324 AUTOTROPHIC BACTERIA 



2. Facultative autotrophic 



(a) Facultative anaerobic (species of Trautwein) 

 b) Higher bacteria (complex in morphology) 



1. Colorless (includes the genera Beggiatoa, Thiothrix, Thioploca, Achromatium, 

 Thiophysa, Thiovulum, and Thiospira) 



2. Pigmented-red or purple bacteria (includes the genera Thiocystis, Thiocapsa, 

 Thiosarcina, Lamprocystis, Thiopedia, Amocbohader , Thiothece, Thiodictyon, Thio- 

 polycoccus, Chromatium, Rhabdochromatium, Thiospirillum, Rhodocapsa, Rhodo- 

 thece) 



C. Bacteria which oxidize ferrous or manganous compounds 



a) Simple bacteria 



1. Long excretion filaments (genus Gallionella) 



2. Coccoid or oval shapes in masses (genera Siderocapsa and Sideromonas) 



b) Filamentous bacteria (genera Leptothrix and Crenothrix) 



D. Bacteria which oxidize hydrogen 



Winogradsky was the first to recognize the existence of bacteria with autotrophic 

 habits. The first to be studied were certain of the higher sulphur bacteria' and later 

 iron bacteria^ and nitrifying organisms.^ 



BACTERIA WHICH OXIDIZE COMPOUNDS OF NITROGEN 



Two distinct reactions are performed by organisms of this group: (i) oxidation 

 of ammonia to nitrite {N itrosomonas and Nitrosococcus) and (2) oxidation of nitrite 

 to nitrate {N itrobacter) , The transformation proceeds according to the following 

 reactions: 



III. NH4++i|0. = NO.-+H.O+2H+ (10-8) 



AF298= —66,500 calories 



IV. N0.-+§0. = N03- 



AF298= 17,500 calories 



These reactions are produced by different bacteria, and no single species is known 

 which can oxidize ammonia completely to nitrate.'' These organisms, called "nitri- 

 fiers," are strict autotrophs and are unable to exist in the absence of their specific 

 sources of energy: ammonia for the nitrite formers and nitrite for those which oxidize 

 nitrite to nitrate. The organisms are non-sporulating cocci or short rods. They are 

 very widely distributed in nature, occurring in practically all arable soils and in many 

 bodies of water. These organisms are of particular importance in their natural habitat 

 since they appear to be the agents primarily responsible for the formation of nitrate 

 which is so generally utilized by higher plants as the source of nitrogen. It is an 



•Winogradsky, S.: Botan. Zeit., 45, 489-507, 513-23. 529^39, 545-^59. 569-76, 585^94, 606-10. 

 1S87; Bcilrdgc ziir M or phol ogie mid Physiologic der Balder icn. Ziir Morphologic und Physiologic dcr 

 Schwefelbakkricn. 120 pp. Leipzig: Felix, 1888. 



» Winogradsky, S.: Bolan. Zeit., 46, 261-70. 188S. 



3 Winogradsky, S.: Ann. del'Inst. Pasteur, 4, 213-31, 257-75, 760-71. 1890. 



"t See, however, Kaserer, IL: Zlschr. f. d. landiv. Versuch. in Oesler, lo, 37. 1907 (Centralhl. f. 

 Bakieriol., Abt. II, 20, 170. 190S); Sach, J.: ibid., 62, 15-24. 1924. 



