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Microbial Nutrition and Growth Microbial Population Growth. Microbiology of the Health Sciences. The Study of Microbial Growth. Growth takes place on two levels Cell synthesizes new cell components and increases in size The number of cells in the population increases

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the study of microbial growth
The Study of Microbial Growth
  • Growth takes place on two levels
    • Cell synthesizes new cell components and increases in size
    • The number of cells in the population increases
  • The Basis of Population Growth: Binary Fission
the rate of population growth
The Rate of Population Growth
  • Generation or doubling time: The time required for a complete fission cycle
  • Each new fission cycle or generation increases the population by a factor of 2
  • As long as the environment is favorable, the doubling effect continues at a constant rate
  • The length of the generation time- a measure of the growth rate of an organism
    • Average generation time- 30 to 60 minutes under optimum conditions
    • Can be as short as 10 to 12 minutes
  • This growth pattern is termed exponential
basic nutrients for growth
Basic Nutrients for Growth

ATP for cellular processes

Carbon is necessary for the

production of many

macromolecules (proteins, lipids,

and carbohydrates)

Oxygen for metabolism

Nitrogen for amino acid synthesis

Sulfur for vitamins, amino acids,

structural stability of proteins

basic nutrients for growth1
Basic Nutrients for Growth

Phosphorous makes ATP and membranes

Trace elements are used for metabolic reaction in the

cell and cell component stabilization

cobalt Co

potassium K

molybdenum Mo

magnesium Mg

manganese Mn

calcium Ca

iron Fe

zinc Zn

basic nutrients for growth2
Basic Nutrients for Growth

Organic growth factors such

as vitamins, amino acids, and

nucleic acids some growth

factors cannot be synthesized

by own cellular processes

Water

water activity

how microbes obtain nutrients
How Microbes Obtain Nutrients

Heterotroph: uses organic

carbon source

Autotroph: uses inorganic

carbon dioxide

Phototroph: uses light as energy

source

Chemotroph: uses chemical

compounds (ie. glucose)

Saprobe

Parasite

culturing microorganisms
Culturing Microorganisms
  • Inoculum introduced into medium (broth or solid)
    • Environmental specimens
    • Clinical specimens
    • Stored specimens
  • Culture – refers to act of cultivating microorganisms or the microorganisms that are cultivated
culturing microorganisms1
Culturing Microorganisms

[INSERT TABLE 6.3]

culturing microorganisms2
Culturing Microorganisms
  • Special Culture Techniques
    • Techniques developed for culturing microorganisms
      • Animal and cell culture
      • Low-oxygen culture
      • Enrichment culture
media
Media

Chemically defined

Natural

Living

media1
Media

Enriched Media

added nutrient encourages

the growth of microorganisms

media2
Media

Selective Media

Selects form a microorganism

while inhibiting most others

Phenol Ethanol Agar

Deoxycholate Agar

media3
Media

Differential Media

Allow for the differentiation of

microorganisms based on

action that occurs on the media

or a color change within the

media that is based on a pH

change

Mannitol Salt Agar

MacConkey Agar

media question
Media Question

What type of media is

Blood Agar considered?

  • Enriched
  • Selective
  • Differential
the population growth curve
The Population Growth Curve
  • A population of bacteria does not maintain its potential growth rate and double endlessly
  • A population displays a predictable pattern called a growth curve
  • The method to observe the population growth pattern:
    • Place a tiny number of cells in a sterile liquid medium
    • Incubate this culture over a period of several hours
    • Sampling the broth at regular intervals during incubation
    • Plating each sample onto solid media
    • Counting the number of colonies present after incubation
the rate of population growth1
The Rate of Population Growth
  • Generation or doubling time: The time required for a complete fission cycle
  • Each new fission cycle or generation increases the population by a factor of 2
  • As long as the environment is favorable, the doubling effect continues at a constant rate
  • The length of the generation time- a measure of the growth rate of an organism
    • Average generation time- 30 to 60 minutes under optimum conditions
    • Can be as short as 10 to 12 minutes
  • This growth pattern is termed exponential
stages in the normal growth curve
Stages in the Normal Growth Curve

Data from an entire growth period typically

produce a curve with a series of phases

  • Lag Phase
  • Exponential Growth Phase
  • Stationary Growth Phase
  • Rapidly Declining Phase
  • Death Phase
lag phase
Lag Phase
  • Relatively “flat” period
  • Newly inoculated cells require a period of adjustment, enlargement, and synthesis
  • The cells are not yet multiplying at their maximum rate
  • The population of cells is so sparse that the sampling misses them
  • Length of lag period varies from one population to another
exponential growth logarithmic or log phase
Exponential Growth (Logarithmic or log) Phase
  • When the growth curve increases geometrically
  • Cells reach the maximum rate of cell division
  • Will continue as long as cells have adequate nutrients and the environment is favorable
  • The number of cells growing greatly out number the number of cells dying.
stationary growth phase
Stationary Growth Phase
  • The population enters a survival mode in which cells stop growing or grow slowly
    • The rate of cell inhibition or death balances out the rate of multiplication
    • Depleted nutrients and oxygen
    • Excretion of organic acids and other biochemical pollutants into the growth medium
    • The number of cells growing will equal the amount of cells dying.
    • Endospores begin to form in this phase.
rapidly declining phase
Rapidly Declining Phase
  • The curve dips downward
  • Cells begin to die at an exponential rate
  • The amount of cells dying out numbers the amount of cells growing.
  • The dead cells become nutrients for the growing cells.
death phase
Death Phase
  • The curve continues to dips downward
  • Most cellular activity stops
  • Endospores are formed and released from the parent cells.
phases of growth
Phases of Growth

Basic phases of growth:

1. Lag phase: new growth medium, period of delay while cells prepare to divide

2. Log phase (exponential growth phase): cellular reproduction most active during this period, generation time reaches a constant minimum

3. Stationary phase: state of equilibrium where number of cell deaths equals number of cell divisions

phases of growth1
Phases of Growth

Basic phases of growth:

4. Rapidly Declining Phase: cells die logarithmically, endospores formed

5. Death phase: number of deaths exceeds number of new cells

potential importance of the growth curve
Potential Importance of the Growth Curve
  • Implications in microbial control, infection, food microbiology, and culture technology
  • Growth patterns in microorganisms can account for the stages of infection
  • Understanding the stages of cell growth is crucial for working with cultures
  • In some applications, closed batch culturing is inefficient, and instead, must use a chemostat or continuous culture system
graphing bacterial growth
Graphing Bacterial Growth
  • The data from growing bacterial populations are graphed by plotting the number of cells as a function of time
    • If plotted logarithmically- a straight line
    • If plotted arithmetically- a constantly curved slope
  • To calculate thesize of a population over time: Nf = (Ni)2g
    • Nf is the total number of cells in the population at some point in the growth phase
    • Ni is the starting number
    • g denotes the generation number