NOVELTY - A recombinant microbial host cell comprising at least one DNA molecule encoding a polypeptide capable of catalyzing a substrate to product conversion chosen from (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxy-isovalerate, (c) 2,3-dihydroxy-isovalerate to alpha -ketoisovalerate, (d) alpha -ketoisovalerate to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol, is new.    USE - The recombinant microbial host cell chosen from bacterium, Cyanobacterium, filamentous fungus and yeast is useful for producing isobutanol. The cell is a member of genus chosen from Clostridium, Zymomonas, Escherichia, Salmonella, Rhodococcus, Pseudomonas, Bacillus, Lactobacillus, Enterococcus, Alcaligenes, Klebsiella, Paenibacillus, Arthrobacter, Corynebacterium, Brevibacterium, Pichia, Candida, Hansenula and Saccharomyces. The cell is Escherichia coli, Alcaligenes eutrophus, Bacillus licheniformis, Paenibacillus macerans, Rhodococcus erythropolis, Pseudomonas putida, Bacillus subtilis, Lactobacillus plantarum, Enterococcus faecium, Enterococcus gallinarum, Enterococcus faecalis and Saccharomyces cerevisiae (all claimed). The isobutanol is used as biofuel or fuel additive.    ADVANTAGE - The recombinant microbial host cell enables environmentally-friendly and cost-effective production of isobutanol.    DETAILED DESCRIPTION - A recombinant microbial host cell comprising at least one DNA molecule encoding a polypeptide capable of catalyzing a substrate to product conversion chosen from (i) (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxy-isovalerate, (c) 2,3-dihydroxy-isovalerate to alpha -ketoisovalerate, (d) alpha -ketoisovalerate to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol, or (ii) (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxy-isovalerate, (c) 2,3-dihydroxy-isovalerate to alpha -ketoisovalerate, (f) alpha -ketoisovalerate to isobutyryl-CoA, (g) isobutyryl-CoA to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol, or (iii) (a) pyruvate to acetolactate, (b) acetolactate to 2,3-dihydroxy-isovalerate, (c) 2,3-dihydroxy-isovalerate to alpha -ketoisovalerate, (h) alpha -ketoisovalerate to valine, (i) valine to isobutylamine, (j) isobutylamine to isobutyraldehyde, and (e) isobutyraldehyde to isobutanol, is new. The DNA molecule is heterologous to the microbial host cell, where the microbial host cell produces isobutanol. An INDEPENDENT CLAIM is included for method for producing isobutanol, which involves (a) providing the above-mentioned recombinant microbial host cell containing at least one DNA molecule encoding a polypeptide capable of catalyzing substrate to product conversion chosen from the above-cited pathways (i-ii), and (b) contacting the host cell with fermentable carbon substrate in fermentation medium under conditions to produce isobutanol.