NOVELTY - Method (M1) for producing carbon-based product of interest, involves culturing an engineered cyanobacterial cell in a cell culture in the presence of carbon dioxide and light under conditions suitable to produce a carbon-based product of interest, where the engineered cyanobacterial cell comprises a recombinant nucleic acid encoding an enzyme classified under an enzyme commission number chosen from EC 1.11.1.6, EC 1.11.1.7, and EC 1.11.1.21.    USE - The method is useful for producing carbon-based product of interest, preferably ethanol (claimed). The carbon-based product of interest includes alcohols e.g. ethanol, propanol, isopropanol and butanol, hydrocarbons and alkanes e.g. propane, octane and diesel, polymers e.g. terephthalate, polyhydroxyalkanoates and rubber, commodity chemicals e.g. lactate, docosahexaenoic acid, specialty chemicals e.g. carotenoids and isoprenoids, pharmaceuticals and pharmaceutical intermediates e.g. erythromycin, polyketides, peptides and steroids and bio fuels used for producing e.g. nutritional supplements, neutraceuticals, paraffin replacements and personal care products.    ADVANTAGE - The method produces ethanol with a production rate of greater than a rate chosen from 50 mg/L/day, 100 mg/L/day, 150 mg/L/day, 200 mg/L/day, 250 mg/L/day, 300 mg/L/day, 350 mg/L/day, and 400 mg/L/day, or greater than a rate chosen from 13 mg/L/hour, 14 mg/L/hour, 15 mg/L/hour, and 16 mg/L/hour, improves yield, reduces contamination that inhibits production of hydrocarbons by recombinant photosynthetic microorganisms, and utilizes recombinant photosynthetic microorganism engineered to maximize viability.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following: (1) method (M2) for conferring hydrogen peroxide resistance to a parent cyanobacterial cell, involves (a) transforming the parent cyanobacterial cell with a nucleic acid encoding an enzyme chosen from Mycobacterium tuberculosis catalase-peroxidase (KatG) and M.avium catalase HPII (KatE) resulting in an engineered cyanobacterial cell, and (b) culturing the engineered cyanobacterial cell in a medium comprising hydrogen peroxide; and (2) engineered host cell comprising a recombinant gene encoding the above-mentioned first enzyme, where the host cell further comprises a recombinant pyruvate decarboxylase or a recombinant alcohol dehydrogenase.