THE STUDY OF BACTERIAL METABOLISM 45 



as starch or glycogen, but of the significance of these intracellular granules we 

 know little, and their exact nature is still in dispute. 



Bacterial Fats, Lipins and Waxes. — Buchanan and Fulmer quote figures 

 ranging from l-56-'i(>8 per cent, dry weight for the ether-extractable substances 

 in various species of bacteria. NicoUe and Alilaire record percentages of 6-31-15-77 

 for acetone-extractable substances, but the range of species covered is not the 

 same. Lipin values of less than 10 per cent, have been recorded for certain mem- 

 bers of the Salmonella group (Williams, Bloor and Sandholzer 1939), of 5-6 per cent., 

 for Brucella (Stahl and Hamann 1941) and of 10-14 per cent, for the gonococcus 

 (Stokinger et al. 1944). There is no doubt that the production of particular lipins 

 or waxes characterizes particular bacterial species. We have, for instance, noted 

 in the previous chapter the production by the tubercle bacillus of a wax on which 

 its acid-fastness depends (see also Chapter 16). We know so little of the part 

 played by fats, lipins and waxes in the economy of the bacterial cell that, for the 

 moment, it will suffice to note their presence. For such data as are available in 

 regard to their chemical constitution reference may be made to Buchanan and 

 Fulmer (1928-30). 

 The Study of Bacterial Metabolism. 



In the study of bacterial metabolism, whether we are concerned with sub- 

 stances utilized by bacteria as sources of food or energy, with the products of 

 metabolism, or with the mechanisms by which dissimilation and assimilation of 

 foodstuffs is achieved, the most striking feature is the extreme diversity of bacterial 

 activity. It is possible to give a generalized description of metabolism that will 

 apply with minor modifications to the nutrition of all the higher animals, but in 

 bacteria, the diverse metabolic activities appear to have been evolved by adapta- 

 tion to the widest variety of environmental conditions ; so that one species or 

 another can take advantage of almost any thermodynamically suitable type of 

 foodstuff and any moist environment within a temperature range rather wider 

 than that suitable for most other groups of organisms. Certain groups of bacteria, 

 however, share a sufficient similarity of metabolic activities as to make them 

 suitable for discussion in an introduction to the subject of bacterial metabolism. 

 Among these are the bacteria that primarily interest the medical bacteriologist, 

 and we shall endeavour to select these for illustrative examples. The studies of 

 the kind that concern us have, for the most part, been carried out by biochemists, 

 and mark the rapid development of microbiological chemistry as a distinctive branch 

 of biological science. Although work in this field was initiated by Pasteur, and 

 developed extensively by him within the limits of the chemical knowledge and tech- 

 nique of his time, it has been largely neglected by his bacteriological successors. 

 These have, for the most part, been content to use the bacterial fermentation reac- 

 tions as diagnostic tools, without inquiring in any systematic way into the actual 

 chemical changes concerned. The common practice has been to map out the fermen- 

 tative abilities of different bacterial species, using an arbitrarily selected series of 

 carbohydrate and other substrates which experience has shown to possess differential 

 value, and noting the production of acid by a colour change in a suitable indicator, 

 or the production of gas by observing its collection within a small inverted tube 

 contained in the culture medium. The study of the changes produced in nitro- 

 genous substrates has been even more limited and arbitrary — the production of 

 indole from a tryptophan-containing substrate, the production of H2S from sulphur- 

 containing amino-acids, and so on. This neglect has been natural enough. The 



