282 SYNTHETIC CULTURE MEDIA 



larly, the essentials for the growth of Nitrobacter (oxidizing nitrites to nitrates) are a 

 suitable salt of nitrous acid (usually potassium nitrite), carbon dioxide or carbonates, 

 and a satisfactory buffer. 



Numerous synthetic media have been developed for the group of organisms ca- 

 pable of securing "growth energy" for the assimilation of carbon dioxide by the oxida- 

 tion of sulphur or its compounds. Those organisms which have been cultured belong 

 to the genus Thiobacillus of Beijerinck. One species, Thiobacillus denitrificans Bei- 

 jerinck,' secures its "growth energy" for the assimilation of carbon dioxide under 

 anaerobic conditions by the simultaneous reduction of nitrates to free nitrogen and the 

 oxidation of elementary sulphur to sulphuric acid. Essential to such a medium are 

 therefore sulphur (elementary), nitrates, carbonates (or carbon dioxide), and a 

 suitable buffer. , 



Other species of the genus Thiobacillus oxidize sulphur or its compounds under 

 aerobic conditions, and a variety of synthetic media have been devised for their study. 

 These contain either elementary sulphur or reduced sulphur in the form of thio- 

 sulphates. Carbon is derived from carbon dioxide or the carbonates, and nitrogen 

 usually from ammonia. 



Synthetic media for the growth of certain of the autotrophic iron bacteria 

 (Chlamydobacteriales) have been developed by Migula^ and Schorler.^ Apparently in 

 all cases there must be provided a soluble salt of ferrous iron or manganous man- 

 ganese, carbon dioxide or carbonates, ammonia, and oxygen. It is claimed that 

 "growth energy" is secured by the oxidation of the metallic ion. 



Certain bacteria (as members of the genus Hydrogenomonas) develop in a 

 synthetic culture medium supplied with gaseous hydrogen, oxygen, carbon dioxide, 

 and a suitable source of nitrogen (as ammonia)."* 



Other organisms have been described which develop on a similar culture medium 

 in which the hydrogen is replaced by carbon monoxide as does Carboxydonionas 

 oligocarbophila described by Beijerinck and Van Delden,^ or by methane {Methano- 

 monas methanica) J' 



Non-autotrophic (better, non-oligocarbophilous) organisms require for their 

 growth the presence of organic (carbon) compounds. Apparently in all cases studied 

 these carbon compounds serve at least three functions: (o) they may be oxidized in 

 whole or in part with the freeing of energy of use to the cell, {h) they may be used in 

 the synthesis of protoplasm or essential cell parts, or (c) they may be stored (after 

 more or less modification) as reserve food. Carbon compounds which have been used 

 in the preparation of synthetic media are very numerous. Such synthetic media may 

 conveniently be classified on the basis of the source of the nitrogen supplied. 



The nitrogen-fLxing bacteria are frequently cultured on synthetic media; in most 

 cases the "energy source" supplied is a carbohydrate or a polyatomic alcohol. The 



' Beijerinck, M. W.: Centralbl.f. Bakteriol., II Abt., ii, 587. 1904. 



' Migula, M.: Arbeiten aus den bakt. Inst, dcr techn. Hochschide zu Karlsruhe, i, 235, 238. 1S94. 



3 Schorler, B.: Centralbl.f. Bakteriol., II Abt., 12, 691. 1904. 



4 Kaserer, H.: ibid., 16, 681-96. 1906. 



s Beijerinck, M. W., and Van Delden, A.: ibid., 10, 33-47. 1903. 

 ' Sohngen, N. L.: ibid., 15, 513-17. 1906. 



