628 YU. I. SOROKIN 



later than photoautotrophic bacteria, since their coming into being is dependent 

 on the accumulation of free oxygen in the atmosphere at the expense of photo- 

 synthesis. One of the chief arguments proving the secondary origin of auto- 

 trophic bacteria, as compared to heterotrophic ones, is that the capacity for 

 building up their body entirely out of simple mineral compounds requires a 

 more complex biochemical organization of the cell than does hfe involving the 

 assimilation of ready organic matter [15, 1 6]. This assumption has been brilliantly 

 confirmed in a great number of papers on the biochemistry of metabolism in 

 chemoautotrophic bacteria [13, 17]. It was found that even the cells of the so- 

 called 'obHgatory' chemoautotrophs (sulphur bacteria, nitrifiers) do not differ, as 

 regards the complexity of their biochemical organization, from the cells of the 

 most highly perfected types of aerobic heterotrophic micro-organisms. The same 

 amino acids enter into the composition of the protein of chemoautotrophic 

 bacteria as into the composition of the protein of other living organisms [18]. All 

 the water-soluble vitamins and other important biologically active compounds 

 are found in their cells [3, 19]. It has been established by a number of investi- 

 gations that the oxidation of mineral substances (NH4+, S and H2) proceeds in 

 the cells of chemosynthetics under the influence of the same enzymic systems 

 which participate in the process of respiration in heterotrophic bacteria and in 

 other more highly organized beings. Thus, cytochromes were found in the nitri- 

 fying microbe Nitrosomonas [20]. Pyridine dehydrogenases, cytochromes and 

 even a glycolytic mechanism effecting the decomposition of intracellular reserve 

 polysaccharide were found in the cells of another 'obligatory' chemosynthetic 

 organism, Thiobacillus thiooxidans [3]. In hydrogen bacteria and sulphate- 

 reducing bacteria the oxidation of hydrogen is carried on by the iron-containing 

 enzyme, hydrogenase [2]. Other data, further, lead to the conclusion that a 

 dicarboxylic acid system participates in the oxidative metabolism of chemo- 

 autotrophic bacteria [21]. 



The binding of the energy liberated in the course of oxidation of mineral 

 substances in chemosynthesis and its utilization for synthetic processes proceeds 

 in chemoautotrophic bacteria with the aid of the same biochemical mechanisms 

 as in heterotrophic bacteria. The oxidation of mineral substances in chemo- 

 synthetic organisms occurs intracellularly and is associated with phosphorylation. 

 In this case the oxidation energy is captured and bound as chemical-bond energy 

 in phosphorus compounds. These may yield the energy concentrated in them 

 for the assimilation of CO2 in chemosynthesis. Such a mechanism was revealed 

 in Thiobacillus thiooxidans [22], in hydrogen bacteria [23] and in sulphate- 

 reducing bacteria [24], Phosphorylation in chemoautotrophs proceeds with the 

 aid of the system adenosine triphosphate ?^ adenosine diphosphate [23, 35, 26]. 



The above-quoted data show that with regard to complexity of their bio- 

 chemical organization, chemosynthesizing bacteria are not inferior to aerobic 

 heterotrophs. It may be assumed that they even exceed the latter in this respect, 

 since heterotrophic bacteria are devoid of the capacity for autotrophic nutrition, 

 whereas most chemoautotrophic bacteria (and on the intracellular level probably 

 all of them, owing to endogenous respiration) are capable of decomposing organic 

 matter and feeding on it. Biochemical studies of chemosynthetic microbes have 



