4 Dynamics of Microbial Growth

binary fission

Bacteria growth is measured by the number of cells.

Done through __: asexual reproduction in which one cell divides to form two identical daughter cells

Growth is exponential → population doubles with each division

N_t = N₀ × 2ⁿ ,

wherein

• N_t = number of cells at a given time (t)

• N₀ = initial amount of cells

• n = number of generations at that point in time*

  • (*) must account for Generation time

Generation time

Speed of bacterial growth depends on

__: time taken for a cell to divide or population to double

• varies from species to species

• also dependent on environmental conditions

  • nutrient-rich mediums = faster time

  • ideal temperature of growth affects speed

    • eg. E. coli normally grows at 37 degrees Celsius

10 days

Mycobacterium leprae has a generation time of __

Treponema pallidum

Organism that causes syphilis. Has a generation time of 33 hours

33 hours

Treponema pallidum (causes syphilis) has a generation time of __

12 hours

Mycobacterium tuberculosis has a generation time of __

chronic

Since Mycobacterium tuberculosis has a generation time of 12 hours,

TB (the disease it causes) is considered a __ disease, as it takes a long time to develop

20 minutes

Escherichia Coli has a generation time of __.

Pure culture

Population of cells derived from a single cell.

Clones; genetically identical

aseptic technique

How pure culture is maintained; set of procedures used to minimize potential contamination

Culture medium

Where bacteria is grown in or on

Contains nutrients dissolved in water

can be:

• broth: liquid media

• solid gel: broth media with the addition of agar

Agar

Marine gel extract that is added to broth to turn it into solid media

• liquefies/melts at >95 degrees Celsius

  • boil to revert back to broth

• solidifies at 45 degrees Celsius

  • solid at room temperature and body temperature

  • remains solid over entire temp. range most microbes grow

Petri dish

Two ways to grow bacteria on solid agar

• slant: agar in a tube solidified at an angle → angle gives more SA for bacteria to grow

• __: agar plate → ideal amount of large SA where bacteria can grow into colonies: distinct masses of cells

  • note: ~1 million bacteria already grown if it’s macroscopic to the eye

Streak-plate method

Simplest and most commonly used technique for isolating bacteria

Successive streak patterns used to sequentially dilute an inoculum on the surface of an agar plate

→ spreads out cells into isolated colonies

w/ goal: retrieving a pure culture

closed system

Bacteria grown on agar plates / tubes / flasks of broth are __(s)

i.e, batch cultures

• what is inside stays inside

• nutrients not renewed; wastes not removed. hence it is a __!

  • running low on nutrients / inc. waste → stops growth on own

Growth Curve

Batch cultures demonstrate this characteristic pattern of bacterial growth and decline due to its limited resources

• lag phase: cell number doesn’t increase. bacteria preparing for growth

• log / exponential phase: where cells grow as quickly as possible

  • most sensitive to antibiotics in this phase (penicillin!)

  • energy is spent on growing rather than surviving

• stationary phase: number of cells produced = cells dying (equilibrium). overall population stabilizes

  • happens from exhausted nutrients or waste build up

• death phase: total number of viable cells decreases. death is exponential

• phase of prolonged decline: 99% of cells are dead

  • gradual decrease in viable cell population

  • most adapted cells survive

lag phase

1/5 distinct stages in the Growth Curve

Cell number doesn’t increase. Bacteria preparing for growth

exponential phase

2/5 distinct stages in the Growth Curve

When cells grow as quick as possible. Also known as log phase.

• sensitive to antibiotics as energy redirected to growth, not survival

• penicillin especially effective → targets peptidoglycan synthesis

3/5 distinct stages in the Growth Curve

4/5 distinct stages in the Growth Curve

5/5 distinct stages in the Growth Curve

extremophiles

Prokaryotes that live harsh environments

primarily of Archaea domain

Temperature

¼ environmental factors that influence growth

This is because each species has a well defined __ range » optimum growth [_]

Prokaryotes divided into 5 categories by these ranges:

• Psychrophiles (-5 to 15 C)

• Psychrotrophs (20 to 30 C)

• Mesophiles (25 to 45 C)

• Thermophiles (45 to 70 C)

• Hyperthermophiles

Oxygen

2/4 environmental factors that influence growth

pH

¾ environmental factors that influence growth

water availability

4/4 environmental factors that influence growth