328 AUTOTROPHIC BACTERIA 



the other, a red pigment of the nature of a carotin, is called "bacterioerythrin." The pig- 

 mented bacteria differ in their nutrition from the colorless forms in that they require light 

 in addition to hydrogen sulphide and carbon dioxide, but only little or no free oxygen.' Some 

 photosynthetic reaction appears to be associated with the utilization of the inorganic energy, 

 but the action may be explained in at least two ways. Bavendamm^ expressed the opinion 

 that the organism used two reactions as sources of energy, both a photosynthetic one and 

 the oxidation of the sulphide. Since the cells failed to develop in the absence of either light 

 or hydrogen sulphide, but could exist in the absence of oxygen, it seems more likely that the 

 two processes are more closely related. It may be that the light serves as an agent to reduce 

 carbon dioxide to at least intermediary synthetic substances and furnishes oxygen for the 

 oxidation of the sulphide. This reaction is used as a further source of energy for metabolic 

 processes. The following reaction was suggested by Baas-Becking and Parks :3 



XII. 6CO.+ i2H.S = C6H„06-F6H.O+i2S 



AF298 = + 2 1 2,000 calories 



Under these conditions the deficiency of energy is supplied by the photosynthetic reaction. 

 BACTERIA WHICH OXIDIZE FERROUS OR MANGANOUS COMPOUNDS 



Precipitation of large amounts of ferric hydrate has been repeatedly observed from 

 many natural waters such as mineral springs, mines, and flows from other subter- 

 ranean streams. Associated with such deposits there generally occur cells of fila- 

 mentous and other bacteria which are incased in sheaths of ferric hydrate. Some are 

 multicellular organisms and others small spherical, oval, or bent cells incased in ir- 

 regular masses of ferric hydrate or carrying ribbon-like streamers of the substance 

 attached to the cells. In many cases these incrustations have been considered to be 

 sufficient evidence to indicate that these organisms are autotrophic. Pure culture 

 studies'" have shown that some of them are obligate autotrophs {Leptothrix ochraceae, 

 L. trichogenes, Gallionella fcrruginca, G. minor) and others facultative {Leptothrix 

 crassa, Crenothrix polys pora). Manganese compounds may be substituted for ferrous 

 compounds with some of these bacteria. The reaction by which they may obtain 

 energy may be represented as follows: 



XIII. 4FeC03+0.+6H.O = 4Fe(OH)3-F4CO. 



AF298 = — 8 1 ,000 (approximate) 



Since chemical oxidation of ferric hydrate may be so common in natural waters, 

 the relative importance of the iron bacteria as factors in iron deposition is not known. ■'^ 



' Engelmann, T. W.: Pfliigcrs Arch. f. d. gcs. Physiol., 30, 95-124. 1SS3; 42, 183-86. 1888; 

 Botan. Zeit., 46, 66 r. 1888. 



' Loc. cit. 3 Loc. cil. 



^ Winogradsky, S.: Bolan. Zcil., 46, 261-70. 1888; Centralhl.f. BaktcrioL, Abt. II, 57, 1-21. 1922; 

 Lieske,R.: Jahr.f. Wiss. Botan., 4g,gi~i2j. zgii;Cenlra!bl.f. BaklcrioL, .\hl. II, 49, 4.1:^-2$. 1919; 

 Molisch, H.: Die Eisenbakterien. 83 pp. Jena: Gustav Fischer, 1910; Cholodii}^, N.: Die Eiscn- 

 baktericti. 162 pp. Jena: Gustav Fischer, 1926. 



5 Harder, E. C: U.S. Gcol Survey, Prof. Paper i ij. 89 pp. 1919; Gruner, J. W.: Econ.Gcol., 17, 

 407-60. 1922; Halvorson, H. O., and Starkey, K. L.: /. Pliys. Chew., 31, 626-31. 1927; Starkey, 

 R. L., and Halvorson, H. O.: Soil Sci., 24, 381-402. 1927. 



