- Identify the reactions associated with growth on skim milk agar
The enzyme caseinase is secreted out of the cells (an exoenzyme) into the surrounding media, catalyzing the breakdown of milk protein, called casein, into small peptides and individual amino acids which are then taken up by the organism for energy use or as building material. The hydrolysis reaction causes the milk agar, normally the opacity of real milk, to clear around the growth area as the casein protein is converted into soluble and transparent end products—small chains of amino acids, dipeptides, and polypeptides.
- 1 skim milk agar plate per table
- Run this test using your unknown bacterium.
- Inoculate the organism on the plate either a straight line or a zig-zag.
- Incubate at 25º C or 37º C.
- Record the results of your bacterial unknown in your journal.
- What is the difference in a weak + and a strong + reaction on the agar plate?
- The substrate for this enzyme is _____.
Contributors and Attributions
Jackie Reynolds, Professor of Biology (Richland College)