GREEN FLUORESCENT BACTERIA FROM WATER 75 



Starch destruction 



No official method for determining the presence of diastase 

 is available, and each worker uses his own favorite technique. 

 The method used by Edson and Carpenter required the addition 

 of 2 per cent thymol starch paste to a ten day old broth culture. 

 After incubation for eight hours the culture was filtered and 

 tested for reducing sugar by means of Fehling's solution. 



The method suggested by Smith was used in this work, as 

 outlined by Harding (1910). Cultures of the bacteria were 

 grown on potato slants for ten days at 37 °C. At the end of 

 this time these slants were crushed in a mortar together with 

 the water in the bottom of the culture tubes. This mixture 

 was diluted with distilled water and tested with a weak solution 

 of iodine in potassium iodide for the split products of starch. 

 If the starch mixture had not been sufficiently diluted the blue 

 color which this substance gives with iodine would have entirely 

 masked the color given by some of the decomposition products. 

 The presence of erythrodextrin is shown by a red color. Good 

 results may be obtained with this method after one has become 

 accustomed to the color changes which are involved. Starch 

 agar plates were also used. These were made by adding 1 cc. 

 of a sterile 2 per cent solution of soluble starch to plain agar in 

 Petri dishes. Streaks of the pure culture were made upon this 

 medium and the plates incubated at 37° for five days. At the 

 end of this period a dilute solution of iodine in potassium iodide 

 was permitted to flow over the surface of the plate. With those 

 bacteria which decompose starch a colorless area will be noted 

 about the line of growth. None of the cultures studied were 

 able to decompose starch. This is perhaps not to be expected 

 when one recalls the strong proteolytic action of this group. 

 Over 50 per cent of the cultures were able to break down gelatin, 

 as reported by other investigators. 



Agar colonies 



Colony growth on agar was always abundant. After the 

 colonies were well developed a large amount of soluble pigment 

 was formed. The edge was always irregular and rarely entire. 



