Effects of pH and acetic acid on glucose and xylose metabolism by a genetically engineered ethanologenic Escherichia coli

Journal Article · · Applied Biochemistry and Biotechnology; (United States)

DOI:https://doi.org/10.1007/BF02918999· OSTI ID:6468963

Lawford, H G; Rousseau, J D ^[1]

---

1. Univ. of Toronto, Ontario (Canada)

Efficient utilization of the pentosan fraction of hemicellulose from lignocellulosic feedstocks offers an opportunity to increase the yield and to reduce the cost of producing fuel ethanol. The patented, genetically engineered, ethanologen Escherichia coli B (pLOI297) exhibits high-performance characteristics with respect to both yield and productivity in xylose-rich lab media. In addition to producing monomer sugar residues, thermochemical processing of biomass is known to produce substances that are inhibitory to both yeast and bacteria. During prehydrolysis, acetic acid is formed as a consequence of the deacetylation of the acetylated pentosan. Investigations have shown that the acetic acid content of hemicellulose hydrolysates from a variety of biomass/waste materials was in the range 2-10 g/L (33-166 mM). Increasing the reducing sugar concentration by evaporation did not alter the acetic acid concentration. Acetic acid toxicity is pH dependent. By virtue of its ability to traverse the cell membrane freely, the undissociated (protonated) form of acetic acid (HAc) acts as a membrane protonophore and causes its inhibitory effect by bringing about the acidification of the cytoplasm. With recombinant E. coli B, the pH range for optimal growth with glucose and xylose was 6.4-6.8. However, the decrease in growth and fermentation efficiency at pH 7 is not significant. At pH 7, only 0.56% of acetic acid is undissociated, and at 10 g/L, neither the ethanol yield nor the maximum volumetric productivity, with glucose or xylose, is significantly decreased. The [open quotes]uncoupling[close quotes] effect of HAc is more pronounced with xylose and the potency of HAc is potentiated in a minimal salts medium. Controlling the pH at 7 provided an effective means of circumventing acetic acid toxicity without significant loss in fermentation performance of the recombinant biocatalyst. 69 refs., 11 figs., 2 tabs.

• OSTI ID: 6468963
• Journal Information: Applied Biochemistry and Biotechnology; (United States), Journal Name: Applied Biochemistry and Biotechnology; (United States) Vol. 39-40; ISSN ABIBDL; ISSN 0273-2289
• Country of Publication: United States
• Language: English

Related Subjects

09 BIOMASS FUELS
090900* -- Biomass Fuels-- Processing-- (1990-)
550700 -- Microbiology
59 BASIC BIOLOGICAL SCIENCES
ACETIC ACID
ALCOHOL FUELS
ALDEHYDES
BACTERIA
BIOCONVERSION
BIOLOGICAL PATHWAYS
CARBOHYDRATES
CARBOXYLIC ACIDS
ESCHERICHIA COLI
ETHANOL FUELS
FERMENTATION
FUELS
GLUCOSE
HEXOSES
MICROORGANISMS
MONOCARBOXYLIC ACIDS
MONOSACCHARIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
PENTOSES
PH VALUE
PRODUCTION
SACCHARIDES
SYNTHETIC FUELS
TOXICITY
XYLOSE