ROBERT L. STARKEY 325 



aerobic process requiring abundance of free oxygen and carbon dioxide.' The limiting 

 reactions for the process are close to neutrality' (in solution cultures pH 7.4—8.4 for 

 Nitrosomonas and pH 6.5—10.3 for Nitrobacter. Much wider ranges of activity are 

 observed in natural habitats.) Their discovery and isolation by Winogradsky was the 

 climax to a long series of investigations aiming to explain the mechanism of nitrate 

 formation in soils. 



BACTERIA WHICH OXIDIZE SULPHUR OR COMPOUNDS OF SULPHUR 



The organisms concerned in these transformations represent a variety of forms 

 concerned in many different types of reactions, some of which appear to be among the 

 most unique physiological processes for deriving functional energy. They are of con- 

 siderable importance in the oxidation of natural sulphides in waters, and may be 

 active agencies in the transformation of inorganic sulphur compounds originating 

 from organic combinations in decomposition processes.'' 



The known organisms included as the "simple sulphur bacteria" are all non- 

 sporulating small rods. Some are obligate autotrophs and others facultative; some 

 are aerobic, some facultative, and others obligate anaerobes. Among the aerobic 

 forms are two very distinct organisms, both obligate autotrophs, one of which de- 

 velops at reactions close to neutrality and the other under very acid conditions. 



The first — Thiobacillus thiopariis Beijerinck^ — occurs very , widely in soils and 

 natural bodies of water. It oxidizes thiosulphate (NajSiOj), tetrathionate (Na2S406), 

 sulphur, and sulphide. Some of the reactions may be explained as follows: 



V. 3Na.S203+50. = 2Na.S04+Na3SA 



AF298= — 260,000 calories (approximate) 



VI. S+i|0.+H.0 = H.S04 



A F298 = — 1 1 8, 500 calories 



As a result of the growth of this organism, precipitated sulphur is formed outside 

 of the cells. It is generally believed that this arises as a product of the fundamental 

 reaction such as expressed by Beijerinck: 



VII. 2Na.SA+02 = 2Na.S04+2S 



'Winogradsky, S., and Omeliansky, W.: Cenlralbl. f. BaktcrioL, Abt. II, s, 329-43, 377-87, 

 429-40. 1899; Godlewsky, E.: ibid., 2, 458-62. 1896; Meyerhof, O.: Archiv.f. d. ges. Physiol., 164, 

 353-427; 165, 229-84. 1916; 166, 240-80; 1917. Bonazzi, A.: /. Bact., 6, 479-99. 1921; 8, 343-63. 

 1923; Gibbs, W. M.: Soil Sci., 8, 427-81. 1919. 



^ Gaarder, T., and Hagem, O.: Bergens Mus. Aarhok, No. 6, i-^i. 1920. See also Meyerhof, O.: 

 loc. ciL; Meek, C. S., and Lipman, C. B.: /. General Physiol., 5, 195-204. 1922. 



3 Diiggeli, M.: Neiij. d. Naturfors. Gescll. Zurich, No. 121. 43 pp. 1919; Bavendamm, W.; Die 

 farblosen und rotcn Schwefelbakterien. 156 pp. Jena: Gustav Fischer, 1924; Waksman, S. A., J. Bad., 

 7, 231-56. 1922; Baas-Becking, L. G. M.: Ann. Bol., 39, 613-50. 1925. 



* Nathansohn, A.: Mitt. a. d. zoolog. Slation Neapel, 15, 655. 1902 {Cenlralbl. f. Bakleriol., Abt. 

 II, II, 109. 1904); Beijerinck, M. W.: Arch. d. Sci. Exacles Nat. Haarlem (2d ser.), 9, 131-57; 

 Cenlralbl. f. Bakleriol., Abt. II, 11, 592-99. 1904; Jacobsen, H. C: Folia MikrobioL, i, 487-96. 

 1912; 3, 155-62. 1914; Waksman, S. A.: 5oi7 5'«., 13, 329-35. 1922; /. .4 gr. i?e^., 24, 297-305. 1923; 

 Kilpatrick, M., Jr., and M. L.: J. Am. Ghent. Soc, 45, 2132-35. 1923. 



