BACTERIA REDUCING NITRATES AND SULFATES 187 



pinus, which reduce nitrates to gaseous nitrogen, in the presence of small 

 quantities of organic matter. In the same soil, where nitrification takes 

 place under aerobic conditions, denitrification will take place in the 

 absence of free oxygen. 



The following authentic organisms capable of reducing nitrates to 

 atmospheric nitrogen have been isolated and described (some of these 

 are probably only varieties of other species which do not denitrify) : 



Bact. denitrificans (= Bact. denitrificans I Burri and Stutzer, Pseud, stutzeri 

 Mig.) L and N (1.5 to 3 by 0.7/i), a motile, non-spore forming, aerobic organism. 



Bact. stutzeri (= Bact. denitrificans II Burri and Stutzer, Bact. nitrogenes Mig.) 

 L and N (2 to 4 by 0.7 to 0.8ju), a motile, non-spore forming, facultative anaerobic 

 organism, isolated from straw and horse manure. 48 



Bact. kunnemanni (= Bac. denitrificans III Kunnemann), a motile, non-spore 

 forming organism. 



Bact. denitrificans agilis i9 (1 to 1.5 by 0.1 to 0.3/z), a motile, peritrichic, non- 

 spore forming organism; gram-negative, facultative anaerobic, granulated and 

 developing slow; according to Lohnis this is a denitrifying variety of Bact. radio- 

 bacier. 



Bact. ulpiani (= Bac. denitrificans VI Ampola et Ulpiani), a motile, non-spore 

 forming, gram-negative organism. 



Vibrio denitrificans** (2 to 4 by 0.5^), a motile, non-spore forming organism. 



Bac. schirokikhi, &1 a motile, spore-forming, proteolytic, aerobic organism. 



Bact. praepollens,™ a small, non-motile, obligate aerobic organism, reducing 

 only nitrites. 



Bac. nitroxus b3 (No. 62, PI. X) comprising bacilli of variable dimensions, 

 globous, pyriform, filiform; they take the form of Clostridia at the time of spore 

 formation, giving an intense glycogen reaction; facultative anaerobic; on 

 repeated transfer under aerobic conditions may lose faculty of reproduction; 

 gelatin is liquefied. 



In addition to these and the above mentioned bacteria, we may also call 

 attention to a few other denitrifying forms which were isolated, such as Bact. ful- 

 vum, bi Bact. hartlebii, hh Bact. centropunctatum, Bact. nitrovorum, B. porticensis, etc. 

 Most of these organisms are strict aerobes, some being capable of decomposing 

 proteins actively. Most of them grow on nitrate (0.2 to 1.0 per cent) media, with 



48 Kunnemann, O. tJber denitrifizierende Mikroorganismen. Landw. Ver- 

 suchsta. 50: 65-113. 1898. 



49 Ampola and Garino, 1896-1897 (p. 186); Kuntze, VV. Beitriige zur Mor- 

 phologie und Physiologie der Bakterien. Centrbl. Bakt. II, 13: 1-12. 1904. 



"Sewerin, 1897 (p. 186). 

 61 Jensen, 1898 (p. 180). 

 62 Maassen, 1899 (p. 181). 

 63 Beijerinck and Minkman, 1910 (p. 546). 



54 Bierema, S. Die Assimilation von Amnion-, Nitrat- und Amidstickstoff 

 durch Mikroorganismen. Centrbl. Bakt. II, 23: 672-726. 1909. 

 66 Jensen, 1898 (p. 180). 



