Effect of selected aldehydes on the growth and fermentation of ethanologenicEscherichia coli

TLDR

Bioethanol production from lignocellulosic raw materials requires hydrolysis of carbohydrate polymers into a fermentable syrup, during which dilute‑acid hemicellulose hydrolysis generates toxic compounds such as soluble aromatic aldehydes from lignin and furfural from pentose degradation. The study investigated the toxicity of representative aldehydes (furfural, HMF, 4‑hydroxybenzaldehyde, syringaldehyde, vanillin) as inhibitors of growth and ethanol production by ethanologenic E. coli B derivatives KO11 and LY01. The authors assessed growth and ethanol production inhibition by exposing the strains to these aldehydes, measuring toxicity on a weight basis and evaluating additive effects in binary combinations. Aromatic aldehydes were at least twice as toxic as furfural or HMF, with additive toxicities in binary mixtures except when combined with furfural, which was unexpectedly more toxic; their potency correlated with hydrophobicity but did not cause membrane damage, and only furfural strongly inhibited ethanol production, while the LY01 strain proved as resistant or more resistant than other biocatalysts.

Abstract

Bioethanol production from lignocellulosic raw-materials requires the hydrolysis of carbohydrate polymers into a fermentable syrup. During the hydrolysis of hemicellulose with dilute acid, a variety of toxic compounds are produced such as soluble aromatic aldehydes from lignin and furfural from pentose destruction. In this study, we have investigated the toxicity of representative aldehydes (furfural, 5-hydroxymethlyfurfural, 4-hydroxybenzaldehyde, syringaldehyde, and vanillin) as inhibitors of growth and ethanol production by ethanologenic derivatives of Escherichia coli B (strains KO11 and LY01). Aromatic aldehydes were at least twice as toxic as furfural or 5-hydroxymethylfurfural on a weight basis. The toxicities of all aldehydes (and ethanol) except furfural were additive when tested in binary combinations. In all cases, combinations with furfural were unexpectedly toxic. Although the potency of these aldehydes was directly related to hydrophobicity indicating a hydrophobic site of action, none caused sufficient membrane damage to allow the leakage of intracellular magnesium even when present at sixfold the concentrations required for growth inhibition. Of the aldehydes tested, only furfural strongly inhibited ethanol production in vitro. A comparison with published results for other microorganisms indicates that LY01 is equivalent or more resistant than other biocatalysts to the aldehydes examined in this study. © 1999 John Wiley & Sons, Inc. Biotechnol Bioeng 65: 24–33, 1999.