Optimization of media nutrient composition for increased photofermentative hydrogen production by Synechocystis sp. PCC 6803

By optimizing concentrations of key nutrients in the media of Synechocystis sp. PCC 6803, we achieved nearly 150-fold greater photofermentative hydrogen (H2) production than was achieved by analogous, sulfur-deprived cultures, which are well known to produce much more H2 than cultures grown on complete media. This was associated with a 44-fold increase in glycogen concentration. Using response surface methodology to determine optimum conditions, we found that, instead of completely starving cells of sulfur or another essential nutrient, the highest H2 production (0.81 ± 0.36 μmol H2 mg Chl−1 h−1) occurred with 0.52 mM NH4+, 20.1 μM SO42−, and 46 mM HCO3−. H2 profiling experiments provided initial screening of NH4+, HCO3−, SO42−, and PO43− concentrations and identified the significant variables in H2 production to be NH4+, SO42−, and the interactions of both NH4+ and SO42− with HCO3−. Our results indicate that optimized amounts of nitrogen and sulfur in the nutrient media are superior to total deprivation of these nutrients for H2 production.