TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The enzyme that catalyzes reaction: (a) is an acetolactate synthase; (b) is a ketol-acid reductoisomerase; (c) is a dihydroxy-acid dehydratase; (d) is a branched-chain ketoacid dehydrogenase; (e) is an isobutyryl-CoA mutase; and/or (f) and (g) is an acyl-CoA reductase and an alcohol dehydrogenase respectively, or a bifunctional acetaldehyde/alcohol dehydrogenase. The microbial cell: is a bacterium (Bacillus, Geobacillus, Brevibacillus, Lactobacillus, Lactococcus, Corynebacterium, Escherichia, Pseudomonas, Streptomyces, Propionibacterium or Clostridium), a filamentous fungus (Aspergillus, Penicillium or Trichoderma), a yeast (Saccharomyces, Kluyveromyces or Pichia) or an alga; and is preferably Bacillus subtilis.    TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation: No preparation method is given.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: The step of fermenting the microbial cell is carried out under anaerobic conditions, where butanol is recovered from the fermentation broth. EXAMPLE - The P15-icmAB expression cassette comprising a nucleotide sequence of SEQ ID NO: 23 (Sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication) was synthesized according to a DNA whole synthesis method of Cello et al. 2002, Science 297:1016-8. The Streptomyces cinnamonensis icmA and icmB genes were codon pair-optimized for optimal expression in Bacillus subtilis using the design procedures described in patent WO2008/000362 (excluding Shine Delgarno, BamHI, EcoRI and HindIII sites). The resulting DNA cassette was cloned between the BamHI and HindIII sites of the pDG364 B. subtilis integration vector to produce the plasmid pBT1. The P15-icmAB-carrying plasmid was then transformed into strain 1A747 using standard chloramphenicol selection to integrate a single-copy of the P15-icmAB cassette into the non-essential amyE locus. One chloramphenicol resistant colony was selected and renamed B. subtilis BSBT1. The pxyl-adhE overexpressing cassette comprising the nucleotide sequence of SEQ ID NO: 24 (Sequences not defined here may be found at ftp://ftp.wipo.int/pub/published_pct_sequences/publication) was prepared by in vitro DNA synthesis methods. The cassette was inserted between the SpeI and BamHI sites of the B. subtilis integration vector pAX01 to produce the plasmid pBT20. The adhE gene was codon-pair optimized for optimal expression in B. subtilis using the same procedure as for the icmA and icmB genes. The pxyl-adhE-carrying plasmid was transformed into the P15-icmAB/amyE-containing strain BSBT1. Transformed erythromycin resistant colonies were selected by standard method. One selected erythromycin resistant colony was named B. subtilis BSBT11. This strain contained a single-copy of the P15-icmAB cassette integrated at the amyE locus and a single-copy of the pxyl-adhE cassette integrated at the lac4 locus. The strain BSBT11 was grown overnight at 37 degrees C anaerobically under static conditions to produce butanol (0.8 mu g/ml).