Enhanced hydrogen production by a marine photosynthetic bacterium, Rhodobacter marinus, immobilized onto light-diffusing optical fibers

The marine photosynthetic bacterium Rhodobacter marinus strain NKPB0021 was isolated previously and shown to produce hydrogen at high levels. In order to enhance hydrogen photoproduction by this bacterium, we have immobilized cells directly onto the surface of optical fibers using alginate gel. The optical fibers emit light laterally from their surface and were used to construct a photobioreactor for efficient distribution of light to the cells. Hydrogen production by this reactor was determined using free cell suspensions and cells immobilized directly onto the optical fibers. Enhanced photoproduction of hydrogen was obtained in the latter case. An optimum hydrogen production rate of 16.9 μmol/mg (gel)/h was obtained using a cell concentration in the gel of 4.5 mg dry wt/ml and at a light intensity of 135 μE/m²/s at the fiber surface. In addition, improved mechanical stability and resistance to oxygen was obtained by coating the immobilized cells with a transparent layer of gellan gum. This immobilization procedure can be used as a general method for improving the light supply for photobiological processes.