Pathways involved in the microaerobic utilization of glycerol and the synthesis of fermentation products in native and engineered E. coli. Genetic modifications supporting the metabolic engineering strategies employed in this work are illustrated by thicker lines (overexpression of E. coli gldA-dhaKLM and glpK-glpD and S. bovis ldh) or cross bars (disruption of pflB, pta, adhE, frdA, ldhA, mgsA and lldD). Broken lines illustrate multiple steps. Relevant reactions are represented by the names of the gene(s) coding for the corresponding enzymes (E. coli genes/enzymes unless otherwise specified in parenthesis): aceEF-lpdA, pyruvate dehydrogenase complex; adhE, acetaldehyde/alcohol dehydrogenase; ackA, acetate kinase; aldA, aldehyde dehydrogenase A; dhaKLM, dihydroxyacetone kinase; dld, respiratory D-lactate dehydrogenase; fdhF, formate dehydrogenase, part of fomate hydrogenlyase complex; FrdABCD, fumarate reductase; gldA, glycerol dehydrogenase; gloA, glyoxalase I; gloB, glyoxalase II; glpD, aerobic glycerol-3-phosphate dehydrogenase; glpK, glycerol kinase; hycB-I, hydrogenase 3, part of formate hydrogenlyase complex; ldh, fermentative L-lactate dehydrogenase (S. bovis); ldhA, fermentative D-lactate dehydrogenase; lldD, respiratory L-lactate dehydrogenase; mgsA, methylglyoxal synthase; pflB, pyruvate formate-lyase; pta, phosphate acetyltransferase; pykF, pyruvate kinase. Abbreviations: DHA, dihydroxyacetone; DHAP, DHA phosphate; G-3-P, glycerol-3-phosphate; PEP, phosphoenolpyruvate; Pi, inorganic phosphate; PYR, pyruvate; P/O, amount of ATP produced in the oxidative phosphorylation per pair of electrons transferred through the electron transport system; QH2, reduced quinones; S-LG, S-lactoylglutathione; *, glyoxalase III.