Chapter 5: Microbial Growth Flashcards Preview

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Flashcards in Chapter 5: Microbial Growth Deck (70):
1

Growth

Measured as an increase in the number of cells

2

Binary fission

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

3

Generation time

Time required for microbial cells to double in number

4

Each daughter cell receives during cell division

A chromosome and sufficient copies of all other cell constituents to exist as an independent cell

5

What occurs simultaneously in bacteria and archaea?

Growth in cell size, chromosome replication, and septum formation

6

Is there mitosis in bacteria and archaea?

No

7

Generation time is dependent on

Growth medium and incubation conditions: carbon source, pH, temperature, etc.

8

Exponential growth

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

9

What kind of curve does exponential growth create?

One that has a slope that increases continuously

10

Growth rate (k)

Rate of increase in population number or biomass.
Expressed in bacteria and archaea as number of doublings per hour

11

Generation time

Time it takes for each to cell to become 2 cells

12

Specific growth rate

Fastest growth rate in the best medium and optimal temperatures

13

Batch culture

Closed-system microbial culture of fixed volume

14

Lag phase

Interval between inoculation of a culture and beginning of growth

15

Exponential phase

Cells in this phase are typically in the healthiest state

16

Stationary phase

Cells metabolically active, but growth rate of population is zero

17

Why is growth rate in stationary phase zero?

Either an essential nutrient is use up, or waste product of the organism accumulates in the medium

18

Death phase

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

19

Do all bacteria die in the death phase?

Some bacteria form spores/cysts or dormant stage that allow a significant proportion of cells to survive for a long time

20

Continuous culture

Open-system microbial culture of fixed volume

21

Chemostat

Most common type of continuous culture device
Both growth rate and population density of culture can be controlled independently and simultaneously

22

Dilution rate

Rate at which fresh medium is pumped in and spent medium is pumped out

23

Concentration of limiting nutrient controls

Population size and the growth rate

24

How are microbial cells counted by direct microscopic observations?

Petroff-Hausser counting chamber

25

Petroff-Hausser counting chamber

Each square corresponds to a calibrated volume

26

Limitations of microscopic counts

- Cannot distinguish between live and dead cells without special stains
- Small cells can be overlooked
- Precision is difficult to achieve
- Phase-contrast microscope required if a stain is not used
- Low density cell suspensions are hard to count
- Motile cells need to be immobilized
- Debris in sample can be mistaken for cells
- Brownian motion, some forms clumps

27

Flow cytometer

Second method for counting cells in liquid samples
Uses laser beams, fluorescent dyes, and electronics

28

Viable cell counts (plate counts)

Measurement of only living cells capable of growing to form a population

29

Methods of plate counts

Spread-plate method
Pour-plate method

30

Viable count issues

- Preparation and incubation time
- Unreliable on counts of natural samples
- Culture media and growth conditions can't grow every microbe

31

The great plate anomaly

Direct microscope counts of natural sample reveal far more organisms than those recoverable on plates

32

How much microbial diversity is culturable?

1-10%

33

What supports the great plate anomaly?

Microscope methods count dead cells, whereas viable methods do not
Different organisms may have vastly different requirements for growth

34

Turbidity measurements

Indirect, rapid, and useful methods of measuring microbial growth

35

How is turbidity measured?

With a spectrophotometer

36

What is turbidity measured in?

Optical density

37

Why is turbidity measured in optical density?

Bacteria behave like small particles and absorb and scatter light

38

The larger the number of particles...

The greater the absorbance and the lower the light transmission to the photocell

39

Does absorbance distinguish cells?

No it can't tell live cells from dead cell or if it's chemical particles

40

Does turbidity require a stain?

No they do not disturb the sample

41

How is direct cell related to turbidity?

A standard curve must first be established to another counting method

42

What other counting methods are there?

Viable cell count
Weight of biomass produced
Measuring other parts of the cell which are proportional the the whole mass of cells

43

Issues with optical density

- Has a finite linear range of measurement
- Only works if the cells are evenly distributed throughout the medium
- Cuvette must not have scratches
- Culture may need to be diluted when the cells are at a very high density

44

Cardinal temperature

Minimum, optimum, and maximum temperatures at which an organism grows

45

Psychrophile

Low temperature

46

Mesophile

Midrange temperature

47

Thermophile

High temperature

48

Hyperthermophile

Very high temperature

49

Where are mesophiles found?

In warm-blooded animals, terrestrial and aquatic environments, temperate and tropical latitudes

50

Extremophiles

Organisms that grow under very hot or very cold conditions

51

Psychrophile temperature optima

Less than 20 degrees celsius

52

Psychophile environments

Permanently cold environments: deep oceans, Arctic and Antarctic environments

53

Psychotolerant

Organisms that can grow at 0 degrees celsius but have optima of 20-40 degrees celsius

54

Molecular adaptations that support psychrophily

Production of enzymes that function optimally in the cold
Modified cytoplasmic membranes - high unsaturated fatty acid content

55

What life forms exist at above 65 degrees celsius?

Prokaryotes - chemorganotrophic and chemolithotrophic

56

What is the upper limit temperature of phototrophy?

70 degrees celsius

57

Thermophile optimal temperature

45-80 degrees celsius

58

Hyperthermophile optimal temperature

Greater than 80 degrees celsius

59

Hyperthermophile environments

Boiling hot springs and seafloor hydrothermal vents

60

Methanopyrus kandleri

Archaeon that can grow at 122 degrees celsius

61

Molecular adaptations to thermophily

Specific modifications provide thermal stability to enzymes and proteins
Modifications in cytoplasmic membranes to ensure stability

62

Bacteria have what to survive high temperatures

Lipids rich in saturated fatty acids

63

Archaea have what to survive high temperatures

Lipid monolayer rather than bilayer

64

What produces enzymes widely used in industrial microbiology?

Hyperthermophiles

65

Taq polymerase

Used to automate the repetitive steps in the polymerase chain reaction technique

66

Hydrolytic enzymes

Proteases, cellulases, lipases

67

True/false: enzymes of thermophiles are more stable and tend to have higher activity than mesophilic counterparts

True

68

What are the upper temperature limits for life?

Suggested at 140-150 degrees celsius

69

What are the closest descendants of ancient microbes?

Hyperthermophiles

70

What supports the theory that hyperthermophiles are the closest descendants?

- Are found on the deepest, shortest branches of phylogenetic tree
- Oxidation of H2 is common to many hyperthermophiles and may have been the first energy-yielding metabolism