COMPOSITION OF MICROBIAL AMINO ACID POOLS 97 
lation systems. However, the form in which inorganic nitrogen is provided also can 
influence the content of the pool!*!, 1%, The effect of providing nitrogen as a single 
amino acid has been a popular experiment with obvious origins in earlier explorations 
of nitrogen assimilation in microorganisms. Numerous changes in qualitative pool 
composition are usually observed as shown for Aspergillus oryzae by SIMONART AND 
Cuow!®3, Table XI taken in modified form from this work shows the markedly different 
amino acid-pool composition that can be found depending on the amino acid used to 
support growth. Speculations concerning the reasons for such differences involve 
predictions from the known operation of the tricarboxylic acid cycle and the amino 
acid transaminases. Conversely, such observations show that when the potential 
enzymatic activity of an organism is known, observations of the fluctuating content 
of the pool can be applied to detect the shifting balance in reaction rates affecting 
different pool components. 
Although less frequently studied, variations in the source of carbon also produce 
changes in the composition of the pool. For example, SIMONART AND CHow'!® observed 
striking differences when a variety of dicarboxylic acids were used. Most investigators 
have encountered quantitative rather than qualitative changes in the pool? ”. It 
should be noted that when an organic form of nitrogen is provided, the organism in 
effect is also supplied with considerable quantities of a new carbon source. 
The effect of nutritional deficiencies on pool composition has received surprisingly 
little attention. GALE noted a reduction in pool level when S. faecalis was grown in 
media containing minimal amounts of required amino acids. However, the amount of 
amino acid provided sufficed to support protein synthesis and growth, and the changes 
noted probably reflected reduced accumulation of exogenous amino acids. Indeed, 
interference with protein synthesis appears from the work of MANDELSTAM!!® and 
HANCOCK” to increase the amounts of amino acids in the pool. The effects of vitamin 
deficiency on various properties of the lactic acid bacteria including pool composition 
and amino acid transport have been studied in this laboratory. Figs. 23—28 illustrate 
the effects of a vitamin B, deficiency on the pool of L. avabinosus. At the end of active 
growth nutritionally normal cells form y-aminobutyric acid, whereas vitamin B,-de- 
ficient cells do not, an observation which corresponds to the lack of glutamic acid 
decarboxylase activity in the latter cells. On the other hand, the pool in B,-deficient 
cells contains three unknown substances not found in normal cells. Incubation of nor- 
mal cells with isonicotinic acid hydrazide induces the appearance of these substances in 
smaller quantities. In addition, biotin-deficient cells accumulate an unidentified sub- 
stance having the chromatographic properties of diaminopimelic acid. Observations 
such as these, of course, remain interesting curiosities unless the substances found are 
identified unequivocally and the metabolic basis for their appearance in the pool 
established by enzymatic studies. 
Effect of incubation in nutritionally incomplete media 
One of the most extensive investigations of this type has been carried out with S. 
cerevisiae by HALVORSON, SPIEGELMAN et al. (cf. refs. 70, 172). Incubation of the yeast 
in a nitrogen-free medium leads to depletion of the pool, but only when a metabolizable 
carbon source is provided. Inhibition of energy production prevents this loss, and 
provision of a poorly utilized carbon source can promote increases in pool levels. The 
References p. 105/108 
