432 FURTHER EVOLUTION 



phosphate into trioses and then, via pyruvic acid and acet- 

 aldehyde, into acetic acid. If it is short of oxygen, however, 

 it begins to carry out ordinary alcoholic fermentation as it 

 has all the necessary enzymes. 



When grown on a mineral medium with the addition of 

 glucose, Bacillus subtilis cannot carry out alcoholic fermenta- 

 tion and is obliged to exist aerobically. However, as N. D. 

 Gary and R. C. Bard^°^ showed, a culture of these bacteria, 

 grown on a medium containing glucose, tryptone and yeast 

 extract, grows under anaerobic conditions by carrying out 

 lactic acid fermentation. In such a culture one may find a 

 collection of the most important glycolytic enzymes. 



Even in such well-defined aerobes as the obligate chemo- 

 autotrophs, in which the whole mechanism is directed 

 towards the oxidation of an inorganic substrate by oxygen, 

 there have been found, as we saw above, such typical glyco- 

 lytic mechanisms and intermediate products as diphospho- 

 pyridine nucleotide, ATP, phosphohexoses and phospho- 

 trioses. 



Thus we see that among bacteria, which are the organisms 

 manifesting the greatest metabolic variety, we find every- 

 where that their metabolism is based on anaerobic degrada- 

 tion which follows the scheme for alcoholic fermentation. 

 This seems to be completely universal among these micro- 

 organisms. Only isolated groups of bacteria possess the 

 supplementary oxidative mechanisms, which must, obviously, 

 have arisen after the appearance of free oxygen in the atmo- 

 sphere of the Earth. The oxidative decarboxylation of pyruvic 

 acid by lactic acid bacteria may serve as an example of such 

 an original primitive mechanism. Later these mechanisms 

 became more complicated and were transformed into whole 

 cycles of orderly oxidative reactions which will be analysed 

 in more detail later, in connection with the problem of the 

 origin of respiration. 



The glycolytic breakdown of carbohydrates also underlies 

 the energy metabolism of other primitive living things, in 

 particular protozoa. A. LwofF and his colleagues^"® found a 

 starch phosphorylase in Polytoma caeca. Adenosine mono-, di- 

 and triphosphates, glucose- 1 -phosphate, fructose-6-phosphate, 

 fructose- i:6-disphosphate and phosphogly eerie acid have all 



