116 PHOTO- AND CHEMOSYNTHESIS OF BACTERIA CHAP. 5 



A third kind of thiosulfate-oxidizing bacteria uses nitrate instead of 

 oxygen (Lieske 1912): 



(5.26) i (N03)aq. + h (S203)a<r. + ^ H2O > (S04)rq-. + f N2 + 



i Hjq. + 97 kcal 



Thiocyanate Oxidizers. — Happold and Key (1937) discovered the 

 Bacillus thiocyan-oxidans, which catalyzes the reaction: 



(5.27) O2 + h (CNS)rq. + H2O > I (S04)aq- + i (NH4):q. + I CO2 + 112 kcal 



(c) The Iron Bacteria (Vinogradsky 1888) 



These organisms precipitate ferric hydroxide from waters containing 

 ferrous salts, and are responsible for the red color of many natural 

 waters. Their chemical activity can be represented by the equation: 



(5.28) O2 + 4 Fe+qt + 2 H2O > 4 Fe^qt^ + 4 (OH)aq. + 37 kcal 



The gain in energy becomes larger if we include in the equation the 

 precipitation of ferric hydroxide (c/. Lieske 1911, 1919): 



(5.29) O2 + 4 Fe+qt + 10 H2O > 4 Fe(0H)3 + 8 H+q. + 63 kcal 



(d) The Hydrogen Bacteria 



Bacillus pantotrophus, discovered by Kaserer in 1906, and a number 

 of similar microorganisms of the soil, are heterotrophants which are, 

 however, capable of survival and growth in purely inorganic media, if 

 they are provided with molecular hydrogen, in addition to oxygen and 

 carbon dioxide. Their metabolism is based, under these conditions, on 

 the energy of oxidation of hydrogen to water ("oxyhydrogen reaction"): 



(5.30) O2 + 2 H2 > 2 H2O + 137 kcal 



— hence the name "Knallgas bacteria" suggested by Ruhland (1924). 

 Reaction (5.30) is coupled with the reduction of carbon dioxide to organic 

 matter, and further complicated by the simultaneous respiration, i. e., 

 autoxidation of cell material. (Some autotrophic bacteria, the Nitro- 

 somonas, for example, apparently dispense with ordinary respiration 

 altogether, their energy requirements being covered entirely by the 

 oxidation of the inorganic substrate.) 



The investigations of Kaserer (1906), Nabokich and Lebedev (1907), 

 Lebedev (1908, 1909) and particularly Niklevsky (1908, 1910) have 

 shown a wide distribution of normally heterotrophic but potentially 

 hydrogen-oxidizing bacteria in all soils. Some of them appear to be 

 capable of using nitrate, nitrous oxide or even sulfate as oxidants instead 

 of oxygen, but not much is known about these reactions. Only one 

 species. Bacillus picnoticus, has been thoroughly investigated by Ruhland 

 (1924); and because these hydrogen bacteria appear to be the simplest 



