Two-stage photo-biological production of hydrogen by marine green alga Platymonas subcordiformis

Abstract A marine green alga, Platymonas subcordiformis , was demonstrated to photobiologically evolve hydrogen (H 2 ) after the first stage of photosynthesis, when subjected to a two-phase incubation protocol in a second stage of H 2 production: anaerobic incubation in the dark followed by the exposure to light illumination. The anaerobic incubation induced hydrogenase activity to catalyse H 2 evolution in the following phase of light illumination. H 2 evolution strongly depended upon the duration of anaerobic incubation, deprivation of sulphur (S) from the medium and the medium pH. An optimal anaerobic incubation period of 32 h gave the maximum H 2 evolution in the second phase in the absence of sulphur. Evolution of H 2 was greatly enhanced by 13 times when S was deprived from the medium. This result suggests that S plays a critical role in the mediation of H 2 evolution from P. subcordiformis . A 14-fold increase in H 2 production was obtained when the medium pH increased from 5 to 8; with a sharp decline at pH above eight. H 2 evolution was enhanced by 30–50% when supplementing the optimal concentrations of 25 mM acetate and 37.5 mM glucose.