However, the total amount of glutamate including glutamate unit
in γ -PGA and residual glutamate in broth was much more than the
added glutamate, and increased with the KCl concentration. It was
deduced that the substrate of γ -PGA came from two parts: one is
from extracellular glutamate which exists in the medium by artificial added, and others derived from intracellular glutamate which
obtained via glycolysis and the tricarboxylic acid cycle by glucose.
Based on above results, it was speculated that glucose was mainly
used for cell growth and little was used to participate in γ -PGA
synthesis when the culture contained low concentration KCl, but
more glucose was involved in γ -PGA synthesis when the concentration of KCl increased. Therefore, addition of KCl can be used as
a control strategy to improve γ -PGA yield by enhancing the conversion rate of carbon source