326 AUTOTROPHIC BACTERIA 



Since the sulphur is precipitated outside of the cells it seems likely that it is produced 

 by some secondary reactions independent of the vital reactions of the cells. 



The bacterium developing under acid conditions — Thiobacilliis thiooxidans Waks- 

 man and Joffe' — is distinctive in that it is able not only to tolerate but to produce 

 higher concentrations of acid (also H+) than any other living organism yet known.^ 

 Further, this acid is mineral and not organic. Its growth is inhibited in alkaline solu- 

 tions but may not be injuriously affected in soils at neutral or alkaline reactions. 

 In solutions, growth is most rapid at the very acid range of pH 2.0-3.0. It may fur- 

 ther produce from 5 to 10 per cent (2N) sulphuric acid from the oxidation of elemen- 

 tary sulphur. It oxidizes sulphur and thiosulphate to sulphate quantitatively with 

 the accumulation of no intermediary products in purely inorganic media. The oxida- 

 tion of sulphur may be explained by reaction VI, but the thiosulphate oxidation may 

 occur as follows: 



VIII. Na.SA+H.O+20. = Na.S04+H.S04 



This reaction was also suggested by Nathansohn for Th. thioparus, but since the 

 medium did not become acid, he believed that reaction V better explained the process. 

 With thiosulphate as the source of energy for Th. thiooxidans, some sulphur may be- 

 come precipitated as the oxidation proceeds but this is further oxidized to sulphate. 

 This sulphur probably originates from some secondary reactions of the sulphuric acid 

 with the thiosulphate. 



Th. thiooxidans was obtained from composts of sulphur, soil, rock phosphate, 

 and was probably introduced with the sulphur. It has been noted in soils about 

 sulphur mines but has not been found generally in soils which have not received 

 applications of sulphur.^ Its distribution and importance under natural conditions is 

 but little known. It is an obligate autotroph and fails to develop in the absence of 

 its specific energy source in the form of sulphur or incompletely oxidized compounds 

 of sulphur. 



Another of the morphologically simple sulphur bacteria is an anaerobic form — 

 Thiobacillus denitrificans Beijerinck.^ It grows only in the absence of free oxygen and 



' Waksman, S. A., and Joffe, J. S.: Science (N.S.), 53, 216. 192 1; Proc. Soc. Ex per. Biol, b' Med., 

 18,1-3. 1921; /. £/o/. CAem., 50, 35-45. 1922; /. 5ac/., 7, 239-56. 1922; Waksman, S. A.: Soil Sci., 

 329-36. ig22; J. Bact., 7, 602-16. 1922; Waksman, S. A., and R. L. Starkey: Proc. Soc. Exper. Biol. 

 &" Med., 20, 9-14. 1922; J. General Physiol., 5, 285-310. 1923; Starkey, R. L.: /. Bad., 10, 135-63, 

 165-95. 1925. 



' Of interest may be the early observation of Preyer: Silzmii^ab. Bcr. Med. Gcs. Natiir. Hcilkiinde 

 in Bonn, pp. 6-9. i866 (Bayliss, J. M.: Principles of General Physiology, p. 359. Longmans, Green & 

 Co., 1924). He found in a large mollusc a salivary gland which produced sulphuric acid to a strength 

 of 4-5 per cent. 



3 Joffe, J. S.: New Jersey A gr. Exper. Sia., Bull. 3^4. 91pp. 1922. See, however, Brown, H. D.: 

 J. Am. Soc. Agrori., 15, 350-82. 1923; Jensen, H. L.: Centralhl. f. Bakieriol., Abt. II, 72, 242-46. 

 1927. 



■t Beijerinck, M. W.:Arch. d. Sci., E.xactes el Naliir. Haarlem (2d ser.), 9, 131-57- 1904; Ccnlralbl. 

 f. Bakieriol., Abt. II, 11, 592-99. See, however, Beijerinck, M. W.: Proc. Kon. Akad. v. Wetenschap- 

 pen, Amsterdam, 22, 899-908. 1920; Gehring, A.: Ccnlralbl. f. Bakieriol., Abt. II, 42, 402-38. 1915; 

 Lieske, R.: Jahr.f. Wiss. Bolan., 49, gi-127. 1911. 



