28 MICROBIAL CELL WALLS 



of Gram-negative bacteria give strong support to the belief 

 that there are indeed two separate structures, a complex wall 

 and a membrane.^^'^^-^^ (See Fig. 7.) It appears likely, 

 then, that the differences in wall composition between the 

 Gram-positive and Gram-negative bacteria amply demon- 

 strated in many investigations ^^-^^'^^ are real and are not 

 an artifact of a major structural difference between the two 

 groups of organisms. What is worth emphasizing here is 

 that both groups of organisms possess mucopeptide con- 

 stituents in common, a finding that has led to the idea of 

 a "basal" structure being present in all bacterial cell walls 

 (Work 20). The nature of the basal structure has become 

 more apparent, and it is likely that one of a variety of 

 mucopeptides can perform this function. ^i' 22 What is 

 uncertain at the moment is the variety of monomeric con- 

 stituents in the mucopeptides from both Gram-positive and 

 Gram-negative bacterial walls. At the present time there 

 is insufficient evidence to suggest that the term "basal struc- 

 ture" means any more than a class of mucopeptides con- 

 taining some common building units of amino sugars and 

 amino acids. 



Constituents of Walls of Gram-Positive Bacteria 



Analysis of the walls of Gram-positive bacteria revealed 

 the presence of both nitrogen and phosphorus, and in Bacil- 

 lus suhtilis walls the content of P was very high.^s Qn 

 hydrolysis the walls contained reducing substances and 

 amino sugars, and some of the typical results are shown, 

 together with N and P determinations, in Table 9. 



The first fascinating detail to emerge from the early 

 studies of cell-wall chemistry was the small variety of amino 

 acids in the walls of some bacteria. ^^ Thus the wall of 

 Micrococcus lysodeikticus isolated by mechanical disintegra- 

 tion and receiving no treatments other than washing with 



