title: Acetate accumulation enhances mixed culture fermentation of biomass to lactic acid.
abstract: Lactic acid is a high-in-demand chemical, which can be produced through fermentation of lignocellulosic feedstock. However, fermentation of complex substrate produces a mixture of products at efficiencies too low to justify a production process. We hypothesized that the background acetic acid concentration plays a critical role in lactic acid yield; therefore, its retention via selective extraction of lactic acid or its addition would improve overall lactic acid production and eliminate net production of acetic acid. To test this hypothesis, we added 10 g/L of acetate to fermentation broth to investigate its effect on products composition and concentration and bacterial community evolution using several substrate-inoculum combinations. With rumen fluid inoculum, lactate concentrations increased by 80 ± 12 % (cornstarch, p < 0.05) and 16.7 ± 0.4 % (extruded grass, p < 0.05) while with pure culture inoculum (Lactobacillus delbrueckii and genetically modified (GM) Escherichia coli), a 4 to 23 % increase was observed. Using rumen fluid inoculum, the bacterial community was enriched within 8 days to >69 % lactic acid bacteria (LAB), predominantly Lactobacillaceae. Higher acetate concentration promoted a more diverse LAB population, especially on non-inoculated bottles. In subsequent tests, acetate was added in a semi-continuous percolation system with grass as substrate. These tests confirmed our findings producing lactate at concentrations 26 ± 5 % (p < 0.05) higher than the control reactor over 20 days operation. Overall, our work shows that recirculating acetate has the potential to boost lactic acid production from waste biomass to levels more attractive for application.
authors.affiliation: Department of Biochemical and Microbial Technology, Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Way Cern
authors.initials: WC
authors.lastname: Khor
authors.affiliation: Department of Biochemical and Microbial Technology, Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Hugo
authors.initials: H
authors.lastname: Roume
authors.affiliation: Department of Biochemical and Microbial Technology, Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.|Centre for Sustainable Chemical Technologies (CSCT), University of Bath, Claverton Down, Bath, BA2 7AY, UK.
authors.forename: Marta
authors.initials: M
authors.lastname: Coma
authors.affiliation: Department of Biochemical and Microbial Technology, Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium.
authors.forename: Han
authors.initials: H
authors.lastname: Vervaeren
authors.affiliation: Department of Biochemical and Microbial Technology, Centre for Microbial Ecology and Technology (CMET), Ghent University, Coupure Links 653, 9000, Ghent, Belgium. Korneel.Rabaey@UGent.be.
authors.forename: Korneel
authors.initials: K
authors.lastname: Rabaey
mesh_terms: D000085:Acetates / Q000378:metabolism*; D000818:Animals; D018533:Biomass; D001711:Biotransformation; D005285:Fermentation; D019344:Lactic Acid / Q000378:metabolism*; D008031:Lignin / Q000378:metabolism*; D059013:Microbial Consortia; D012417:Rumen / Q000382:microbiology*
chemical_list: D000085:Acetates; C036909:lignocellulose; D019344:Lactic Acid; D008031:Lignin
keywords: Acetate; Lactic acid; Lignocellulosic biomass; Mixed culture