Bacterial Growth

OBJECTIVES

  • describe the essential steps in cell division during binary fission in bacteria
  • draw a growth curve and explain what is occuring during the growth cycle of a bacterial population in batch culture
  • use the growth equation to calculate generation time, growth rate, and populations of bacterial cells during logarithmic growth
  • distinguish between generation time, growth rate and yield
  • explain the population dynamics of bacterial growth in a chemostat
  • apply knowledge of bacterial growth to environmental growth, industrial use of bacteria, and appropriate use of antibiotics

HOW DO BACTERIA REPRODUCE?

  • Binary fission
  • Budding
  • Fragmentation

What occurs during binary fission?

  • DNA duplication
  • DNA repication
    • single origin of replication, bidirectional
    • theta intermediate
  • Separation of DNA and cytoplasmic contents
  • Cross wall formation

Generation time - doubling time

  • time from one reproduction to another
  • 1 to 2 or 100 to 200 or 1 million to 2 million
  • Is generation time identical for all bacteria?
  • Is it always the same for a single bacterium?
  • Growth rate - no. doublings per hr (inverse of generation time)
  • How does growth rate influence clinical diagnosis? disease progression?

Mycobacterium tuberculosis (in lab)

12 hrs

Clostridium botulinum (in lab)

0.58

E. coli (in lab)

0.30

E. coli (in mouse)

20 hrs

What happens when you inoculate a single bacterium from slant stored in refrigerator into nutritional medium and incubate?

  • Why doesn't it grow immediately?
  • What determines how fast it grows?
  • Why does it stop growing?

Phases in bacterial growth in batch culture

Growth yield is the amount of cells produced at end of exponential growth

GROWTH EQUATION: Log Bf = LogBi + .3t/dt

PRACTICE PROBLEM: A culture is inoculated at noon with 103 cells/ml. At 10 pm the population is determined to be 109 cells/ml. What is the doubling time?

HOW CAN MICROBES BE KEPT IN THE LOG PHASE?

WHAT FACTORS AFFECT GROWTH?

  • Nutrients - Cell constituents and energy sources
  • Physical factors - temp, pH, water, oxygen, pressure

ELEMENT

CELL FUNCTION

C

organic cell components, energy

H

water, organic components

O

water, organic components, respiration

N

amino acids, nucleotides, coenzymes

S

amino acids, coenzmyes, enzymes

P

nucleic acids, phospholipids, coenzymes, ATP

Fe

cytochromes, enzymes

Na, K, Ca, Cl, Mg, Mn

transport, ionic balance

Describe three ways in which our current knowledge of encouraging microbial growth affects something in your life and three ways in which our current knowledge of interfering with microbial growth affects something in your life.

Define and distinguish between growth rate and generation time.

Using the equation log10Bf = log10Bi + 0.3t/gt (on page 116 ), determine the following:

B. prepared is a bacterium isolated from the brows of microbiology students studying for Dr. Kandel's next quiz. What is its doubling time if it takes 3 hours to go from 103 cells/ml to 1012 cells/ml?

Draw and label a typical bacterial growth curve in batch culture.

a) What is occuring in each stage?

b) What factors limit microbial growth in batch culture?

c) How and for what purposes are microbes maintained in log phase in a chemostat?

d) How do you know if a bacterium is dead?

Define optimal growth.

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