synthesis |
Ralstonia eutropha H16 produces polyhydroxybutanoate as an intracellular carbon storage material. The excess carbon can be redirected in engineered strains from polyhydroxybutanoate storage to the production of isobutanol and 3-methyl-1-butanol (branched-chain higher alcohols). Strains of Ralstonia eutropha with isobutyraldehyde dehydrogenase activity, in combination with the overexpression of plasmid-borne, native branched-chain amino acid biosynthesis pathway genes and the overexpression of heterologous ketoisovalerate decarboxylase gene, are employed for the biosynthesis of isobutanol and 3-methyl-1-butanol. One mutant strain produces over 180 mg/l branched-chain alcohols in flask culture, and is significantly more tolerant of isobutanol toxicity than wild-type. After the elimination of genes ilvE, bkdAB, and aceE, the production titer improves to 270 mg/l isobutanol and 40 mg/l 3-methyl-1-butanol. Under semicontinuous flask cultivation, the strain grows and produces more than 14 g/l branched-chain alcohols over the duration of 50 days |
Lactococcus lactis subsp. lactis |