462 PRINCIPLES OF SOIL MICROBIOLOGY 



formation of acids, alcohols and acetone. 109 In this, the action of 

 bacteria upon starch may be distinct from that of diastatic enzymes, 

 which give 100 per cent maltose, and from the acid hydrolysis of starch, 

 which results in the formation of glucose. 



The number of organisms in the soil capable of hydrolyzing starch 

 can be readily determined. The soil is diluted 1:1000 to 1:200,000. 

 The final dilution is plated out on a medium which consists of 15 grams 

 potato starch, 1 gram of an organic or inorganic source of nitrogen, 

 0.5 gram K2HPO4, 15 grams of agar and traces of MgS0 4 and FeCl 3 

 in 1000 cc. of water. After a few days incubation (3 to 7), the plates 

 are covered with a dilute solution of iodine and potassium iodide. The 

 colonies of the microorganisms producing diastase will be surrounded 

 with a clear zone; these colonies may then be counted. A number of 

 bacteria are capable of decomposing starch, including various spore 

 forming organisms, such as Bac. subtilis, Bac. mesentericus, Bac. cereus 

 and other common soil bacteria, and also various species of Bac. amy- 

 lobacter. Certain non-spore bearing bacteria, such as certain cellu- 

 lose-decomposing organisms and others, are also capable of decom- 

 posing starch. The ability to hydrolyze starch is widely distributed 

 among fungi, such as Asp. oryzae, Asp. nigcr and Amijlomyces boidin. 



Formic, acetic and butyric acids, traces of lactic and succinic acids, 

 various alcohols (ethyl and butyl), aldehydes and acetone, hydrogen 

 and carbon dioxide have been obtained among the products of decom- 

 position of starches by microorganisms. Bac. mesentericus, for example, 

 breaks down starches into carbon dioxide, formic and valerianic acids. 

 Bac. granulobacter pectinovorum growing in media rich in starch changes 

 the starch into glucose by means of enzymes; the sugar passes into the 

 cell and is oxidized to acetic and butyric acids, a part of which is re- 

 duced to the corresponding alcohols. 110 



Inulin, similar in its properties to starch, but giving levulose on 

 hydrolysis, can also be decomposed by various bacteria and fungi. 111 



109 Schardinger, F. Bacillus macerans, ein Aceton-bildender Rottebacillus. 

 Centrbl. Bakt. II, 14: 772-781. 1905; Zur Biochemie des Bacillus macerans. 

 Ibid., 19: 161-163. 1907; 22: 98-103. 1909; 188-197. 1911. For further in- 

 formation on this subject, consult Pringsheim, 1923 (p. 427). 



110 Speakman, H. B. Biochemistry of the acetone and butyl alcohol fermenta- 

 tion of starch by Bacillus granulobacter 'pectinovorum. Jour. Biol. Chem., 41: 

 319-343. 1920. 



111 Grafe, V., and Vouk, V. Das Verhalten einiger Saccharomyzeten (Hefen) 

 zu Inulin. Ztschr. Garungsphys., 3: 327-333. 1913; Kiesel, A. L'influence 

 de la reaction du milieu sur Taction de l'inulase de l'Aspergillus niger. Ann. 

 Inst. Past., 28: 747-757. 1914. 



