NOVELTY - A cyanobacterial cell comprises a Photosystem I (PSI) complex which accepts electrons from at least one respiratory cytochrome.    USE - In bioreactor for producing hydrogen gas (claimed).    ADVANTAGE - The thermophilic cyanobacteria are genetically engineered to separate Photosystem I (PSI) and Photosystem II (PSII) for hydrogen production, such that Photosystem II (PSII) becomes temperature sensitive (i.e. not operative in the non-permissive temperature of 60 degrees C, but operative at permissive temperatures of 50 degrees C), Thus in the non-permissive temperatures when PSII is disabled (and oxygen production inhibited) the cytochromes donate the electrons to PSI and hydrogen is produced unhampered by the debilitating effects of oxygen on the hydrogenase. These periods is alternated with the permissive temperature periods in which recovery of PSII will occur and regular growth and propagation of the cyanobacteria will proceed.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for following:    (1) new an isolated polynucleotide encoding a polypeptide which comprising a Photosystem I reaction centre subunit IX (PsaJ) amino acid sequence attached to a Photosystem I reaction centre subunit III precursor (PsaF) amino acid sequence which when expressed in a cyanobacteria accepts electrons from at least one respiratory cytochrome;    (2) new nucleic acid construct comprising the isolated polynucleotide;    (3) new isolated polypeptide as set forth in SEQ ID NO: 1 (SEQ ID NO: Not defined);    (4) a bioreactor for producing hydrogen comprising a tubing for holding cells, where a first section of tubing is placed in a first containment being maintained at a temperature of 60-70 degrees C and a second section of tubing is placed in a second containment is maintained at a temperature of 30-50 degrees C; and a recirculation pump configured such that cells circulate through tubing;    (5) producing hydrogen gas involving culturing the cyanobacterial cell under conditions that generate hydrogen gas in the cyanobacterial cell, by producing hydrogen gas.