AUTOTROPHIC BACTERIA 93 



I. Thread-forming bacteria consisting of sheaths with included cells generally 

 plainly visible. Reproduction by internally produced conidia or by the separa- 

 tion of motile and non-motile cells (Trichohacteria). 



Crenothrix 

 Leptothrix 

 L. ochracea 

 L. Irichogenes 



II. True bacteria: 



Gallionella (^Spirophyllum) 



Siderocapsa 



Sideromonas 



Only a few of the numerous forms described are true iron bacteria. 



It was assumed that the higher bacteria present a variety of forms, 

 such as single threads composed of cylindrical cells placed end to end 

 and generally inclosed in sheaths; ribbon forms, twisted spirally; 

 cylindrical threads showing false branching, or coiled threads and 

 ribbon forms produced by the bending of the filaments in the middle 

 and the twisting of the ends around each other like a rope. 79 Gallio- 

 nella (Spirophyllum) 80 was considered to be the most abundant of the 

 iron bacteria. The flat ribbon-like or tape-like threads are twisted in 

 the form of spirals. These spiral bands may occur as single filaments or 

 may be coiled together. 



Some of the iron bacteria are also capable of oxidizing manganese 

 salts and precipitate manganese hydrates in their cells; 81 Winogradsky 

 suggested that we may be dealing here with organisms less specialized 

 than the other autotrophic bacteria, some being iron-bacteria in the 

 proper sense (Gallionella, Spirophyllum, etc.), some iron-manganese 

 bacteria (Crenothrix, Leptothrix, etc.) and some may possibly be 

 obligate manganese-bacteria. 



Winogradsky 82 found in 1888 that Leptothrix will live and grow only 

 in solutions in which iron is present in the ferrous form; where the living 

 cells are present, a brown coloration of the sheath takes place due to the 

 oxidation of the iron salt. The oxidation of ferrous compounds (FeC0 3 ) 



79 Harder, E. C. Iron depositing bacteria and their geologic relations. Prof, 

 paper 113, U. S. Geological Survey, Dept. of Interior, 1919. 



80 Ellis, D. On the discovery of a new genus of thread bacteria (Spirophyllmn 

 Jerrugineum Ellis). Proc. Roy. Soc. Edinburgh, 27: 21-34. 1907. Lieske, 1911 



(p. 95). 



81 Schorler, B. Beitriige zur Kenntnis der Eisenbakterien. Centrbl. Bakt. II, 

 12: 681-695. 1904; Die Rostbildung in den Wasserleitungsrohren. Ibid. 15: 

 564-568. 1906. 



82 Winogradsky, S. liber Eisenbakterien. Bot. Ztg. 46: 262-270. 1888. 



