Print Email Facebook Twitter Physiological and stoichiometric characterization of ethanol-based chain elongation in the absence of short-chain carboxylic acids Title Physiological and stoichiometric characterization of ethanol-based chain elongation in the absence of short-chain carboxylic acids Author Allaart, M.T. (TU Delft BT/Environmental Biotechnology) Fox, B.B. (TU Delft Reflection & Lifestyle) Nettersheim, I.H.M.S. (TU Delft BN/Marie-Eve Aubin-Tam Lab) Pabst, Martin (TU Delft BT/Environmental Biotechnology) Sousa, Diana Z. (Wageningen University & Research) Kleerebezem, R. (TU Delft BT/Environmental Biotechnology) Date 2023 Abstract Hexanoate is a valuable chemical that can be produced by microorganisms that convert short-chain- to medium-chain carboxylic acids through a process called chain elongation. These microorganisms usually produce mixtures of butyrate and hexanoate from ethanol and acetate, but direct conversion of ethanol to hexanoate is theoretically possible. Steering microbial communities to ethanol-only elongation to hexanoate circumvents the need for acetate addition and simplifies product separation. The biological feasibility of ethanol elongation to hexanoate was validated in batch bioreactor experiments with a Clostridium kluyveri-dominated enrichment culture incubated with ethanol, acetate and butyrate in different ratios. Frequent liquid sampling combined with high-resolution off-gas measurements allowed to monitor metabolic behavior. In experiments with an initial ethanol-to-acetate ratio of 6:1, acetate depletion occurred after ± 35 h of fermentation, which triggered a metabolic shift to direct conversion of ethanol to hexanoate despite the availability of butyrate (± 40 mCmol L−1). When only ethanol and no external electron acceptor was supplied, stable ethanol to hexanoate conversion could be maintained until 60–90 mCmol L−1 of hexanoate was produced. After this, transient production of either acetate and butyrate or butyrate and hexanoate was observed, requiring a putative reversal of the Rnf complex. This was not observed before acetate depletion or in presence of low concentrations (40–60 mCmol L−1) of butyrate, suggesting a stabilizing or regulatory role of butyrate or butyrate-related catabolic intermediates. This study sheds light on previously unknown versatility of chain elongating microbes and provides new avenues for optimizing (waste) bioconversion for hexanoate production. Subject OA-Fund TU Delft To reference this document use: http://resolver.tudelft.nl/uuid:3f35fb6b-1e33-40b7-88a0-2053e442bb7e DOI https://doi.org/10.1038/s41598-023-43682-x ISSN 2045-2322 Source Scientific Reports, 13 (1) Part of collection Institutional Repository Document type journal article Rights © 2023 M.T. Allaart, B.B. Fox, I.H.M.S. Nettersheim, Martin Pabst, Diana Z. Sousa, R. Kleerebezem Files PDF s41598_023_43682_x.pdf 1.5 MB Close viewer /islandora/object/uuid:3f35fb6b-1e33-40b7-88a0-2053e442bb7e/datastream/OBJ/view