Abstract
BackgroundA 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.ResultsA 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 Δpqo ΔaceE ΔldhA Δmdh 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.ConclusionsThis 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.
Highlights
A future bioeconomy relies on the efficient use of renewable resources for energy and material product supply
Additional file 1: Figure S1) and observed the highest buffer capacity close to the p Ka of acetic acid. This indicates that acetate predominantly accounts for the low initial pH of about 2.5 of crude pyrolysis water (PW) and represents the major buffering entity. It was previously reported for bio-oils derived from fast pyrolysis that volatile acids are responsible for 60–70% of the total acidity [51]
This study describes the access to a novel value chain implementing microbial fermentation into biorefineries, by using the unexploited side stream pyrolysis water derived from pyrolytic liquefaction of lignocellulosic biomass
Summary
A future bioeconomy relies on the efficient use of renewable resources for energy and material product supply. Bio-oils can be utilized in different ways, from heat generation (state-of-the-art today), as refinery feed after catalytic upgrading or for synthetic fuels production as developed within the b ioliq® process at the KIT (Karlsruhe Institute of Technology, Germany). At this plant, fast pyrolysis is evaluated in pilot scale [7, 8]. There, wheat straw as lowquality and ash-rich bioresource is mixed with hot sand and pyrolysis occurs at 500 °C within seconds This treatment yields products according to a mass balance: liquid [34% (w/w) bio-oil with 15% (w/w) water content, 25% (w/w) pyrolysis water (PW) with 80% (w/w) water content], solid [20% (w/w) char and ash], and pyrolysis gas [20% (w/w), non-condensable] [7]. We conceived a biotechnological approach for the valorization of PW in a growth-coupled biotransformation to manufacture 1,2-propanediol (1,2-PDO, propylene glycol) with Corynebacterium glutamicum
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