d-Glucaric acid (GA), one of the polyhydroxy dicarboxylic
acids, is known for its great potentials in the polymer, food, detergent,
and pharmaceutical industries. Here, we presented a highly efficient
synthesis of GA from starch by in vitro biotransformation (ivBT).
This one-pot ivBT was composed of five thermophilic enzymes (i.e.,
isoamylase, α-glucan phosphorylase, phosphoglucomutase, inositol
1-phosphate synthase, and inositol monophosphatase) responsible for
the synthesis of myo-inositol (MI) from starch, followed
by three mesophilic enzymes (i.e., myo-inositol oxygenase
(MIOX), uronate dehydrogenase (UDH), and H2O-forming NADH
oxidase (NOX)) responsible for the synthesis of GA from inositol.
Also, a stepwise-added enzyme cocktail strategy was employed to circumvent
the inhibition of GA on MIOX and mismatches in enzymes’ properties,
such as temperature and pH. The three-step cascade bioprocessing in
one pot resulted in the concentration of disodium glucarate of approximately
9.66 g/L (i.e., 38 mM) from 10 g/L maltodextrin with an atom efficiency
of 96.6%. Up to 52.1 g/L disodium d-glucarate, the highest
titer reported, was produced in a stirred bioreactor operated in two-reaction
temperature ranges, featured with the stepwise addition of enzyme
cocktails, and equipped with a constant pH controller and stirring
for enough oxygen supplies. This study could open a new door to the
industrial biomanufacturing of GA by ivBT.