Effect of co-cultivation of Chlamydomonas reinhardtii with Azotobacter chroococcum on hydrogen production

•Reducing the O2 content in the culture of C. reinhardtii is essential for its hydrogen production.•Co-cultivation of A. chroococcum and C. reinhardtii improved hydrogen yield of C. reinhardtii.•A. chroococcum promoted growth and starch content of the C. reinhardtii.•A. chroococcum decreased the respiratory rate and dissolved O2 of the C. reinhardtii.•A. chroococcum promoted activity of hydrogenase of the C. reinhardtii in co-culture medium.

Chlamydomonas reinhardtii cc124 and Azotobacter chroococcum bacteria were co-cultured with a series of volume ratios and under a variety of light densities to determine the optimal culture conditions and to investigate the mechanism by which co-cultivation improves H2 yield. The results demonstrated that the optimal culture conditions for the highest H2 production of the combined system were a 1:40 vol ratio of bacterial cultures to algal cultures under 200 μE m−2 s−1. Under these conditions, the maximal H2 yield was 255 μmol mg−1 Chl, which was approximately 15.9-fold of the control. The reasons for the improvement in H2 yield included decreased O2 content, enhanced algal growth, and increased H2ase activity and starch content of the combined system.