Effect of organic acids on the growth and fermentation of ethanologenic Escherichia coli LY01

Abstract

Hemicellulose residues can be hydrolyzed into a sugar syrup using dilute mineral acids. Although this syrup represents a potential feedstock for biofuel production, toxic compounds generated during hydrolysis limit microbial metabolism. Escherichia coli LY01, an ethanologenic biocatalyst engineered to ferment the mixed sugars in hemicellulose syrups, has been tested for resistance to selected organic acids that are present in hemicellulose hydrolysates. Compounds tested include aromatic acids derived from lignin (ferulic, gallic, 4-hydroxybenzoic, syringic, and vanillic acids), acetic acid from the hydrolysis of acetylxylan, and others derived from sugar destruction (furoic, formic, levulinic, and caproic acids). Toxicity was related to hydrophobicity. Combinations of acids were roughly additive as inhibitors of cell growth. When tested at concentrations that inhibited growth by 80%, none appeared to strongly inhibit glycolysis and energy generation, or to disrupt membrane integrity. Toxicity was not markedly affected by inoculum size or incubation temperature. The toxicity of all acids except gallic acid was reduced by an increase in initial pH (from pH 6.0 to pH 7.0 to pH 8.0). Together, these results are consistent with the hypothesis that both aliphatic and mononuclear organic acids inhibit growth and ethanol production in LY01 by collapsing ion gradients and increasing internal anion concentrations.

Cellulosic ethanol production from AFEX-treated corn stover using Saccharomyces cerevisiae 424A(LNH-ST)

“…An equally important benefit of the degradation products from AFEX-pretreated biomass is that they increase metabolism of sugars which translates into higher specific ethanol production rates. Degradation compounds such as organic acids and 4-hydroxybenzaldehye have been shown to stimulate fermentation when present at moderate levels (22,23). Nonetheless, they inhibit the cells from propagating to a density warranted by available nutrients.…”

Metabolite stress and tolerance in the production of biofuels and chemicals: Gene‐expression‐based systems analysis of butanol, butyrate, and acetate stresses in the anaerobe Clostridium acetobutylicum

“…Mechanisms of solvent and carboxylic acid toxicity/stress have been studied mostly in Gram-negative (Gram À ) organisms and notably in Escherichia coli (Arnold et al, 2001;Chang and Cronan, 1999;Hayashi et al, 2003;Isken and de Bont, 1998;Kirkpatrick et al, 2001;Roe et al, 2002;Russell and Diez-Gonzalez, 1998;Sardessai and Bhosle, 2002;Zaldivar and Ingram, 1999). For example, Gram À organisms have evolved adaptive mechanisms to tolerate solvents, including alterations in cell membrane, active secretion, and activation of general stress response (Isken and de Bont, 1998;Sardessai and Bhosle, 2002).…”

Molecular characterization of the phenolic acid metabolism in the lactic acid bacteria Lactobacillus plantarum

“…Under their free form, phenolic acids are considered differently according to the microorganisms. Phenolic acids have inhibitory effect on the growth of most microorganisms [4,34]. It is the reason why they are used as antimicrobial agents in the food industry [25].…”