Christine Case, Skyline College

Winogradsky Column
Photo©CLCase

Environmental Microbiology
Experiments for middle and high school

Christine L. Case
and
Patricia Carter
Skyline College

Laboratory Safety
List of experiments

Chocolate fermentation
A note to teachers:
It is no exaggeration to say that without microbes the familiar forms of life could not exist. All life is dependent upon the "services" performed by these invisible organisms. One of the most important of these services is to provide the energy needed to carry out the metabolic activities necessary to all living organisms. Microbes are essential for the recycling of elements so they can be used over and over again. The cycles of elements are called biogeochemical cycles. In the carbon cycle, carbon atoms are transferred from organism to organism. Carbon dioxide is incorporated into organic compounds by photoautotrophs (e.g., bacteria, algae, plants), and these organic compounds are digested by chemoheterotrophs (e..g., animals, fungi, bacteria), which release carbon dioxide in respiration and fermentation to be reused by photoautotrophs. Bacteria have essential roles in the nitrogen cycle. All organisms require organic molecules containing nitrogen atoms, but only certain bacteria can convert nitrogen in the atmosphere to forms that are accessible to other organisms. Without the nitrogen-fixing activities of these bacteria, nitrogen would eventually become locked up in the atmosphere and life as we know it would cease.

Ecology is the study of the interrelationships of organisms with each other and with their environment. Therefore, natural populations of microorganisms are used in the experiments in this manual. For years, microbiology focused on isolating pure cultures of microbes. We are now beginning to understand that many of the bacteria in natural communities cannot be cultured because of special physical or chemical requirements. Bacteria can be used to eliminate toxic wastes, this is called bioremediation. No single microbe can do this, instead, a succession of bacteria, each modifying the chemical for the next microbe, is necessary to eliminate the toxic substance and return a harmless or useful substance to the environment.

Bacteria and humans have similar enzymes and metabolic systems. Laboratory experiments using microbiologic examples can provide your students with an opportunity to do actual experiments and to understand their own metabolism. These laboratory experiments allow students to use the scientific method, measure in metric units, and be involved in a practical application of science. Predicting results and waiting for the cultures to grow to prove or disprove your predictions is exciting for teachers as well as students.

The laboratory experiments presented in this manual have minimal supply needs-most do not require microscopes or other equipment. The bacteriologic culture media that are required can be purchased from biological supply houses such as Carolina Biological Supply, Ward's Natural Sciences, or Hardy Media. Please check with your local college, hospital lab, public health lab, water treatment plant lab, or wastewater treatment facility lab; these agencies are often willing and able to supply culture media.