Integration of pH Control into Chi.Bio Reactors and Demonstration with Small-Scale Enzymatic Poly(ethylene terephthalate) Hydrolysis

Small-scale bioreactors
that are affordable and accessible
would
be of major benefit to the research community. In previous work, an
open-source, automated bioreactor system was designed to operate up
to the 30 mL scale with online optical monitoring, stirring, and temperature
control, and this system, dubbed Chi.Bio, is now commercially available
at a cost that is typically 1–2 orders of magnitude less than
commercial bioreactors. In this work, we further expand the capabilities
of the Chi.Bio system by enabling continuous pH monitoring and control
through hardware and software modifications. For hardware modifications,
we sourced low-cost, commercial pH circuits and made straightforward
modifications to the Chi.Bio head plate to enable continuous pH monitoring.
For software integration, we introduced closed-loop feedback control
of the pH measured inside the Chi.Bio reactors and integrated a pH-control
module into the existing Chi.Bio user interface. We demonstrated the
utility of pH control through the small-scale depolymerization of
the synthetic polyester, poly(ethylene terephthalate) (PET), using
a benchmark cutinase enzyme, and compared this to 250 mL bioreactor
hydrolysis reactions. The results in terms of PET conversion and rate,
measured both by base addition and product release profiles, are statistically
equivalent, with the Chi.Bio system allowing for a 20-fold reduction
of purified enzyme required relative to the 250 mL bioreactor setup.
Through inexpensive modifications, the ability to conduct pH control
in Chi.Bio reactors widens the potential slate of biochemical reactions
and biological cultivations for study in this system, and may also
be adapted for use in other bioreactor platforms.