MicrobiologyBytes: Introduction to Microbiology: Microbiology Techniques Updated: January 28, 2007 Search

Techniques of Microbiology

Microbiology as a discipline is defined by the techniques used to study microorganisms!

Microbiology encompasses the study of:

The Techniques:

  1. Microscopy and stains: electron microscopy.
  2. Sterilization - look at your practical book!
  3. Getting a pure culture : aseptic technique + sterile media:
  4. Composition of culture media, temperature of incubation, osmotic potential of media, pH etc.
  5. Anaerobe or aerobe? - microaerophile?

Nutitional Types:

Major Nutritional Types: Sourges of Energy, Hydrogen/Electrons, Carbon: Representative Microorganisms:
Photolithotrophic autotrophy: Light energy
Inorganic hydrogen/electron (H/e-) donor
CO2 carbon source
Algae; purple & green sulphur bacteria; blue-green bacteria (Cyanobacteria)
Photoorganotrophic heterotrophy: Light energy
Organic (H/e-) donor
Organic carbon source (CO2 may also be used)
Purple non-sulphur bacteria; green non-sulphur bacteria
Chemolithotrophic autotrophy: Chemical energy source (inorganic)
Inorganic (H/e-) donor
CO2 carbon source
Sulphur-oxidizing bacteria; hydrogen bacteria; nitrifying bacteria; iron bacteria
Chemoorganotrophic autotrophy: Chemical energy source (organic)
Organic (H/e-) donor
Organic carbon source
Protozoa; fungi; most nonphotosynthetic bacteria


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Bacterial Growth:

The bacterial growth curve:
  1. Lag phase
  2. Exponential phase
  3. Stationary phase
  4. Death phase

During the exponential phase, the number of cells doubles every generation (1, 2, 4, 8, 16...) and the number of cells in the culture (Nf) at any particular time is given by:

Nf = (Ni)2n


Ni is the initial size of the population
n is the number of generations that have elapsed.

This equation is usually written in the form log10 for mathemetical convenience:

log10Nf = log10Ni + 0.301n(log10 2 = 0.301)

From this equation it is possible to ddetermine n (generations elapsed) by knowing the numbers of cells at the beginning and end of a particular incubation period:

n = (log10Nf - log10Ni) / 0.301

This is useful because it enables calculation of the generation time g (the time between the beginning and end of the incubation period:

g + t/n = 0.301 / (log10Nf - log10Ni)

Online Experiment: The Bacterial Growth Curve
Determine the rules which control bacterial growth.

by L.M.Prescott et al.
A balanced, comprehensive introduction to all major areas of microbiology. The sixth edition has been updated extensively to reflect the latest discoveries in the field.

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