Extended H2 photoproduction by N2-fixing cyanobacteria immobilized in thin alginate films

Screening of the University of Helsinki Culture Collection for naturally good H2 producing cyanobacteria recently revealed several promising strains. One of the superior strains is Calothrix 336/3, an N2-fixing heterocystous filamentous cyanobacterium. Making use of an important feature of the Calothrix 336/3 cells to adhere to the substrate, we applied an immobilization technique to improve H2 production capacity of this strain. We examined the basic properties of immobilization in Ca2+-alginate films in response to the production of H2 of the Calothrix 336/3 strain and as reference strains we used a model organism Anabaena PCC 7120 and its uptake hydrogenase mutant, ΔhupL, that allow us to compare the responses of different strains to alginate entrapment. Immobilization of the Calothrix 336/3 and ΔhupL mutant cells in Ca2+-alginate resulted in prolonged H2 production over several cycles. Immobilization of the Calothrix 336/3 cells was most successful and production of H2 could be measured even after 40 days after immobilization.

► The Calothrix 336/3 cells entrapped in Ca2+-alginate films produce substantially more H2 at much longer time course.
► Immobilization in Ca2+-alginate films stabilizes the filamentous cells, has a positive effect on cell viability, and reduces the growth of cells.
► CO2 is an important determinant for efficient H2 production in immobilized Calothrix 336/3 cultures.