium will never grow every microbe
-Can only count the types of bacteria that can grow in the medium you selected to use

37
Q

What is the ‘great plate anomaly’?

A

Direct microscopic counts of natural samples reveal far more organisms than those recoverable on plates. This suggests 1-10% of microbial diversity is culturable from environmental samples, including our own microbiomes.

38
Q

Why does the ‘great plate anomaly’ occur?

A

Microscopic methods count dead cells, whereas viable methods do not. Different organisms may have vastly different requirements for growth. We do not know the specific requirements for all organisms.

39
Q

How do we achieve Spectrophotometric Counts?

A

We use turbidity measurements are indirect, rapid, and useful counting methods.

40
Q

Most often turbidity is measured with a spectrophotometer- what do we refer to the measurement as?

A

Optical Density (OD)

41
Q

How does a spectrophotometer work?

A

Since bacteria do behave like small particles and absorb and scatter light only a portion of the incident light makes it to the photocell because particles (including cells) scatter light. The larger the number of particles, the greater the absorbance, the lower the light transmission to the photocell.

42
Q

How do you relate a direct cell count to a turbidity value?

A

A standard curve must first be established to another counting method- either viable cell counts or the weight of biomass produced.

43
Q

What are the limitations to optical density?

A

Has a finite linear range of measurement
Only works if the cells are evenly distributed throughout the medium (no clumps or biofilms)
Cuvette must not have scratches
Culture may need to be diluted when the cells are at very high density
Doesn’t distinguish between dead and alive cells

44
Q

What are other cell counting techniques?

A

Total mass of cells (dry cell weight): a specific aliquot (volume) cells are concentrated, washed to remove media components, concentrated and dried

45
Q

What are other spectrophotometer techniques that can be used?

A

Techniques to measure specific components of the cell: protein, DNA etc. which are proportional to the whole mass of cells.

MBIO 1010 (14 decks)

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