Biological viability of Chlamydomonas reinhardtii cells entrapped in alginate beads for ammonium photoproduction

The green alga Chlamydomonas reinhardtii was immobilized by entrapment in Ca2+-alginate gel for ammonium photoproduction. The physical characteristics of the beads, their stability and ammonium-photoproduction capacity were affected by a variety of interactive factors, including cell loading, alginate viscosity and concentration, and the nature of the buffered medium. Electron micrographs show alterations in the morphology of the immobilized cells. Entrapped C. reinhardtii cells retained their biological viability, maintaining normal photosynthetic and respiratory activities, and they grew inside the gel beads, with a generation time of 9 h as compared with the 8 h shown by free cells under similar conditions. The unusually high rates for nitrite uptake and ammonium photoproduction, as well as the nitrite reductase activity shown by alginate-immobilized cells, were related to the changes in the membrane permeability induced by cell-matrix interaction.