Chapter 5: Microbial Growth and its Control

Question 1

Growth

Answer 1

-increases in the number of cells

Question 2

Binary fission

Answer 2

-cell division following enlargement of cell to twice its minimum size

Question 3

One generation

Answer 3

• cell elongation
• septum formation
• completion of septum; formation of walls; cells separate

Question 4

Septum

Answer 4

-partition between dividing cells, pinches off between two daughter cells

Question 5

Generation time

Answer 5

• time required for microbial cells to double in number

- depends on nutritional and generic factors and temperature

Question 6

During cell division

Answer 6

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

Question 7

Budding

Answer 7

• results from unequal cell growth and forms totally new daughter cell
• form cytoplasmic extensions such as stacks (caulobacter), hyphae, (hyphomicrobium), and appendages (ancalomicrobium)

Question 8

Cytoplasmic structure

Answer 8

-are not partitioned and remain in old cell

Question 9

Cell division in bacteria

Answer 9

• equal products of cell division
  
  • binary fission: most bacteria
• unequal products of cell division
  
  • simple budding: pirellula, blastobacter
  • budding from hyphae: hyphomicrobium, rhodomicrobium, pedomicrobium
  • cell division of staked organism: caulobacter
  • polar growth without differentiation of cell size: rhodopseudomonas, nitrobacteria, methylosinus

Question 10

Planktonic growth

Answer 10

-growth as suspension

Question 11

Sessile growth

Answer 11

• attached to surface
• can develop into biofilms
• attached polysaccharide matrix containing embedded bacteria

Question 12

Biofilms form in stages

Answer 12

• planktonic cells attach

- sticky matrix forms

Question 13

Microbial mats

Answer 13

-multilayered sheets with different in each layer

Question 14

BiofIlms

Answer 14

• prevent harmful chemicals from penetrating
• prevent protists from grazing
• prevent washing away of cells
• affect human health
• water distribution systems
• fuel storage

Question 15

Exponential growth

Answer 15

-growth of a microbial population in which cell numbers double within a specific time interval

Question 16

N=N_02^n (2^0→2^1→2^2)

Answer 16

• a relationship exists between the initial number of cells present in a culture and the number present after a period of exponential growth
• N is the final cell number
• N_0 is the initial cell number
• n is the number of generations during the period of exponential growth

Question 17

g=t/n

Answer 17

• generation time (g) of the exponentially growing population
• t is the duration of exponential growth (days/hours/minutes)
• n is the number of generations during the period of exponential growth
• can be calculated from slope of the straight-line logarithmic growth plot

Question 18

Instantaneous growth rate constant

Answer 18

-(k) expresses rate of growth at any instant (measure in h^-1)

Question 19

Instantaneous growth rate

Answer 19

• (k) is calculated as k=0.693/g

- useful for optimizing culture conditions for microorganism growth

Question 20

Batch culture

Answer 20

-a closed-system microbial culture of fixed volume

Question 21

Typical growth curve for population of cells grown in a closed system is characterized by four phases

Answer 21

• lag phase
• exponential phase
• stationary phase
• death phase

Question 22

Lag phase

Answer 22

• interval between inoculation of a culture and beginning growth
• time needed for biosynthesis of new enzymes and to produce required metabolites before growth can begin

Question 23

Exponential phase

Answer 23

-cells in this phase are typically in the healthiest state

Question 24

Stationary phase

Answer 24

• growth rate of population is zero
• either an essential nutrient is used up or waste products accumulate
• some cells grow while others die, balancing each other

Question 25

Death phase

Answer 25

- is inoculation continues after cells reach stationary phase, the cells will eventually die - typically much slower than exponential growth - re-adjust to dormant stage - viable cells remain for months or years

Question 26

Continuous culture

Answer 26

-an apen system, microbial culture of fixed volume

Question 27

Chemostat

Answer 27

-most common type of continuous culture device

Question 28

Dilution rate

Answer 28

- F/V - F is the flow of adding fresh medium and removing spent medium - V is the culture volume - concentration of a limiting nutrient - both growth rate and population density of culture can be controlled independently and simultaneously

Question 29

Steady state

Answer 29

- cell density and substrate concentration do not change over time - specific growth rate (D)= decrease in cell numbers due to dilution - experimental uses: - can maintain exponential growth phase for weeks/months - used for study physiology, microbial ecology and evolution, enriched and isolate of bacteria from nature - growth rate controlled by dilution rate

Question 30

Culture media

Answer 30

- nutrient used to grow microbes in the laboratory | - typically sterilized in an autoclave

Question 31

Defined media

Answer 31

-exact chemical composition known

Question 32

Complex media

Answer 32

-composed of digests of microbial, animal, or plant products

Question 33

Enriched media

Answer 33

- contain complex media plus highly nutritious materials | - used to culture fastidious (nutritionally demanding) microbes

Question 34

Selective media

Answer 34

-contain compounds that selectively inhibit growth of some microbes but not other

Question 35

Differential media

Answer 35

-contain an indicator, usually a dye, that detects particular metabolic but not during growth

Question 36

Microbes

Answer 36

- sterilization of media is critical | - to prevent contamination, aseptic techniques should be followed

Question 37

Total cell count

Answer 37

-counting chambers with squares etched in a slide for liquid samples

Question 38

Microscopic cell count

Answer 38

-observing and enumerating cells present dried on slides or on liquid samples

Question 39

Limitations of microscopic cell counts

Answer 39

- cannot distinguish between live vs dead cells without special stains - precision is difficult to achieve - phase-contrast microscope required if a stain is not used - cell suspensions of low density hard to count - motile cells need to immobilized - debris in sample can be mistaken for cells

Question 40

Microscopic cell counts in microbial ecology

Answer 40

-often used to natural samples -use stains to visualize and provide phylogenetic information or metabolic properties -DAPI (blue) reacts with DNA -other fluorescent stains differentiate live and dead cells phylogenetic stains can determine properties of bacteria and archaea