152 PLANT RESPIRATION 



bacteria. p The respiration of Beggiatoa consists in the oxida- 

 tion of hydrogen sulphide, first to molecular sulphur and then 

 to sulphuric acid: 



(I) H2S + O = HoO + S 



(II) S + 3O = SO3 



The oxidation of one molecule of H2S to H2SO4 releases 115 

 Calories of heat. 



The thiosulphate bacteria discovered by Nathansohn^ also 

 grow without any organic nutrient. As respiration they make 

 use of the following reaction :« 



aNa.SoOs + 5O2 = 4Na2S04 + 2Na2S406. 



This oxidation releases considerable energy. The iron bac- 

 teria oxidise ferrous salts to ferric salts. This exothermic 

 process serves as respiration for them,^ for they can be grown 

 on purely mineral solutions. The hydrogen bacteria^ also 

 respire on the basis of the combustion of hydrogen: 



2H2 + O2 = 2H0O, 



and are able to utilize the resultant free energy for the assimila- 

 tion of the atmospheric carbon dioxide. As for the methane 

 bacteria,^ they oxidise methane to CO2 and water, so it is uncer- 

 tain whether this process is to be thought of as a direct oxidation 

 or as an ordinary sugar respiration. That is to say, methane 

 could serve as material for the synthesis of sugar. Still we 



1 Nathansohn. Mitt. d. Zool. Stat. Neapel. 15: 655. 1902; Beijerinck. Zentralbl. f. 

 Bakt., Parasitenk. u. Infektionskrankh. (II). 11: 593- 1904. 



2 Winogradski, S. Bot. Zeitschr. 46: 261. 1888; Lieske, R. Jahrb. f. wiss. Bot. 49: 

 91. 1911; so: 328. 1912; Zentralbl. f. Bakt., Parasitenk. u. Infektionskrankh. (II). 49: 

 413. 1919. [See also Cholodny, N. Die Eisenbacterien, Beitrage zu einer Monographie. 

 Jena. 1926.] 



3 Sohngen. Zentralbl. f. Bakt., Parasitenk. u. Infektionskrankh. (ID. 15: SU- 1906; 

 Kaserer. Ibid. 15:575. 1906; 16: 681, 769. 1906; Lebedew, A. v. Biochem. Z. 7: i- 

 1908; Niklewski. Jahrb. f. wiss. Bot. 48: 113. 1910; Zentralbl. f. Bakt., Parasitenk. u. 

 Infektionskrankh. (II). 20: 469. 1908. 



* Sohngen. loc. cii.; Kaserer. loc. cti. 



p An exceptional case is that of Thiobacillus thiooxidans which does use small 

 amounts of glucose but only in the presence of sulphur. Its nitrogen is obtained 

 only from ammonium salts. Cf. R. L. Starkey. Jour. Bact. 10: 135-195. 

 1925. — Ed. 



1 A facultative carbon autotropic form was found by Trautwein (Centralbl. 

 Bakt. (,11). 53: 513-560. 1921) which gives as the product of oxidation either 

 a sulphate, a dithionate or a tetrathionate. — Ed. 



