FIRST HETEROTROPHS AND ANAEROBES 413 



organisms use the hydrocarbons obtained from these mixtures 

 as their sole sources of carbon and of energy. From a study 

 of these organisms Tauson^* came to the conclusion that their 

 inability to use glucose, fructose, mannitol, glycerol, tartaric 

 acid and other similar compounds, which serve as satisfactory 

 sources of carbon for most living things, was due to their 

 inability to transform the primary alcohol groups into methyl 

 groups. Thus the ' cyclists ' (like other hydrocarbon-using 

 organisms) cannot form acetaldehyde from carbohydrates and 

 this prevents them from being able to synthesise fatty acids 

 and the carbon skeletons of amino acids. They use another 

 means to this end, namely the breakdown of the benzene 

 nucleus of cyclic compounds, and thus obtain only partly 

 hydroxylated carbon chains which then serve as material for 

 the building of the proteins and lipids of protoplasm. This 

 suggestion of Tauson's certainly still requires further study 

 and biochemical confirmation. 



However, even if we accept Tauson's views, it is still hard 

 to decide whether this metabolic peculiarity is, as Tauson 

 thought, an expression of the primitiveness of the ' cyclists ', 

 or whether it arose secondarily as an adaptation to circum- 

 stances in which hydrocarbons were the most readily avail- 

 able nutrients. The latter is the more probable. In the first 

 place this is suggested by the extensive material put forward 

 by C. E. Zobell,^^ which shows that among hydrocarbon- 

 using organisms there are living things belonging to very 

 diverse systematic groups including bacteria, yeasts and 

 moulds. Another fact which suggests that the ability of these 

 organisms to use hydrocarbons as nutrients is of secondary 

 origin is their pronounced aerobic habit, though some of 

 them can also exist without free oxygen. As an example we 

 may here cite Tauson's work on Microspira spp.®° Under 

 strictly anaerobic conditions (in the deep layers of the crust 

 of the Earth) these organisms can oxidise paraffins as well as 

 naphthalene, phenanthrene and other polycyclic compounds 

 while simultaneously reducing sulphates to hydrogen sul- 

 phide. 



Although the metabolism of hydrocarbon-using organisms 

 has received very little study as yet, one can nevertheless find 

 in them the general methods of transformation of organic 



