OXIDATION OF SULFUR IN THE SOIL 245 



Hydrogen sulfide and sulfides are not utilized at all, which 

 sharply differentiates our organism from those of Nathanson 

 (1903), Beijerinck (1904), and Jacobsen (1914), as will be pointed 

 out later. 



Mineral requirements. Mere traces of K, Mg, Ca, Fe, in ad- 

 dition to phosphates, are sufficient for the growth of the organism. 

 As a matter of fact, good growth and good sulfur oxidation were 

 obtained by omitting, in various batches of media, each of the 

 first four minerals, but, of course, no precaution was taken to 

 eliminate any traces present in the distilled water or any sub- 

 stances that might have been dissolved out by the action of the 

 sulfuric acid on the glass of the flask. 



Source of nitrogen. Due to the very small amount of growth 

 made by the organism, the amount of nitrogen required is very 

 small: without introducing any nitrogen source into the medium, 

 some growth is obtained, the nitrogen being derived either from 

 the contamination of the other salts, the distilled water, or traces 

 of ammonia in the atmosphere. The best sources of nitrogen are 

 ammonium salts of inorganic acids (particularly sulfate), followed 

 by the ammonium salts of organic acids, after which come the 

 nitrates, asparagin and amino acids. Nitrites, in concentrations 

 used (2 grams per liter) are toxic. Good growth is obtained 

 with pepton, but the amount of sulfur oxidized is less than with 

 the other sources of nitrogen. 



Relation to oxygen. The organism is strictly aerobic, in view 

 of the fact that it derives the oxygen necessary for the oxida- 

 tion of sulfur to sulfuric acid from the atmosphere. 



Influence of organic substances. As pointed out above, glucose 

 does not act injuriously, neither do other organic substances, 

 like pepton. Substances like glycerol, alcohol, mannitol and 

 glucose seem to have a slight favorable effect in the presence of 

 a good nitrogen source. All these substances either act like 

 stimulants or else take part in the structural requirements of 

 the organism. 



Influent of stimulants. In addition to the pure organic 

 substances, above mentioned, which may stimulate to some 

 extent the growth of the organism, other substances may exert 



JOUBNAL or BACTBBIOLOOT, VOL. Til, NO. 2 



