THE SULFUR BACTERIA 115 



Vogler and Umbreit considered the phosphate transfer, coupled with 

 sulfur oxidation and carbon dioxide fixation by B. thiooxidans, as a proof 

 that the combustion energy of sulfur is stored in the cells in the form of 

 phosphate bond energy. Of course, the observed transformation of one 

 phosphate molecule per 40 or 50 molecules of carbon dioxide cannot pro- 

 vide more than a small fraction of the energy required for chemosynthesis; 

 but Vogler and Umbreit considered it merely as an index of the inter- 

 cellular formation of high-energy phosphoric acid esters on a much larger 

 scale. 



If one refuses to consider the "delayed" carbon dioxide fixation by 

 sulfur bacteria as a carbohydrate synthesis, the energy calculations based 

 on this assumption lose their meaning. It is rather improbable that 

 sufficient energy for true chemosynthesis can be stored in the form of 

 "phosphate bond quanta" of 10 kcal per mole each (c/. Chapter 9, 

 page 226). 



One may suggest that the phosphate transfer and phosphorylation 

 have something to do with the primary reversible carbon dioxide fixation 

 (in chemosynthesis as well as in photosynthesis), rather than with the 

 reduction of carbon dioxide to carbohydrate (c/. Ruben's hypothesis, 

 page 201). 



The investigations of Vogler and Umbreit show how much information, 

 which may help in the understanding of the closely related phenomena 

 of chemosynthesis and photosynthesis, can be expected from a quanti- 

 tative study of the metabolism of autotrophic bacteria. 



Bacteria which oxidize sulfur by means of nitrate, instead of oxygen 

 (Thiobacillus denitrificans) , were discovered by Beijerinck in 1904. Since 

 0.8 mole of NOs" ions, reduced to nitrogen, are equivalent to one mole 

 of oxygen, we write the over-all equation as follows: 



(5.23) I (NOslaq. + § S + t\ HoO > ! (S04)aq. + A Haq. + f N2 + 86 kcal 



Thiosulfate Oxidizers. — Thiohacillus thioparus (Natansohn 1902) 

 oxidizes thiosulfate with the deposition of sulfur outside the cell. 



Natansohn assumed an intermediate formation of tetrathionate inside the cell, and a 

 subsequent external dismutation of tetrathionate into sulfur and sulfate; but Starkey 

 (1935) found no evidence of tetrathionate formation, and gave the following formulation 

 of the over-all reaction: 



(5.24) O2 + I (S203)a^. + i H2O )■ i (S04)i:<r. + S + 125 kcal 



Waksman and Starkey (1922) found a bacterium {Thiobacillus 

 novellus) which oxidizes thiosulfate to sulfate without the production 

 of sulfur: 



(5.25) O2 + h (S203)aq- + \ H2O > (SOO^. + Hii. + 109 kcal 



