AUTOTROPHIC BACTERIA 101 



dize hydrogen by using the oxygen obtained from the reduction of nitrates and 

 sulfates and in some cases of citrate, tartrate and oxalate. The presence of 

 nitrate enables the organism to oxidize hydrogen anaerobically. The organism 

 can also exist aerobically using free oxygen for the autotrophic oxidation of 

 hydrogen. It can also exist heterotrophically similar to the other organisms. 



For the isolation of pure cultures of hydrogen oxidizing bacteria, Lebedeff 110 

 used a medium consisting of 1000 parts of water, 2.0 KN0 3 , 0.5 NaH 2 P0 4 , 0.2 

 MgS0 4 , traces of FeCl 3 and an atmosphere of hydrogen containing 5 to 15 per 

 cent C0 2 . One hundred cubic centimeter portions of medium were placed in 

 side-arm flasks, inoculated with soil; after evacuating and introducing the gas, 

 the flasks were sealed. After 5 to 6 days of growth the organism appeared in the 

 form of a surface pellicle. After 3 to 4 transfers, the organism was isolated on a 

 silica gel plate, kept in an atmosphere of hydrogen containing 5 to 10 per cent 

 C0 2 . After 8 to 10 days, milky-white regular colonies appeared on the plate. 

 These consisted of rod-shaped (spore forming ?) bacteria, 1.2 to 1.5ju long, motile 

 by means of a single flagellum. The organism was heterotrophic, forming on 

 gelatin milky-white colonies which changed later to brownish, and was named 

 Bac. hydrogenes. Gelatin was liquefied, various sugars, organic acids and pro- 

 tein derivatives were utilized as sources of carbon. Optimum temperature 26°C. 



Recent studies 111 ■ 112 have shown that a number of different species of 

 hydrogen bacteria are present in the soil. They live autotrophically 

 with hydrogen as a source of energy and heterotrophically in the 

 absence of hydrogen, thus being facultative autotrophic. The different 

 species differ in their sensitiveness to oxygen pressure or in the ability 

 to use combined oxygen for the oxidation of hydrogen. A newly found 

 species Bacillus yycnoticus was studied in detail. It is a rod-shaped 

 organism, 1.5 to 4 by 1.0/*, every preparation containing non-motile 

 and motile cells, with peritrichic flagellation. In addition to the rods, 

 true cocci as well as giant cells and thick-walled, egg-shaped cells, ten 

 times as large as the normal bacterial cell, were found in the culture. 

 The purity of the culture was established by single-cell isolation, using 

 Bum's India ink method. The giant cells are involution forms, pro- 

 duced under special environmental conditions. The spores swell up in 

 length and width, before they can germinate, and may account for the 

 egg-shaped figures; they also break up into true cocci. 



The organism is grown in an inorganic solution containing sufficient 



110 Lebedeff, A. F. Investigations of the chemosynthesis of Bacillus hydro- 

 genes (Russian). Odessa. 1910. 



111 Grohmann, G. Zur Kenntnis Wasserstoff-oxydierender Bakterien. Centrbl. 

 Rakt. II, 61: 256-271. 1924. 



112 Ruhland, W. Beitriige zur Physiologie der Knallgasbakterien. Jahrb. 

 Wiss. Bot. 63: 321-389. 1924. 



