84 PRINCIPLES OF SOIL MICROBIOLOGY 



required for nutrition. These results are in direct opposition to the 

 earlier ideas of Winogradsky and others. 



Group IV. This group includes the colorless organisms that do not 

 accumulate sulfur within their cells, but produce sulfur abundantly from 

 thiosulfate and hydrogen sulfide outside of their cells (No. 21, PI. IV). 

 These were first demonstrated by Nathanson 59 (1902) in sea water. 

 They were found to be able, by means of oxidation of hydrogen sulfide 

 or sodium thiosulfate, to reduce carbonic acid and construct organic sub- 

 stances from it. Nathanson used a medium of the following composi- 

 tion: 



Na 2 S 2 3 2-10 grams NaCl 30.0 grams 



KN0 3 1 gram MgC0 3 some 



Na 2 HP0 4 0.5 gram Water 1000 cc. 



MgCl 2 2.5 grams 



A good growth of these bacteria was obtained after 1 to 2 days, in the 

 form of a white pellicle covering the surface; this consisted of rod- 

 shaped organisms intermixed with amorphous sulfur. 



On adding agar to the above medium Nathanson has been able to 

 isolate the organism in pure culture. In the absence of the carbonate, 

 but in the presence of air containing carbon dioxide, the growth was 

 much slower. In the absence of both carbonate and carbon dioxide, 

 no growth took place, even in the presence of various organic substances. 

 The medium did not become acid even in the absence of carbonate. 

 While no sulfur accumulated within the cell, there was an abundant 

 production of free sulfur outside of the cell, not in direct contact with 

 the colony but at some distance from it. This led to the theory of 

 extracellular oxidation. Nathanson suggested that the sulfur is pro- 

 duced in a secondary reaction between the undecomposed thiosulfate 

 and the tetrathionate formed from the oxidation of the thiosulfate. 



Beijerinck 60 employed the following medium: 



Na 2 S 2 3 -5H 2 5.0 grams NH 4 C1 0.1 gram 



NaHC0 3 l.Ogram MgCl 2 O.lgram 



Na 2 HPO < 0.2 gram Water 1000 cc. 



The medium was left unsterilized and was inoculated with canal water 

 and incubated at 28°to 30°C. In 2 to 3 days, the surface of the medium 



69 Nathanson, A. tJber eine neue Gruppe von farblosen Schwefelbakterien 

 und ihren Stoffwechsel. Mitt. Zool. Station, Neapel 15: 655. 1902. 



60 Beijerinck, M. W. Uber die Bakterien, welche sich im Dunkeln mit Kohlen- 

 saure als Kohlenstoffquelle ernahren konnen. Centrbl. Bakt. II, 11: 593-599. 

 1904. 



