Ammonia and hydrogen production by immobilized cyanobacteria

Abstract

Heterocystous cyanobacteria Anabaena azollae (symbiotic) and Mastigocladus laminosus (thermophilic) were immobilized in polyvinyl or polyurethane foams and in alginate. Following immobilization there was a progressive colonization of the matrices when incubated under light in suitable growth media. Scanning electron microscopy studies of polyvinyl and polyurethane foam immobilized cells showed the development of a filamentous mucilage connected to the surface of the matrix. Immobilization led to an increase and/or to a stabilization of the rate of H 2 photoproduction. This increase occurred mainly via hydrogenase-mediated production. Immobilization also stabilized nitrogenase activity and increased initial rates of nitrogen fixation by both species of cyanobacteria. Photoproduction of ammonia was monitored in the presence of l-methionine- d,l-sulfoximine, an inhibitor of glutamine synthetase activity. High yields of ammonia production, up to 400 μmol and 100 μmol mg chlorophyll −1 per 24 h, were obtained in batch reactors from polyvinyl foam immobilized A. azollae and M. laminosus, respectively, whereas control free-living cultures produced less than 10 μmol ammonia under the same conditions. A similar yield increase was observed when the membrane permeability of alginate-immobilized A. azollae was increased by an acetone pretreatment. This suggests that the increase in ammonia production on immobilization in polyvinyl foam is at least partly related to changes in membrane permeability induced by the immobilization process itself as a consequence of cell-matrix interactions.