200 PRINCIPLES OF SOIL MICROBIOLOGY 



bacterium is 2 by 0.5 to 0.7^ with coccoid forms of 0.5 to 0.7^, motile with a single 

 flagellum. The addition of dextrin, lignin, xylose and certain sugars stimulated 

 cell development. 26 



Decomposition of cellulose by denitrifying bacteria. Certain bacteria 

 are able to decompose cellulose and utilize the energy for the reduction 

 of nitrates to nitrites. A medium containing 0.25 gram KN0 3 , 0.05 

 gram K 2 HP0 4 and 2 grams of cellulose in the form of filter paper in 

 100 cc. of tap water can be used. 27 This medium is placed in a glass 

 stoppered flask up to the neck, inoculated with canal slime and incu- 

 bated anaerobically at 35°. Cellulose decomposition begins in a week 

 and is accompanied by reduction of nitrate to nitrite. The nitrite also 

 disappears in 15 days. On renewing the medium, the process of nitrate 

 reduction is greatly hastened. The cellulose becomes orange yellow 

 and of a slimy consistency. It is broken down into fibers which finally 

 disappear. The gases consist of a mixture of nitrogen and carbon diox- 

 ide. No organism responsible for the process of cellulose-decomposi- 

 tion could be isolated from the mixture of various bacteria and protozoa. 



Groenewege, 28 using a medium which consisted of 20 grams filter paper, 

 2.5 grams KN0 3 and 0.5 gram K 2 HP0 4 in 1000 cc. water and inoculated 

 with soil, found that the process of cellulose decomposition by denitrify- 

 ing bacteria is carried on by the symbiotic action of two groups of 

 organisms, one of which decomposes the cellulose and the other of which 

 uses the products formed as a source of energy for the reduction of 

 nitrates. By the symbiotic action of the two organisms the cellulose 

 disappears much more rapidly than by the action of the cellulose organ- 

 ism alone. Gas formation began to take place on the second day, 

 accompanied by a reduction of nitrate to nitrite and NO with a gradual 

 dissolution of the paper. The process was especially active when the 

 culture solution was renewed by decantation. 



To stimulate the development of cellulose-decomposing organisms, 

 Van Iterson buried filter paper in the soil and after four weeks found 

 that it became almost entirely decomposed and covered with orange and 

 black spots. The black spots consisted of fungi. Using this material 

 for inoculation, a complete reduction of 0.6 per cent KN0 3 took place 

 in three days. On replacing the solution by decantation, complete 

 denitrification may take place in twenty-four hours. The organisms 

 responsible for the process were obtained in pure cultures by the use of 



27 Van Iterson, 1904 (p. 195). 



28 Groenewege, J. Untersuchungen liber die Zersetzung der Zellulose durch 

 aerobe Bakterien. Bull. Jard. Bot. Buitcnzorg. 2, f. 3: 261-345. 1920. 



