Screening for hydrogen-producing strains of green microalgae in phosphorus or sulphur deprived medium under nitrogen limitation

Hydrogen gas, one of the best candidates for clean and renewable energy, can be produced by microalgae that can use solar energy to cause photolysis of water. This study screened H₂-producing indigenous green microalgae under sulphur (S-) deprivation, simultaneous nitrogen (N-) limitation and S-deprivation, or simultaneous N-limitation and phosphorus (P-) deprivation. Sequences of 18S rDNA and ITS in conjunction with morphological characteristics were used to identify the algae. We report that Chlorella lewinii, Micractinium sp., Coelastrella sp., and Monoraphidium sp. have the ability to produce H₂. The increase in H₂ photoproduction when N is limited seems to be a universal phenomenon in most tested strains of Chlorella, in all strains of Chlamydomonas, but in no strain of Coelastrella, Micractinium, or Scenedesmus. Chlorella sorokiniana KU204 produced H₂ (46 ml/l) under S-deprivation. This strain exhibited the highest H₂-producing ability (1.30 ml l^-1 h^-1) and accumulated up to 90 ml/l under simultaneous N-limitation and S-deprivation. Interestingly, C. sorokiniana KU204 could also produce H₂ under simultaneous N-limitation and P-starvation (69 ml/l). The induction time to reach an anoxic state by most tested strains of Chlorella, but not Chlamydomonas, was shorter under simultaneous N-limitation and S-deprivation than under S-deprivation. In addition, those strains of Chlorella exhibited high H₂ photoproduction under simultaneous N-limitation and S-deprivation. A few Chlorella strains were unable to reach an anoxic state during the experiment. However, such regularity is not found in Chlamydomonas. The results indicate that the mechanism of H₂ photoproduction in Chlorella may differ from that in Chlamydomonas.