50 MICROBIAL CELL WALLS 



tained alanine, glutamic acid, DAP, glucosamine, and 

 muramic acid as principal constituents. Material of this 

 general composition was released from the wall on treat- 

 ment with T2 bacteriophage enzyme. Salton ^2 showed that 

 all but traces of the cell-wall DAP and muramic acid were 

 released into the soluble fraction when lysozyme acted on 

 the isolated walls of several Gram-negative bacteria, includ- 

 ing Escherichia coli. The composition of the soluble non- 

 dialyzable constituents released by lysozyme from the walls 

 of the Gram-negative bacteria showed that again alanine, 

 glutamic acid, DAP, and glucosamine were predominant 

 constituents with smaller amounts of muramic acid.22 



There seems little doubt now that the mucopeptide is the 

 component that is responsible for the structural rigidity of 

 the walls of Gram-negative bacteria, although it may ac- 

 count for as little as 10 to 20% of the weight of the 

 wall.i^'21.22 That the loss of the mucopeptide brings about 

 a collapse of the rigid cell-wall structure has been directly 

 demonstrated with isolated walls of Rhodospirillum rubrum 

 by the author. Figure \0a shows the appearance of R. ru- 

 brum walls before treatment with lysozyme, and Fig. 106 

 shows how the structures become spherical on incubation 

 with 100 jxg lysozyme per milliliter under conditions giv- 

 ing a release of mucopeptide constituents. ^2 The actual 

 amounts of mucopeptide in the walls of Gram-negative bac- 

 teria probably vary from one species to another, and the 

 data on amino sugar contents (Table 20) suggest that a 

 whole spectrum of mucopeptide contents exists.^* 



The bulk of the wall of at least a number of Gram-nega- 

 tive bacteria is made up of protein, lipid, and polysac- 

 charide complexes, undoubtedly forming the surface anti- 

 genic components. The cell walls isolated from Gram; 

 negative bacteria contain the monosaccharide constituents 

 that are characteristic of the purified lipo-polysaccharide 



