REDUCTION PROCESSES IN THE SOIL 



547 



utilized for the synthesis of the microbial protoplasm. The soil was 

 believed to act as a catalyzer which hastens the process since, on con- 

 secutive transfer, the activities of the organism are weakened. 



According to Beijerinck 19 the organisms concerned in the process may 

 occur in two physiologically different modifications, which are heredi- 

 tarily constant when the feeding conditions remain unchanged. One, 

 an autotrophic form which is adapted to inorganic media (sulfur- or 

 thiosulfate-carbonate-nitrate) and which shows chemosynthesis; the 

 other, an heterotrophic form, requires organic food. The heterotrophic 

 forms preserve the power of denitrification with organic food. 



Trautwein 20 also demonstrated that some soil organisms are capable 

 of oxidizing thiosulfate under aerobic conditions in the absence of nitrate; 



TABLE 53 



Influence of nitrate upon the decomposition of sucrose in (4 per cent) nutrient 



bouillon, under anaerobic conditions 23 



Volume of gas produced 



C0 2 per 100 of gas 



H 2 per 100 



NO per 100 



N 2 per 100 



N 2 per 100 



BACT. LACTIS AEROGENES 



Nitrate 

 present 



628.4 



57.6 







6.7 



2.3 



23.4 



Nitrate absent 



1715.15 

 64.7 

 33.4 











PNEUMOBACILLUS OP 

 FHIEDLANDER 



Nitrate 

 present 



548.9 

 69.3 







1.2 





 29.5 



Nitrate absent 



1118.9 



62.9 



35.0 











growth and autotrophic respiration took place anaerobically only when 

 nitrate was present as a source of oxygen. 



Nitrate reduction can be brought about readily by a number of soil 

 bacteria, under anaerobic conditions, when carbon sources are available 

 as source of energy. 21 Nitrates enable many facultative anaerobes to 

 develop under anaerobic conditions, using sources of carbon which 

 could otherwise not be utilized. 22 



19 Beijerinck, M. W. Chemosynthesis at denitrification with sulfur as source 

 of energy. K. Acad. Wetenschappen. Amsterdam, 22: Nos. 9 and 10. 1920. 



20 Trautwein, 1924 (p. 88). 



21 Van Iterson, G. Anhiiufungsversuche mit denitrifizierenden Bakterien. 

 Centrbl. Bakt. II, 12: 106-115. 1904. 



22 Ritter, G. Beitrage zur Physiologie der fakultativ anaeroben Bakterien. 

 Centrbl. Bakt. II, 20: 21-38. 1908. 



