THE CHEMICAL CONSTITUTION OF BACTERIAL CELLS 43 



There is general agreement that a high proportion of the total ash consists of 

 phosphoric acid, 10-45 per cent, or more reckoned as P2O5 among most bacterial 

 species, 40-70 per cent, or more among the acid-fast forms (see Tamura 19136, 

 Buchanan and Fulmer 1928-30). Among the mineral constituents that have been 

 identified are Ca, Mg, Fe, Na, K and the CI and SO4 ions. 



The Protein and other Nitrogenous Constituents of Bacteria. — The recorded 

 figures for total nitrogen are widely discrepant. Buchanan and Fulmer quote 

 figures varying between 1-8 and 15 per cent, of dry bacterial substance ; and 

 the percentages recorded by different observers for the same bacterial species 

 show little agreement. The usual range would appear to be from 8 to 15 per cent. 

 Nicolle and Alilaire's figures vary only between 8-28 and 10-79 per cent., but 

 recent determinations carried out by Linton, Mitra and Shrivastava (1934) on 

 the cholera vibrio give values of 12-17-15-57 per cent. 



In regard to the nature and amount of the coagulable proteins of bacterial cells our 

 knowledge is curiously scanty. Boivin and Mesrobeanu (1934), who record a total N figure 

 of 13-70 per cent, dry weight for Bad. coli, find that only 0-65 per cent, of this nitrogen, 

 reckoned on the same basis, is soluble in trichloracetic acid, the remaining 13-05 per cent 

 being precipitated. Their figures for other organisms vary over a considerable range, 

 but in every case the nitrogen precipitated by trichloracetic acid forms more than 80 per 

 cent, of the total. It should be noted that acids will precipitate most forms of macro- 

 molecular nitrogen from solutions containing precipitable proteins. The separation of 

 proteins from such mixtures has seldom been attempted, but Linton, Mitra and Shrivastava 

 (1934) I'ecord in the case of V. cholerce that the coagulable protein is almost all in the form 

 of globuhn, i.e. is precipitated by half-saturation with ammonium sulphate. As regards 

 the non- coagulable nitrogen, Boivin and Mesrobeanu calculate that about a quarter is 

 present as polypeptides or amino-acids, and about another quarter as ammonium com- 

 pounds. The percentages faUing in these categories vary over a considerable range. 



We have more information in regard to the units of which bacterial protein is built 

 up ; and these seem, in general, to be the same as those that constitute proteins of other 

 Uving cells. Numerous observers have carried out estimations by the methods of van 

 Slyke, and the results show fair general agreement, though indicating significant differences 

 in the proteins of different species. Thus, to take a few Ulustrative examples, in acid- 

 fast baciUi, Tamura (19136) has reported that 63-62-66-74 per cent, of the total nitrogen 

 is present as mono-amino-acid-nitrogen, 13-71-15-21 per cent, as basic amino-acid-nitrogen, 

 while Johnson and CoghiU (1925) record 47-39-5210 per cent, and 11-35-14-43 per cent, 

 for the tubercle bacillus. For the diphtheria bacillus Tamura (1914) gives corresponding 

 figures of 54-62 per cent, and 16-89 per cent., Hirsch (1931) gives 44-80-47-41 per cent, 

 and 16-67-17-67 per cent. For Bacf. coli Eckstein and Soule (1931) give 42-90-45-71 

 per cent, and 16-45-19-82 per cent., and for V. cholerce, Linton, Mitra and Shrivastava 

 (1934) give 54-84-5711 per cent, and 24-08-2603 per cent. These figures, it may be noted, 

 refer to the total nitrogen present in the mono-amino and basic amino-acids, not to the 

 nitrogen present in the amino form. Among the amino-acids that have been identified in 

 bacterial proteins, arginine, histidine, lysine and tyrosine appear to be almost always 

 present ; leucine and tryptophan have both been frequently demonstrated. The figiu-es for 

 cystine vary ; some observers have failed to demonstrate its presence, others have found it 

 in relatively smaU amounts. There seems httle doubt that the relative proportions of 

 different amino-acids in different bacterial proteins vary significantly. Thus Tamura 

 (1913a) records the presence of relatively large amounts of ^phenylalanine in the proteins 

 of an acid-fast bacillus; while (1914) he failed to identify this acid in the proteins of 

 the diphtheria bacillus, which contained an unusuaUy large amount of tyrosine. The 

 capsule of the anthrax baciUus contains a large amount of a polypeptide which on hydro- 

 lysis yields rf(-)-glutamic acid in a state of almost chemical purity (Ivanovics and Bruckner 



