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MBIO 1010 > Lecture 4: Microbial Growth > Flashcards

Lecture 4: Microbial Growth Flashcards

1
Q

_____: measured as an increase in the
number of cells

A

Growth

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2
Q

______: cell division following enlargement of a cell to twice its minimum size

A

Binary fission

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3
Q

_______: time required for microbial cells to double in number

A

Generation time

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4
Q

In _____ & ______, growth in cell size, chromosome replication and even
septum formation typically occur simultaneously

contrary to Eukaryotic cells where there is an interphase AND mitosis

A

bacteria and Archaea

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5
Q

T/F: Mitosis does not occur in bacteria and Archaea

A

true!

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6
Q

T/F: Most bacteria have shorter generation times than eukaryotic microbes

A

true!

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7
Q

what does generation time depend on?

A

growth medium and incubation conditions! carbon source, pH, temp. etc.

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8
Q

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

A

exponential growth

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9
Q

A relationship exists between the initial number of cells present in a
culture and the number present after a period of exponential growth: what is this equation?

A

Nt = No x 2^n

Nt: final cell #
No: initial cell #
n: # generations during period of exponential growth

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10
Q

on what scale do we always plot exponential growth?

A

log scale

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11
Q

T/F: When growth is unlimited it is called exponential growth because
it generates a curve whose slope increases continuously

A

true!

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12
Q

growth rate (k)= ?

A

rate of increase in population # or biomass

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13
Q

Since bacteria and archaea grow by binary fission, the growth rate is
expressed as the number of _______ per hour

A

doublings

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14
Q

generation time (g): ?

A

time it takes for each cell to become 2 cells

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15
Q

specific growth rate formula?

A

k= (Log Nt - Log N0)/ 0.301 (delta t)

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16
Q

generation time (g) formula?

A

g= 1/k

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17
Q

For each organism there is a specific growth rate that is the fastest growth rate in the best growth medium at optimal temperature, are all of them the same?

A

no! different for each individual organism

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18
Q

______: a closed-system microbial culture of fixed volume

A

Batch culture

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19
Q

what are the four phases of a typical growth curve of a closed system?

A

Lag phase, Exponential phase, Stationary phase, Death phase

20
Q

_____: Interval between inoculation of a culture and beginning of growth

A

Lag phase

21
Q

____: Cells in this phase are typically in the healthiest state

A

Exponential phase

22
Q

_______: 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

A

Stationary Phase

23
Q

_______: If incubation continues after cells reach stationary phase, the cells will
eventually die

Not all bacteria die, some bacteria (gram +!!)
form spores/cysts or dormant stages
that allow a significant proportion of
cells to survive for a long time

A

Death phase

24
Q

________: an open-system microbial culture of fixed volume

A

Continuous culture

25
Q

T/F: there is no stationary phase in a continuous culture

A

true! conditions stay ideal to the bacteria

26
Q

what is the most common type of continuous culture device?

A

chemostat

27
Q

in a _____, Both growth rate and population density of
culture can be controlled independently and
simultaneously

A

chemostat

28
Q

______: rate at which fresh medium is
pumped in and spent medium is pumped out

A

Dilution rate

29
Q

T/F: Concentration of a limiting nutrient controls the
population size and the growth rate

A

true!

30
Q

______: Microbial cells can be enumerated by direct microscopic observations using a Petroff-Hausser counting chamber

A

microbial counts, each square corresponds to a calibrated volume

31
Q

why are microscopic bacterial counts unreliable?

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 (<106 cells/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

32
Q

________ is an
alternative method that can
be used to count the total
number of cells

A

Flow Cytometry

33
Q

what does flow cytometry use to count cells?

A

laser beams, fluorescent dyes, electronics

34
Q

________: measure only living cells

A

viable cell counts, only counts cells capable of growing to form a population

35
Q

what are the two main ways to perform a viable cell plate count?

A

spread-plate
pour-plate

36
Q

bacteria show _____ growth when using the spread-plate method

A

surface

37
Q

bacteria show _____ growth when using the pour-plate method

A

3D

38
Q

what are the three main issues with viable cell count methods?

A

requires lots of prep
plate counts can be highly unreliable
selective culture media and growth conditions only target particular species

39
Q

the great plate anomaly
T/F: Modern genomic techniques suggest that only 1-10% of microbial diversity is
culturable from most environmental samples (including the diversity of
organisms in our own microbiomes)

A

true! direct microscopic counts of samples reveal far more organisms than those recoverable on plates

40
Q

why do microscopic counts reveal so many more organisms?

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

41
Q

how do we use spectrophotometry to count bacteria?

A

turbidity is measured with a
spectrophotometer, and measurement is
referred to as optical density (OD)

the more cells, the more absorption, the lower the light reading on the spec

42
Q

what is the one caution of using a spec to count cells?

A

absorbance does not distinguish
dead cells from living cells!

43
Q

_______: Typically do not require destruction or
significant disturbance of sample (some spectrophotometers are specifically designed to use growth tubes as cuvette)

A

Turbidity measurements, can use the sample again!

44
Q

To relate a direct cell count to a turbidity value, a _____ must
first be established to another counting
method

A

standard curve

45
Q

what are the four problems with using optical density for cell counts?

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

46
Q

what are the two other counting techniques not already described?

A

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

There are other spectrometric techniques to measure specific components of the cell: protein, DNA etc. which are proportional to
the whole mass of cells
(have to account for error)

MBIO 1010 (12 decks)

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