Co-cultivation of Bradyrhizobium japonicum with Chlamydomonas reinhardtii strain cc849 or the transgenic strain lba, which was hetero-expressed the gene of the soybean leghemoglobin apoprotein Lba in chloroplasts of the strain cc849, in Tris-acetate-phosphate (TAP) or TAP-sulfur free media, improved H-2 yield. H-2 production was 14 times and growth was 26% higher when strain lba and B. japonicum were co-cultured, as compared with cultivation of the algal strain alone under the same conditions. The increase in respiration rate or fast O-2 consumption by about 8 times in the co-cultures was the major reason for the improvement. (C) 2012 Elsevier Ltd. All rights reserved.