ROBERT L. STARKE Y 327 



will not develop upon organic materials. It oxidizes sulphur, thiosulphate, and other 

 compounds of sulphur to sulphate, obtaining oxygen from nitrates by such a reaction 

 as the following: 



IX. 5Na.S A+8KN03+NaHC03 = 6Na.S04+4K.S04+4N.+ 2C0.+H,0 



AF298 = — 893 ,000 calories 



The organism has been found widely distributed in waters and soils. The results of 

 Lieske indicate that the reaction does not proceed directly to sulphate since other 

 sulphur compounds were present in the media at certain stages of growth. However, 

 none of these intermediary products accumulated. It is likely that in the oxidation of 

 sulphur or sulphur compounds by other sulphur bacteria the process is not as simple 

 as is generally assumed. 



An organism obtained by Trautwein' showed characteristics similar to Th. 

 denitrificans but differed in that it could exist either aerobically or anaerobically and 

 either as an autotroph or heterotroph. In the presence of nitrate it developed as an 

 anaerobe, and in the absence of organic compounds could obtain energy from the 

 oxidation of sulphide, sulphur or thiosulphate, but the last was the best source of 

 energy. Like the other forms, it has been found in soils, sewage, and fresh water. 



Autotrophic bacteria were first recognized by Winogradsky' in his studies of the 

 more complex sulphur bacteria, some of which are pigmented. These forms are char- 

 acterized by intracellular globules of amorphous sulphur. They develop as obligate 

 autotrophs and utilize hydrogen sulphide as a source of energy which is oxidized in at 

 least two separate stages, first to sulphur and then to sulphate. The reactions may 

 be represented as follows:-' 



X. H.S (aq.)+^0. = H.04-S 



AF2y8= —41,500 calories 



XI. S+i^O^+H.O^H.SO^ 



AF298= — 118,500 calories 



In the presence of a continuous supply of sulphide the organisms always contain 

 globules of sulphur. However, if the sulphide is all removed, the globules of sulphur 

 are oxidized to sulphate and disappear from the cells which then die. The oxidation 

 of both the sulphide and sulphur proceeds simultaneously in the presence of sulphide. 

 For the colorless organisms free oxygen and carbon dioxide are indispensable. ^ 



These higher sulphur bacteria have been found extensively in both fresh and salt 

 waters but not in soils. The pigmented forms frequently develop to such an extent 

 as to lend very striking red colors to the waters. 



Two different pigments have been obtained from the bacteriopurpurin of the purple 

 (red) sulphur bacteria.^ One, a green pigment unlike chlorophyll, is called "bacterochlorin" ; 



' Trautwein, K.: Cenlralbl.f. Bakkriol., Abt. II, 53, 513-48. 1921; 61, 1-5. 1924; see also Klein, 

 G., and Limberger, A.: Biochem. Ztsclir., 340, 473-83. 1923. 



^ Loc. cit. 



3 See, however, Baas-Becking, L. G. M.: Ann. Hot., 39, 613-50. 1925. 



1 Keil, P.: Beitr. z. Biol. d. Pflanzen, ii, 335-72. 1912. 



s Molisch, H.: Die Piirpurbaclerien nach ncite Untcrsiichungen. 95 pp. Jena: Gustav Fischer, 

 1907; Buder, J.: Jalir.f. Wiss. Botan., 58, 525-628. 1919. 



