COMPOSITION OF MICROBIAL AMINO ACID POOLS 93 
following discussion, only illustrative examples of such observations will be presented 
and no attempt will be made to treat the subject exhaustively. This section will deal 
largely with cultural and metabolic factors which influence pool composition. Studies 
on the effects of disruptive chemical and physical forces which pertain more closely 
to the question of the intracellular state of the pool will be dealt with separately. 
Effect of age 
Growth of gram-positive and -negative bacteria is completed generally within 24 h 
of incubation. In most studies with gram-positive bacteria the total pool size is rela- 
tively constant during this period of cultivation, especially towards the end of the 
exponential growth phase!’ ®. 7, although in some cases, a slight drop in the early 
portion of the exponential growth phase has been reported’!. Compensatory changes 
in the levels of individual amino acids may occur which in summation give the im- 
pression, of a relatively constant pool’®: 73. The difficulties in formulating generaliza- 
tions can be seen by comparing Figs. 5-10, 11-16, and 17—22 which show the extrac- 
table pool of L. avabinosus, Leuco. mesenteroides and S. faecalis at various times of incu- 
bation in the same growth medium. In all cases growth was completed within 24 h of 
incubation. L. avabinosus had a large, varied pool very early in the exponential phase 
which remained relatively constant except for the appearance of y-aminobutyric acid 
until the end of the active growth phase after which it declined sharply. With Leuco. 

Figs. 5-10. Free amino acid pool of L. avabinosus 17-5, grown for varying times in a defined medium 
containing acid hydrolyzed casein. Incubation times were as follows: Fig. 5, 12 h; Fig. 6, 16h; 
Fig. 7, 22 h; Fig. 8, 39 h; Fig. 9, 68 h; Fig. 10, too h. Maximum cell density was attained between 
16 and 22 h. Chromatograms prepared using hot water extracts from 6.6 mg d.w. of cells. Chro- 
matographic solvents: first direction, right to left, phenol, NH,, H,O; second direction, bottom 
to top, lutidine, H,O. The substance indicated in Fig. 7 is y-aminobutyric acid. 
References p. 105/108 
