23 
Exercise 11. Enzyme Production by Microorganisms 
MATERIALS: 
Garden soil suspension 
5 tubes of plain agar 
5 tubes of starch agar 
5 tubes of sterile milk 
4 tubes of sterile gelatin 
Pure cultures of bacteria 
Sterile pipettes 
10 sterile Petri dishes 
A. Carbohydrate Hydrolyzing Enzymes icarbohydrases) 
Amylase. 
1. Melt the starch agar and cool to 45° C. 
2. Label five sterile Petri dishes as follows: 
(a) Starch agar, soil suspension. 
(b) Starch agar, pure culture 1. 
(r) Starch agar, pure culture 2. 
( d) Starch agar, pure culture 3. 
(e) Starch agar, B. graveolens culture. 
3. By means of a sterile pipette place a drop of soil suspension in Petri 
dish (a). 
4. Immediately pour starch agar into all of the Petri dishes being care¬ 
ful to observe the precautions indicated in Exercise 8. 
5. When the agar is solid inoculate the four remaining dishes with the 
organisms indicated. Use the straight needle and make the inocula¬ 
tion at one spot in the center of the dish. 
6. Incubate the cultures inverted at room temperature for 48 hours. 
B. Protein Hydrolyzing Enzymes (protelnases) . 
Caseinase 
1. Label five Petri dishes as follows: 
(a) Milk agar, soil suspension. 
( b ) Milk agar, pure culture 1. 
(c) Milk agar, pure culture 2. 
( d) Milk agar, pure culture 3. 
(e) Milk agar, B. graveolens culture. 
2. With a sterile pipette, place one cc. of sterile milk in each of the 
Petri dishes. 
3. By means of a sterile pipette place a drop of soil suspension in Petri 
dish (a). 
4. Melt five tubes of plain agar and cool to 45° C. 
5. Immediately pour agar into all of the Petri dishes being careful to 
mix agar and milk until the whole has a uniform white appearance. 
6. When the agar is solid, inoculate the agar at one point in the center 
of each dish. Use the straight transfer needle, and make inoculations 
as designated in paragraph A5. 
7. Incubate the cultures inverted at room temperature for 48 hours. 
