454 



PRINCIPLES OF SOIL MICROBIOLOGY 



in the soil is a result of addition of plant residues, which have resisted 

 decomposition, such as a part of the ligno-cellulose or is a product of 

 the decomposition of complex compounds, such as nucleo-proteins. 

 Fungus mycelium will contain about 1 per cent pentosan even when 

 grown on a pentose-free medium. 



Decomposition of hemicelluloses by microorganisms. Many fungi 

 are capable of decomposing hemicelluloses. These include various 

 species of Aspergillus and other organisms. 82 Certain lower animals 

 are also capable of assimilating hemicelluloses. 83 The hydrolysis of 

 these polysaccharides is carried on by means of an enzyme cytase. u 



TABLE 40 

 Decomposition of pentosans by fungi and by a mixed flora Si 



ORGANISM 



Asp. flavus 



Asp. fumigatus. . . 



Asp. niger 



Asp. oryzae 



Asp. repens 



Pen. glaucum 



Cvnninghamella sp 

 Rhizopus nigricans 

 Soil suspension . . . 

 Cow feces 



Schmidt, Peterson and Fred 85 tested the pentosan decomposing 

 power of a number of different fungi, by adding 1 gram of corn stover 

 or rye straw to 25 cc. of a nutrient mineral solution containing NH 4 N0 3 

 as the only source of nitrogen. Different organisms were found to 

 vary in their ability to decompose pentosans. It is interesting to note 



82 H6rissey, H. Recherches chimiques et physiologiques sur la digestion des 

 mannanes et des galactanes par le seminase chez les vegetaux. These. Paris. 

 1903. Schellenberg, 1908 (p. 264). Otto, 1916 (p. 265). 



83 Bierry, H., and Giaja, J. Untersuchungen liber die Mannane, Galaktine 

 und Zellulosen-angreifenden Enzyme. Biochem. Ztschr., 40: 370. 1912. 



84 Newcombe, F. C. Cellulose-enzymes. Ann. Bot., 13: 49-81. 1899. 



86 Schmidt, E. G., Peterson, W. H., and Fred, E. B. The destruction of pento- 

 sans by molds and other microorganisms. Soil Sci., 15: 479-488. 1923. Ver 

 Hulst, Peterson and Fred, 1923 (p. 452). 



