378 PRINCIPLES OF SOIL MICROBIOLOGY 



When a fresh amount of undecomposed organic matter is added to 

 the soil, a rapid increase in numbers of microorganisms takes place 

 because a large amount of the energy added is readily available. 



Microorganisms are not, however, constant in composition. They 

 vary with the composition of the medium and adapt themselves to the 

 available nutrients. Cramer 20 found that the average water content 

 of bacteria grown on agar media was 87.71 per cent. The dry material 

 consisted of 50.47 to 51.81 per cent carbon, G.59 to 7.49 per cent hy- 

 drogen, 12.32 to 13.46 per cent nitrogen and 7.79 to 10. 3G per cent ash. 

 On media rich in carbohydrate the nitrogen content was often less than 

 10 per cent. The alcohol ether extract varied from 9.06 to 24.0 per 

 cent, depending on the organisms and the composition of the medium. 



According to Nicolle and Alilaire, 21 bacteria contain, on the basis of 

 dry weight of cells, 8.3 to 10.8 per cent of nitrogen. The moisture 

 content of the cells varied from 73.4 to 85.5 per cent; acetone extracted 

 6.3 to 15.6 per cent of the dry material and chloroform 1.5 to 11.8 per 

 cent. The phosphorus content of the chloroform extract varied from 

 0.2 to 2.5 per cent. 22 



Algae grown on synthetic nutrient agar media with Ca(N0 3 )2 as the 

 only source of nitrogen were found 23 to contain 7.4 per cent nitrogen, 

 on an ash-free basis. About 25 per cent of this nitrogen could be 

 extracted with water and consisted of proteins, amino acids and pep- 

 tides. The nitrogen content of fungi was found 24 to vary between 2.3 

 and 6.6 per cent, depending on the nature of substrate. Soon after 

 the spores germinate and active cell formation takes place, the 

 nitrogen content of the fungi may be much higher. 25 A study of the 

 nitrogen content of bacteria, fungi and actinomyces, grown on media 

 containing an amino acid as the only source of carbon and nitrogen, 



20 Cramer, E. Die Zusammensetzung der Bakterien in ihrer Abhiingigkeit 

 von dem Nahrmaterial. Arch. Hyg., 16: 151-195. 1893. 



21 Nicolle, M., and Alilaire, E. Note sur la production en grand des corps 

 bacteriens et sur leur composition chimique. Ann. Inst. Past., 23: 547-557. 1909. 



22 Further information on the composition of the bacterial cells is given by 

 Kruse, 1910 (p. xii). 



23 Fred, E. B., and Peterson, W. H. Forms of nitrogen in pure cultures of 

 algae. Bot. Gaz., 79: 324 328. 1925. 



24 Maze, P. Recherches sur les modes d'utilisation du carbone ternaire par 

 les vegetaux et les microbes. Ann. Inst. Past., 16: 346-378. 1902. 



25 Nikolsky, M. tlber den Einfluss der Nahrung von verschiedenen Kohle- 

 hydraten auf die Entwicklung der Schimmelpilze. Centrbl. Bakt. II, 12: 554- 

 559, 656 675. 1904. 



