TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preparation (Disclosed): The recombinant photosynthetic microorganism is prepared by standard recombinant methods. Preferred Polypeptide: The polypeptide that catalyzes substrate to product conversion is branched-chain 2-keto acid decarboxylase. The branched-chain 2-ketoacid decarboxylase is chosen from Saccharomyces cerevisiae pyruvate decarboxylase (PDC) 1, Pichia stipitis PDC1, S.cerevisiae PDC5, S.cerevisiae PDC6, S.cerevisiae AR010 gene product, S.cerevisiae THI3 gene product, P.stipitis PDC 3-6 Kivd gene product, P.stipitis PDC2, Mycobacterium tuberculosis ketoglutarate dehydrogenase multienzyme complex (KDC), Lactococcus lactis alpha -KDC, and their variant or homolog. The heterologous nucleic acid sequence preferably encodes L.lactis alpha -KDC, P.stipitis PDC3-6 or its variant. The heterologous nucleic acid sequence encodes L.lactis alpha -KDC-S286Y, alpha -KDC-S286U, F381W gene product, or its variant. The heterologous nucleic acid sequence encodes alcohol dehydrogenase (ADH) or branched-chain ADH. The alcohol dehydrogenase is chosen from S.cerevisiae ADH1, ADH2, ADH3, ADH6, ADH7, GRE2, SFA1 and YPR1, P.stipitis ADH3, ADH6, ADH7 or GRE2, M.tuberculosis ADH1, ADH and ADHb, Escherichia coli yqhD gene product, Equus ferus subsp. caballus ADHE gene product, and their variant or homolog, preferably encodes S.cerevisiae ADH6 gene product. The heterologous nucleic acid sequence further encodes one or more gene products chosen from acetolactate synthase, ketol-acid reductoisomerase and dihydroxyacid dehydratase, preferably acetolactate synthase for producing isobutanol, 2-methyl-1-butanol, or 3-methyl-1-butanol. The heterologous nucleic acid sequence further encodes one or more gene products chosen from 2-isopropylmalate synthase, 3-isopropylmalate dehydratase and 3-isopropylmalate dehydrogenase (preferably 2-isopropylmalate synthase) for producing 3-methyl-1-butanol. The heterologous nucleic acid sequence further encodes one or more gene products chosen from homoserine dehydrogenase, homoserine kinase, threonine synthase and threonine ammonia-lyase for producing 2-methyl-1-butanol. Preferred Method: The culture medium provides inorganic carbon as substantially sole carbon source. The inorganic carbon in the culture medium is carbon dioxide. The process of recovering the branched-chain alcohol involves gas stripping, steam stripping or performing pervaporation. EXAMPLE - No suitable example given.