RELATION OF AZOTOBACTER TO OXYGEN 6$ 



Exercise 30 



Effect of Variation in Culture-media on the Growth of 



Azotobacter (Optional) 



1. Prepare eight tubes of agar slopes. 



2. Arrange the culture-media as follows: 



(a) I and 2, mannit agar. 



(6) 3 and 4, agar without mannit. 



(c) 5 and 6, agar with lactose in place of mannit, 



(d) 7 and 8j mannit agar without phosphate. 



3. Inoculate all cultures from a suspension of Azoto- 

 bacter. 



4. Incubate at 28^ C. Examine every two days for 

 twelve days or longer. 



5. Record the growth of Azotobacter on the various 

 culture-media. 



Exercise 31 



Relation of Azotobacter to Oxygen 



1. Prepare six mannit agar slope cultures of Azotobacter 

 chroococcum. 



2. Treat as follows: 



(jn) I and 2, untreated. 



(6) 3 and 4, place in an atmosphere free of oxygen (see page 133). 

 (c) 5 and 6, seal the tubes by melting the glass and drawing out the 

 ends. 



3. Incubate at room temperature. 



1 Examine weekly for ^owth and pigment formation. 

 If the sealed tubes fail to show a brown to black pigment 

 after two weeks, open "and note the change in color after 

 three or four days. 

 5 



