BACTERIA DECOMPOSING CELLULOSE 



85 



available forms to permit the microbes to use the cellulose as food. 

 Phosphorus is required in greater amounts than any of the other 

 mineral substances, and may comprise two-fifths of the total ash 

 of microbial cells. However, phosphorus (calculated as P) may 

 be required for the synthesis of cells in only about one-tenth the 

 amounts that nitrogen is needed. Other minerals are required in 

 much smaller quantities. 



Bacteria Decomposing Cellulose. — The bacteria decompos- 

 ing cellulose can be divided conveniently into two groups, repre- 

 sentatives of which differ considerably in their morphological 

 characters and physiological activities: (1) aerobic bacteria and 

 (2) anaerobic bacteria. Among the aerobic forms there are spore- 

 forming and non-spore-forming rod-shaped bacteria, spherical 

 organisms and spirochaete-like or flexuous organisms (see Fig. 8). 

 It is characteristic of all that free atmospheric oxygen is re- 

 quired for development, just as in the case of the cellulose- 

 decomposing fungi, but, while the fungi will grow readily in very 

 acid soils of a pH 4.0 and even less, the aerobic bacteria will not 

 grow at an acidity greater than pH 5.6-6.0, as shown in Table 21. 



TABLE 21 



Effect of Reaction of the Soil on the Number of Cellulose- 

 Decomposing Bacteria (from Dubos) 



Neither fungi nor aerobic bacteria will grow in marshes or 

 undrained peat soils which are anaerobic in nature. In forest, 

 field, and garden soils, both groups of organisms will develop, the 

 reaction of the soil determining the group that will predominate. 

 Soils more acid than pH 5.5 will show largely a flora of fungi which 

 will be the active agents in cellulose decomposition; soils less acid 



