Microbiology

Fantastic web site with large collection of photos, videos, and text/

Organisms for bioconversions

Click to learn about shapes and some terms.

The exercise applet shows the number of cells versus time after inoculation.

Some terms defined

During the first period, as the organisms acclimate to their new environment, numbers may actually decline. This is called the lag phase. Next the cells numbers increase, the rate of division increases in an autocatalytic fashion. This is termed the logarithmic growth phase, then as nutrients are exhausted, growth declines drastically resulting in a state called the stationary or resting phase. This may be followed by death, with a drop in numbers of viable organisms; however a count that does not distinguish between living and dead cells might fail to detect the death period. Eventually organisms will lyse and no longer resemble living cells.

Math introduction.

A possible relationship between specific growth rate coefficient and substrate concentration is shown as a RED line in the next figure. The white line is for a nutrient that is inhibitory at higher concentrations.

The curve is nearly linear at low concentrations and levels off for high concentrations. If the nutrient reaches toxic levels, the curve may drop precipitously. Except in very rare cases when all nutrients are in perfectly equivalent proportions, one will be present in low ratio to the others. As cells multiply, this ingredient will run out first and will limit further growth. This concept of a growth-limiting nutrient in shortest supply is crucial to understanding microbial processes.

 Some stuff about bacteriophage in our archive.

The following links that are not boldface are in a great archive called Cells Alive:

 Bacteriophage
 Motility, how microorganisms move
Interactive motility Applet
Another great site for mobility
 Division, multiplication of bacteria
 Relative sizes of microorganisms
 Yeast

  • More details of cell structure, then environmental microbiology
  • Some math. 
    The following are supplemental pages. You need not view them unless they are assigned.
  • Cultures
  • Mitosis
  • Doubling time
  • Diauxie 
  • Monod equation  
  • Microbiology of waste treatment