188 PRINCIPLES OF SOIL MICROBIOLOGY 



the formation of a gas (largely N, some C0 2 ) and nitrite. In the absence of free 

 oxygen, these organisms can exist anaerobically in the presence of nitrate. 



A thermophilic denitrifying bacillus (3.5 to 7 by 1 to 1.8/x), facultative 

 anaerobic, reducing nitrates with the formation of gas and growing at 

 high temperatures (52°C.) has also been described. 56 



Several organisms reducing nitrates are capable of obtaining their 

 energy from inorganic compounds. Thiob. denitrificans Beij. oxidizes 

 sulfur and reduces nitrates to nitrogen gas. This organism, or rather 

 group of organisms, is widely distributed in the soil. 57 - 58 Thiosulfate 

 can be oxidized by the organism under anaerobic conditions only in 

 the presence of nitrate as a source of oxygen. 59 The utilization of the 

 energy obtained by the oxidation of hydrogen gas for the reduction of 

 nitrates has been pointed out by Niklewski 60 for H. agilis. 



The decomposition of cellulose in the soil may be carried on by the 

 symbiotic action of two bacteria, one reducing nitrate to atmospheric 

 nitrogen and the other decomposing the cellulose; the decomposition 

 products of the cellulose are used by the nitrate reducing organism as a 

 source of energy, which enables it to reduce the nitrate, while the oxygen 

 thus liberted is utilized by the cellulose decomposing organism, under 

 anaerobic conditions. 61 



Bacteria reducing sulfates to H2S. A detailed study of the formation 

 of hydrogen sulfide in nature is given elsewhere (p. 600). It is sufficient 

 to call attention here to the bacteria capable of producing this sub- 

 stance as a result of reduction of sulfates and other oxygen-rich sulfur 

 compounds (like thiosulf ates) . Microspira desulfuricans (No. 63, PI. 

 X), capable of bringing about this reduction, was first studied by 

 Beijerinck, 62 then obtained in pure culture by Van Delden. 63 It was 

 isolated on the following medium: 



K2HPO4 0.5gram MgS0 4 or CaS0 4 1.0 gram 



Sodium lactate 5.0 grams FeSC>4 Trace 



Asparagine 1.0 gram Tap water 1000 cc. 



88 Ambroz, 1913 (p. 158). 

 57 Lieske, 1912 (p. 86). 

 68 Gehring, 1914 (p. 87). 

 69 Trautwein, 1921 (p. 87). 



60 Niklewski, 1914 (p. 99). 



61 Gerretsen, 1921 (p. 736). 



62 Beijerinck, M. W. tlber Spirillum desulfuricans als Ursache von Sulfatre- 

 duktion. Centrbl. Bakt. II, 1: 1-9, 48-59, 104-114. 1895. 



63 Van Delden, A. Beitrag zur Kenntnis der Sulfatreduktion durch Bak- 

 terien. Centrbl. Bakt. II, 11: 81-94, 113-118. 1904. 



