Omnipresence of Microorganisms in the Environment


This procedure was adapted from A Laboratory Manual for Microbiology, third edition, by John M. Larkin.

Microorganisms are ubiquitous in our environment. Practically any area of the earth is inhabited by a micro ecosystem of life forms that may be uniquely adapted to that environment.


All living cells share certain requirements for growth. C, H, O, N, P and S are the elements considered basic for cell growth. Water is essential for growth, since it comprises approximately 70% of the cell. Molecular oxygen is essential for the growth of many but not all cells. All cells have a need for energy, which may be obtained by trapping sunlight and converting light energy to chemical energy, or by releasing the chemical energy contained in bonds within compounds.

This experiment will demonstrate the numbers and diversity of microorganisms found in the environment. It will utilize the concepts of growth requirements and demonstrate the use of a selective medium. Two media which support the growth of organisms commonly found in the environment are utilized.


Nutrient agar contains


Sabouraud agar contains

Nutrient agar is one of the most widely used media in microbiology. The Sabouraud agar is a selective medium, which is a culture medium designed to suppress the growth of unwanted microorganisms and encourage the growth of desired ones. The lower pH of the Sabouraud agar inhibits the growth of most bacteria, making it selective for yeasts and fungi. Inoculation from the same environmental site onto the two media should readily demonstrate the bacterial versus fungal flora of the site.


Materials per pair of students: