Chapter_7_Bacterial and Archaeal Growth

Question 1

Describe the three phases of a bacterial cell cycle. The overlapping of cytokinesis and chromosome partitioning could potentially create problems for a cell during the cell cycle. What mechanisms does the cell use to prevent problems?

Answer 1

• 3 phases of the cell cycle are: growth phase, chromosome replication, cytokinesis
  The cell uses the divisome mechanism at the right time to avoid premature cytokinesis

Question 2

What elements of the Sulfolobus spp. cell cycle are similar to the bacterial cell cycle? What elements are similar to the eukaryotic cell cycle?

Answer 2

• Proteins segA and segB, and cytokinesis are similar to the bacterial cell cycle
  Cell cycle phases G1, S, G2, dna replication machinery, segA, segB, and histone like proteins are similar to the eukaryotic cell cycle

Question 3

Define microbial growth.

Answer 3

• The increase in # of cells in a microbial population
• Measured in terms of population size over time
  Uses a growth curve

Question 4

Describe the phases of the growth curve and discuss the causes of each.

Answer 4

• Lag phase: cells adapt to new conditions and synthesize necessary components
• Log phase: cells divide exponentially
• Stationary phase: growth slows due to nutrient depletion or waste accumulation
• Death phase: cells die at a constant rate
  Long term stationary phase: population levels remains constant

Question 5

Why must k and g be calculated from exponential phase measurements?

Answer 5

• K is growth rate constant
• G is generation time
• Growth is constant during exponential phase
  There is an accurate doubling time during exponential phase

Question 6

Why would vigorously growing cells have a shorter lag phase than those that have been stored in a refrigerator when inoculated into fresh culture medium?

Answer 6

• Vigorously growing cells are already adapted to the environmental conditions
  Cells in a refrigerator need to adapt to environment in order to start growing

Question 7

How do microorganisms adapt to hypotonic and hypertonic environments?

Answer 7

• To adapt to hypotonic environments they need to release solutes from inside the cell through mechanosensitive channels
  In hypertonic environments they have to increase solute concentration inside the cell

Question 8

What are halophiles and why do they require sodium and potassium ions?

Answer 8

• Halophiles are microorganisms that thrive in high salt concentrations
• They need Na+ and K+ to balance osmotic pressure between their cytoplasm and high salt external environment
  Salt in: high K+ in cytoplasm, high Na+ in external environment

Question 9

Define water activity. Why is it difficult for microorganisms to grow at low aw values?

Answer 9

• Water activity is the availability of water for microbial growth
  Difficult for microbes to survive w/o water due to osmotic stress, loss of proteins etc…

Question 10

Why does the growth rate rise with increasing temperature and then fall again at higher temperatures?

Answer 10

• Increased enzyme activity, membrane fluidity, metabolic rates with rising temp
  Enzyme denaturation, instability, dna damage with too high temp

Question 11

Identify environments where you could find microbes considered psychrophilic, psychrotolerant, mesophilic, thermophilic, and hyperthermophilic

Answer 11

• Psychrophiles = 0-20C
• Psychrotrophs = 0-35C
• Mesophiles = 20-45C
• Thermophiles = 45-80C
  Hyperthermophiles = 85-113C

Question 12

Describe the five types of O2 relationships seen in microorganisms.

Answer 12

• Obligate aerobe = needs o2
• Microaerophile = needs 2-10% o2
• Facultative anaerobe = doesn’t need o2 but grows better with it
• Aerotolerant anaerobes = grow w or w/o o2
  Strict anaerobe = killed w o2

Question 13

Where would you expect to find barotolerant and piezophilic microbes? Explain your answer

Answer 13

• Barotoletant: moderate to high pressure because they can survive but are not dependent on pressure for growth
  Barophilic: high pressure because they need it for optimal growth

Question 14

What is a biofilm? List two ways life in a biofilm is advantageous for microbes.

Answer 14

• Complex community of microorganisms attached to a surface with a self produced extracellular polymeric substances (EPS)
  Advantageous because eps protects from environmental stresses and eps is able to trap nutrients

Question 15

What is quorum sensing? Describe how it occurs, and briefly discuss its importance to microorganisms.

Answer 15

• Cell to cell communication
• Microbes produce and release small signaling molecules
  Important for coordinating group behaviours and survival advantages

Question 16

When using direct cell counts to follow the growth of a culture, it may be difficult to tell when the culture enters the death phase. Why?

Answer 16

Direct counting methods cannot differentiate between dead and live cells

Question 17

Why are plate count results expressed as colony forming units?

Answer 17

• Colony can originate from one or many cells
• Not all cells are viable
  Variable growth conditions