THE TH IONIC ACID BACTERIA 223 



These are regarded as related to, but not identical with, 

 Thiohacillus ihioparus. Another is that isolated by Waksman 

 and Joffe and named Thiohacillus thiooxidans. This organ- 

 ism has the following characters : It is rod-shaped and very 

 small, being less than i^ long and about 0-5/x in thickness, non- 

 motile, Gram positive, aerobic. It grows readily on solid media, 

 and oxidizes sulphur to sulphates. Carbon is obtained from 

 the CO2 of the atmosphere, whilst nitrogen is best supplied by 

 ammonium compounds. Growth is stimulated by the addition 

 of such organic compounds as glycerol, alcohol, mannitol, and 

 glucose, and certain inorganic compounds like thallium nitrate, 

 aluminium sulphate and manganese sulphate. The optimum 

 temperature is 28°-30°C. The culture medium is acidified 

 by its development, and the amount of thiosulphate increases 

 steadily with the growth of this species. It is stated that this 

 organism does not cease its development until the acidity 

 reaches the low value of pYi 0-6 — ro. This is probably the 

 most acid condition under which any microorganism has been 

 known to exist. 



H. D. Brown has obtained from sewage and activated 

 sludge an organism which appears to be identical with Thio- 

 bacillus thiooxidans, and Waksman has recommended a med- 

 ium in which its cultivation may be best secured: — 



The physiology of this organism has been investigated by 

 Starkey, who finds that a parallel may be drawn between the 

 rapidity of growth and the extent to which sulphur oxidation 

 has been accomplished. He therefore argues that the oxi- 

 dation of sulphur is an essential process in the metabolism 

 of Thiohacillus thiooxidans. Starkey also found that whilst 



