AUTOTROPHIC BACTERIA 85 



became covered with free sulfur, intermixed with bacteria. On making a 

 transfer into a fresh flask with medium, a sulfur layer was obtained in 

 24 hours, originating from the thiosulfate. This reaction is exothermic 

 and functions as a source of energy. The energy is used for the reduc- 

 tion of NaHC0 3 and for the building of the bacterial body. Calcium 

 sulfide, hydrogen sulfide and tetrathionate can replace the thiosulfate. 

 The ammonium salt can be replaced by nitrates. None of the 

 organic substances tested could replace the carbonic acid as a source of 

 carbon. The organism, Thiobacillus thioparus Beijerinck, was reported 

 to be a short rod, 3 by 0.5ju, not forming any spores, very motile and 

 very sensitive, so that on plates the organisms die off in a week. 



By adding 2 per cent agar to the above medium the organism can be 

 grown on the plate; transfers are then made from individual colonies 

 into fresh lots of the liquid medium giving a pure culture of the organism. 

 The colonies are of a pin-point form and are distinguished from con- 

 taminations by their yellow appearance, due to an abundant separation 

 of sulfur. According to Duggeli, 61 this organism is only 0.3 to 0.5/x long. 

 Jacobsen 62 demonstrated that this organism can also oxidize sulfur to 

 sulfuric acid, in the following medium: 



K0HPO4 0.5 gram CaCOj or MgCO s . . . . 20.0 grams 



NELC1 ' 0.5 gram Precipitated sulfur. . . 10.0 grams 



MgCl 2 0.2 gram Distilled water 1000 cc. 



An organism similar to the Thiobacillus thioparus was found 63 to be 

 active in the oxidation of sulfur in alkali soil, giving the gross micro- 

 scopic reactions of the form studied by Nathanson and Beijerinck. 



Group IV of the sulfur bacteria includes, in addition to the aerobes, 

 anaerobic bacteria which are able to obtain their oxygen from nitrates. 

 Beijerinck obtained an oxidation of sulfur accompanied by a reduction 

 of the nitrate to atmospheric nitrogen by using the following medium 

 in closed flasks and incubating at 30°C. 



KNO3 . 0.5gram CaC0 3 20.0 grams 



Na 2 C0 3 0.2 gram Sulfur 100.0 grams 



K 2 HP0 4 0.2 gram Canal water 1000.0 cc. 



61 Duggeli, 1919 (p. 82). 



62 Jacobsen, H. C. Die Oxidation von elementarem Schwefel durch Bakterien. 

 Folia Microb. 1: 487-496. 1912; 3: 155-162. 1914. 



63 Waksman, S. A. Microorganisms concerned in the oxidation of sulfur in the 

 soil. V. Bacteria oxidizing sulfur under acid and alkaline conditions. Jour. 

 Bact. 7: 609-616. 1922. 



