410 FURTHER EVOLUTION 



reveals the presence, alongside these oxidative mechanisms, 

 of the same enzymic complexes which form the basis of the 

 heterotrophic and anaerobic metabolism of all other living 

 things. This is what allows many chemoautotrophs to go over 

 readily to a heterotrophic way of life under certain circum- 

 stances. 



Actually, facts have been assembled in the scientific litera- 

 ture for a comparatively long time indicating that many 

 organisms which can exist as pure chemoautotrophs can, at 

 the same time, assimilate organic substances very well. This 

 was established for hydrogen bacteria as early as 1910 by 

 A. Lebedev^^ and was later confirmed by W. Ruhland.''^ K. 

 Trautwein^* and R. L. Starkey^^ working with Thiobacillus 

 trautweinii, and P. A. Roelofsen^^ and M. S. Cataldi^^ 

 working with other sulphur bacteria, showed that these can 

 grow heterotrophically in the absence of oxidisable inorganic 

 substrates and in the presence of the organic substances 

 which they require. The same was established for many iron 

 bacteria by the experiments of H. Molisch,^^ R. Lieske,^^ 

 M. S. Cataldi,*° V. O. Kalinenko" and others. 



In presenting an account of the extensive experimental 

 evidence which has now been collected, C. B. van Niel*^ 

 reaches the conclusion that organic substances have a less 

 deleterious effect on most chemosynthetic bacteria than is 

 commonly supposed. Only Nitrosomonas, Nitrobacter, four 

 species of Thiobacillus (in particular T. thiooxidans and 

 T. thioparus) and forms related to these species can be con- 

 sidered as ' strict ' autotrophs (and this only in a somewhat 

 provisional sense). All the other chemoautotrophs, according 

 to van Niel, are not obligate autotrophs but can make 

 extensive use of the energy of organic compounds. 



However, it has recently been established that even those 

 few species of chemoautotrophs {Thiobacillus thiooxidans 

 and the nitrifiers) which, for reasons which are still unknown, 

 cannot assimilate the organic substances contained in the 

 surrounding medium, can nevertheless carry out internal 

 respiration which proceeds by the oxidation of polysacchar- 

 ides which they have accumulated within their cells. These 

 transformations are brought about by the same glycolytic 

 mechanisms which operate in typical heterotrophs.*^- ^* This 



