MICROBIOLOGY OF SOIL 



been confirmed by other investigators, by means of mixtures and single 

 species of soil bacteria. Finally it should be added here that B. 

 oligocarbophilus previously isolated by Beijerinck and Van Delden is 

 able, according to Kaserer, to oxidize also carbon monoxide. 



The Cleavage and Fermentation of Sugars, Starches and Gums. 

 Sugars (page 233) are a very acceptable source of food and energy 

 for soil bacteria. A culture solution containing suitable mineral 

 salts and sugar ferments readily when inoculated with a small amount 

 of fresh soil. When no combined nitrogen is added, Azotobacter, or B. 

 (Clostridium) pasteurianus (or both), may come to the fore. The cleav- 

 age products then include alcohols, organic acids and carbon dioxide. 

 With B. (Clostridium) pasteurianus butyric acid is one of the prominent 

 cleavage products. When combined nitrogen is also added to the 

 culture solution other organisms will develop prominently, notably 

 members of the subtilis group, butyric bacteria, aerogenes, etc. In the 

 soil itself the addition of sugar leads to a very marked increase in 

 number and, if acid production is favored, molds may subsequently 

 become prominent. In general it may be said that butyric, propionic, 

 acetic, formic and lactic acid, and ethyl, propyl, butyl and iso-butyl 

 alcohol are common cleavage products. 



In the case of starch, pectins and pentosans, similar conditions hold 

 good. Diastatic enzymes seem to be produced by various bacteria 

 as well as by molds and actinomycetes. Members of the subtilis group 

 and B. Huorescens seem to be able to transform starch into sugar with- 

 out difficulty. It needs hardly be added here that the vast quantities 

 of organic acids and of carbon dioxide thus formed must play an im- 

 portant role in the breaking down of the mineral constituents in the 

 soil. 



FATS AND WAXES 



Origin and Decomposition. Plant substances contain varying 

 proportions of fats and waxy materials. In the dry matter of grasses 

 and cereal straw crude fat is usually present to the extent of 1.5 to 

 2.0 per cent. In hay made from clover and other legumes the propor- 

 tion of crude fat is rather more than 2 per cent. In cereal grains it 

 may range up to 4 or 5 per cent while in soy beans the content of 

 crude fat is 19 per cent, in germ oil meal 22 per cent and flax seed 

 meal 34 per cent. 



