Response of green alga Tetraspora sp. CU2551 under potassium deprivation: a new promising strategy for hydrogen production

With increasing world energy consumption, renewable energy sources can fulfill the need and many have net zero carbon dioxide emissions. One of these is hydrogen, which is biologically produced molecular hydrogen from organisms. Although many studies have produced hydrogen from green algae and optimized conditions to obtain the highest yield, following our previous works on production optimization from Tetraspora sp. CU2551, we tested deprivation of Fe, Cu, Ca, S, Mg, or K, and surprisingly found that K deprivation showed another promising switch in increased H 2 yield, representing 9.2 ± 0.1 μmol mg −1 DW within 32 h incubation anaerobically. Moreover, longer cell adaptation by aerobic incubation, before production phase, resulted in higher hydrogen yield. Cells adapted in potassium deprivation (TAP-K medium) promoted hydrogen production to a yield of 14.8 ± 0.03 μmol mg −1 DW, or about 3.0 times higher than normal TAP (5.0 ± 0.82 μmol mg −1 DW). The increased yield was caused by (1) lowering PSII activity (direct biophotolysis), resulted in less oxygen being produced, lowering hydrogenase inhibitor levels, and (2) increasing accumulated starch degradation (indirect biophotolysis) (12.2% starch remaining or 7.2 ± 0.9 μg mg −1 DW), increased the flow of electrons to hydrogenase. Our finding makes potassium deprivation conditions as another the promising choice to enhance hydrogen production in biological systems.