NOVELTY - A recombinant microbial host cell comprising at least one DNA molecule, is new. The DNA molecule is capable of encoding a polypeptide that catalyzes a substrate to product conversion chosen from (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxyisovalerate, (c) 2,3-dihydroxyisovalerate to alpha -ketoisovalerate, (d) alpha -ketoisovalerate to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol.    USE - The recombinant microbial host cell is useful for producing isobutanol (claimed) used as biofuel or fuel additive, and industrial commodity chemical.    ADVANTAGE - The host cell produces isobutanol cost-effectively as a single product, and is environmentally-friendly, and avoids negative environmental impact associated with petrochemical isobutanol processes. The isobutanol has energy content similar to gasoline and can be blended with any fossil fuel, is favored as fuel or fuel additive as the isobutanol yields only carbon dioxide and fewer amount of sulfur oxide or nitrous oxide or no sulfur oxide or nitrous oxide when burned in standard internal combustion engine, overcomes hydrogen distribution problems in emerging fuel industry, and can be easily reformed for its hydrogen content and can be distributed through gas stations in the purity required for fuel cells or vehicles.    DETAILED DESCRIPTION - A recombinant microbial host cell comprising at least one DNA molecule, is new. The DNA molecule is capable of encoding a polypeptide that catalyzes a substrate to product conversion chosen from (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxyisovalerate, (c) 2,3-dihydroxyisovalerate to alpha -ketoisovalerate, (d) (i) alpha -ketoisovalerate to isobutyraldehyde, (ii) alpha -ketoisovalerate to isobutyryl-coenzymeA , and isobutyryl-coenzymeA to isobutyraldehyde, or (iii) alpha -ketoisovalerate to valine, valine to isobutylamine, and isobutylamine to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol, where the DNA molecule is heterologous to the microbial host cell, and the microbial host cell produces isobutanol. An INDEPENDENT CLAIM is included for method for producing isobutanol, which involves (a) providing the above-cited recombinant microbial host cell, and (b) contacting the host cell with (i) a fermentable carbon substrate in a fermentation medium under conditions for producing isobutanol, or (ii) a fermentable carbon in a fermentation medium substrate under conditions for producing isobutanol.