Abstract
Background: A future bioeconomy relies on the efficient use of renewable
resources for energy and material product supply. In this context,
biorefineries have been developed and play a key role in converting
lignocellulosic residues. Although a holistic use of the biomass feed is
desired, side streams evoke in current biorefinery approaches. To ensure
profitability, efficiency, and sustainability of the overall conversion
process, a meaningful valorization of these materials is needed. Here, a
so far unexploited side stream derived from fast pyrolysis of wheat
straw-pyrolysis water-was used for production of 1,2-propanediol in
microbial fermentation with engineered Corynebacterium glutamicum.
Results: A protocol for pretreatment of pyrolysis water was established
and enabled growth on its major constituents, acetate and acetol, with
rates up to 0.36 +/- 0.04 h(-1). To convert acetol to 1,2-propanediol,
the plasmid pJULgldA expressing the glycerol dehydrogenase from
Escherichia coli was introduced into C. glutamicum. 1,2-propanediol was
formed in a growth-coupled biotransformation and production was further
increased by construction of C. glutamicum.pqo.aceE.ldhA.mdh pJULgldA.
In a two-phase aerobic/microaerobic fed-batch process with pyrolysis
water as substrate, this strain produced 18.3 +/- 1.2 mM 1,2-propanediol
with a yield of 0.96 +/- 0.05 mol 1,2-propanediol per mol acetol and
showed an overall volumetric productivity of 1.4 +/- 0.1 mmol
1,2-propanediol -L-1 h(-1).
Conclusions: This study implements microbial fermentation into a
biorefinery based on pyrolytic liquefaction of lignocellulosic biomass
and accesses a novel value chain by valorizing the side stream pyrolysis
water for 1,2-PDO production with engineered C. glutamicum. The
established bioprocess operated at maximal product yield and
accomplished the so far highest overall volumetric productivity for
microbial 1,2-PDO production with an engineered producer strain.
Besides, the results highlight the potential of microbial conversion of
this biorefinery side stream to other valuable products.
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