the
maximum specific production rate of 4-hydroxybutyrate
(4HB) was obtained. Thus, the synthesis of 3HB was
growth-limited production under nitrogen-deficient condition,
whereas the synthesis of 4HB was growth-associated
production under nitrogen-sufficient condition. The mole
fraction of 4HB units increased proportionally as the ratio
of c–hydroxybutyric acid in the feed medium increased at
any value of C/N ratio. Based on these kinetic studies, a
simple strategy to improve P(3HB-co-4HB) production in
shake flask fed-batch cultivation was investigated using C/
N and substrate feeding ratio as manipulating variable, and
was successfully proved by the experiments.