630 YU. 1. SOROKIN 



fied by Bisset [30] as Chlamydobacteriales. Filamentous sulphur bacteria of the 

 genus Beggiatoa arc morphologically related to the blue-green algae Oscillatoria 

 [33], Finally, the autotrophic bacterium oxidizing carbon monoxide Bacterium 

 oligocarbophilum belongs to the Actinomycetes [34]. 



It is thus evident that as regards their morphological characteristics chemo- 

 synthetic organisms belong to the most highly organized forms of micro- 

 organisms. In fact, the bacterial forms of chemosynthetic microbes belong to 

 the genus Pseudomotîas, i.e. aerobic mobile bacteria known for their polyfer- 

 mentative capacities. The organisms of the Pseudomonas group possess a powerful 

 enzymic outfit which enables them to oxidize many organic substances hardly 

 accessible for other bacteria, such as hydrocarbons and cycUc compounds. 

 Undoubtedly this is the most elaborate and, from the evolutionary standpoint, 

 the most recent group of bacteria among the Eubacteriales. Filamentous 

 chemoautotrophic bacteria likewise belong to the higher representatives of 

 micro-organisms with a complex Hfe cycle. 



Adaptation to autotrophic metabolism has occurred repeatedly in the various 

 representatives of individual systematic groups of bacteria. This is borne out 

 by the narrow speciaHzation of chemoautotrophs belonging to different syste- 

 matic groups in relation to the mineral substrate which serves as the source of 

 energy- for the particular organism. 



Since the chemosynthetic bacteria emerged at advanced stages of the evolution 

 of micro-organisms, there have persisted forms which are intermediate between 

 autotrophic bacteria and heterotrophic ones. Thus, for instance, among the 

 sulphur bacteria there are the so-called 'obligatory' autotrophs which carmot 

 subsist without sulphur compounds and fail to assimilate organic matter [3]. 

 But there are also 'optionally' autotrophic sulphur bacteria which can dispense 

 with sulphur and assimilate organic substances [35]. Finally, there exist hetero- 

 trophic bacteria which oxidize sulphur compounds, but are incapable of effecting 

 chemosynthesis [2, 35]. Among the obligatory heterotrophs there occur bacteria 

 oxidizing ammonia [37]. Many heterotrophic bacteria inhabiting water basins 

 catalyse the oxidation of ferrous iron into ferric iron and accumulate iron 

 hydroxide in their cell walls [32]. Chemoautotrophic bacteria oxidizing hydrogen 

 also readily assimilate organic matter, and the assimilation of organic matter 

 may proceed in parallel with the oxidation of hydrogen [38]. The same pheno- 

 menon is also observed in desulphurizing bacteria, which may grow both auto- 

 trophically and hcterotrophically [24, 39]. 



Photosynthcsizing bacteria and green plants likewise readily assimilate organic 

 matter and can thrive at the expense of heterotrophic metabolism. The capacity 

 of autotrophic organisms for heterotrophic metabohsm, as Oparin justly pointed 

 out [14], is yet another proof of their secondary origin. The fact that the so-called 

 'strictly autotrophic' bacteria, such as sulphur-oxidizing bacteria and nitrifiers, 

 fail to assimilate organic matter from the medium does not at all prove that they 

 are incapable of oxidizing stored organic matter intracellularly by way of endo- 

 genous respiration. As a matter of fact, the available data prove that 'strict' 

 autotrophs possess the capacity for endogenous respiration at the expense of 

 oxidation of intracellular stores of organic matter [40, 41]. From our viewpoint, 



