Physiological and stoichiometric characterization of ethanol-based chain elongation in the absence of short-chain carboxylic acids

MT Allaart, BB Fox, IHMS Nettersheim, M Pabst… - Scientific Reports, 2023 - nature.com
Scientific Reports, 2023nature.com
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 …
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.
nature.com
以上显示的是最相近的搜索结果。 查看全部搜索结果