Decomposition of Ilcmicclliiloses 115 



oped. When the leaetioii of the soil was aeicl (/;il 5.7-6.2), the 

 N'ibrios were reduced and Spirocluicta cijtophaga grew abundantly. 

 At a still greater aeidit\ , fungi were the only eellulose-d(^stroyiug 

 forms; among these Trichodcrma and VeniciUium were most active. 

 The fungi found in neutral soils included Mijcogonc nig,ra, Stachij- 

 botnjs, Coccospora agricola, and Botr{/<).s))()ritnn. 



2. The cultures of bacteria isolated from the \arious soils behaved 

 in pure culture in a manner similar to that in the natural soil. Four 

 species of Vibrio were not active upon cellulose below ;;H 6.4 but 

 gave optimum growth at pH 7.1-7.6. Spirochacta cijtophaga, how- 

 ever, was able to grow at pH 5.6-6.0. 



3. All cultures thus isolated were able to decompose not only pure 

 cellulose but also lignified cellulose of straw. 



4. The nitrogen required for cellulose decomposition varied from 

 1 part nitrogen to 25-54 parts cellulose. 



5. The cellulose-decomposing bacteria did not produce any humus- 

 like substances. The fungi Mijcogone nigra and Stachyhotrys gave 

 rise to humus. 



Dubos used a simple mineral salt solution for studying cellulose- 

 destroying aerobes. This medium consisted of 0.5 gm NaNOs, 1.0 

 gm K.HPO^, 0.5 gm MgS04-7HoO, 0.5 gm KCl, 0.01 gm FeS04- 

 7H2O, and 1,000 ml water. Strips of filter paper were placed in the 

 tubes containing this medium, and the tubes were inoculated with 

 various dilutions of soil. This method proved to be very favorable 

 for the isolation of Cytophaga and other cellulose-destroying bac- 

 teria. The medium could also be used for determination of the 

 quantitative distribution of cellulose-decomposing bacteria in soil. 



Decomposition of Hemicelluloses 



Hemicelluloses represent a great variety of chemical compounds, 

 usually divided into polysaccharides, or those compounds which give 

 on hydrolysis simple sugars (CcHioOo, C5H10O5), and polyuronides, 

 or those that gi\e on hydrolysis sugar acids (CuHioOt) or mixtures 

 of sugars and sugar acids. The designation of individual hemicellu- 

 loses is based on the sugar produced on their hydrolysis by acids or 

 enzymes. On hydrolysis, pentosan gives pentose sugar; araban yields 

 arabinose; xylan gives xylose; hexosans yield hexose sugars, galactan 

 giving galactose and mannan giving mannose. 



The polyuronides are more complex. Pectin is an abundant con- 

 stituent of fruits and vegetables and is made up of galactose, arabi- 



