SOURCES OF ENERGY FOR THE AZOTOBACTER 263 



naturally occurring glucosides and many henzin derivatives are 

 unsuitable as sources of energy for Azotobacter. Molasses, which 

 should serve as a useful source of energy, often results in a loss of 

 nitrogen when applied to the soil. This may be due to the time of 

 applying, for Peck maintains that molasses applied to a land lying 

 fallow at an interval of several weeks before planting of the crop 

 may produce beneficial results by increasing nitrogen-fixation. 



Beijerinck early recognized that certain decomposition products 

 of cellulose can also serve as sources of energy for Azotobacter, and 

 Pringsheim found that Clostridium americanum does not fix atmos- 

 pheric nitrogen on sterilized cellulose unless other carbohydrates 

 like dextrose, lactose, mannitol, or sucrose are present. However, 

 in the presence of cellulose, Clostridium will fix nitrogen and this 

 more efficiently than it will in the regular carbohydrate medium. 

 The same holds for agar. Just how completely cellulose must be 

 broken down before it can be utilized by Azotobacter is not definitely 

 known, but it is known that Azotobacter cannot utilize cellobiose 

 except when grown in conjunction with Aspergillus niger or other 

 organisms. It is, therefore, certain that the products which are 

 utilized by the Azotobacter are comparatively simple. 



Cellulose when applied to the soil may serve as a valuable source 

 of energy, provided sufficient time is allowed for its decomposition. 

 The cellulose ferment is probably the most efficient organism in the 

 soil in bringing about this decomposition. But the number of soil 

 fungi which possess this power is large. 



Hoppe Seyler thinks that cellulose is decomposed according to the 

 following formula: (a) the hydration of the cellulose with the 

 formation of hexose, 



=C 6 Hi 2 O 6 . 



the destruction of the carbohydrate with the formation of equal 

 quantities of carbon dioxid and methane. 



None of the cellulose ferments studied by McBeth, however, yielded 

 gaseous products when acting on cellulose or sugar; hence the 

 Azotobacter probably gets from the cellulose ferments, pentoses 

 and hexoses, and similar products upon which they can readily fix 

 nitrogen. 



At times in fermenting straw and manure, the thermophilic 

 anaerobic bacteria play a major part, in which case fatty acids 

 probably make up the greater part of the end products. 



It is claimed by Dvarak that substances with low carbon and high 

 oxygen content are usually the best sources of energy for A. chroo- 

 coccum, which assimilated 5.73 mgm. of free nitrogen per 100 gm. 

 of carbon in pine leaves as compared with 1237.9 rngm. per 100 gm. 



