NOVELTY - Producing a carbon-based product involves: preparing a heterologous DNA sequence operably linked to an expression vector; transforming a thermophilic cyanobacterium host with the vector; and culturing the host.    USE - For producing a carbon-based product selected from ethyl ester, methyl ester, sucrose, alcohol, ethanol, propanol, isopropanol, butanol, fatty alcohols, fatty acid ester, wax ester, hydrocarbons, n-alkanes, propane, octane, diesel, Jet propellant 8 (JP8), polymers, terephthalate, polyol, 1,3-propanediol, 1,4-butanediol, polyhydroxyalkanoates (PHA), poly- beta -hydroxybutyrate (PHB), acrylate, adipic acid, epsilon -caprolactone, isoprene, caprolactam, rubber, lactate, docosahexaenoic acid (DHA), 3-hydroxypropionate, gamma -valerolactone, lysine, serine, aspartate, aspartic acid, sorbitol, ascorbate, ascorbic acid, isopentenol, lanosterol, omega -3 DHA, lycopene, itaconate, 1,3-butadiene, ethylene, propylene, succinate, citrate, citric acid, glutamate, malate, 3-hydroxypropionic acid (HPA), lactic acid, teterahydrofuran (THF), gamma butyrolactone, pyrrolidones, hydroxybutyrate, glutamic acid, levulinic acid, acrylic acid, malonic acid, carotenoid, isoprenoid, itaconic acid, limonene, pharmaceutical or pharmaceutical intermediates, erythromycin 7-aminodeacetoxycephalosporanic acid (7-ADCA)/cephalosporin, polyketides, statin, paclitaxel, docetaxel, terpene, peptide, steroid, and an omega fatty acid (preferably alcohol, especially ethanol), and for producing a fuel composition, and acetaldehyde (claimed), where ethanol is used as a solvent, antiseptic, rocket propellant, renewable fuel source and as a base compound for the manufacture of other industrially important organic compounds.    ADVANTAGE - The cyanobacterium produces at least 1000, at least 5000, at least 10000, at least 12000, or at least 15000 mg ethanol per liter of culture medium (preferably the cyanobacterium produces 1000-20000 mg ethanol per liter of culture medium). The cyanobacterium further produces acetaldehyde and where the ratio of ethanol to acetaldehyde is at least 500 (preferably at least 4500, especially 4000-15000, or 500-3000). The method enables host cell to achieve increased transformation efficiency and, thus, is optimized for use in a genetic system for production of various carbon-based products. The method increases the efficiency of the process where an organism is optimized for use in a genetic system for clean and efficient ethanol production.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: 1) a modified thermosynechococcus cell comprising a recombinant marker gene and gamma phage cI promoter where the marker gene is operably linked to the promoter; 2) an isolated or recombinant polynucleotide comprising a nucleic acid sequence selected from: any one of the sequences from Table 3 as given in the specification; a nucleic acid sequence at least 80 (preferably at least 99.9)% identical to any one of the sequences from Table 3 as given in the specification; and a nucleic acid sequence that hybridizes under stringent conditions to any one of the sequences in Table 3 as given in the specification; 3) a modified Thermosynechococcus cell comprising an alcohol dehydrogenase gene and a pyruvate decarboxylase gene; 4) producing a carbon-based product involving culturing the cell where the cell produces the carbon-based product; and 5) engineering a thermophilic cyanobacterium involving transforming the thermophilic cyanobacterium with a heterologous DNA sequence operably linked to an expression vector.