The mechanism of hydrogen photoproduction by several algae

Abstract

In order to come to a more firmly based conclusion on the mechanism of hydrogen photoproduction in green algae, we have compared two additional genera of green algae, i.e., Ankistrodesmus and Chlorella, with the previously tested Chlamydomonas and Scenedesmus. None of the algae tested required photosystem II for H2 photoproduction, since this reaction still occurred in the presence of 10(-5)M DCMU. Photophosphorylation was also not required since two potent inhibitors of this process, Cl-CCP and SAL, almost always stimulated H2 photoproduction. However, the effect of the inhibitors was found to vary with the species of alga and also with the age and growth conditions of the culture. The highest concentration of SAL tested (10(-2)M) always stimulated H2 photoproduction by photoheterotrophically grown cells, but often inhibited this reaction in autotrophically grown cells. When present, this inhibition by SAL was associated with gross pigment damage. The variation in the effect of Cl-CCP upon H2 photoproduction due to different growth conditions was particularly striking for Chlorella vulgaris.Cl-CCP gave very little if any stimulation of this reaction in autotrophically grown cells of this alga, but stimulated H2 photoproduction by photoheterotrophically grown cells approximately 450%. Chlamydomonas cells were found to be about ten times as sensitive as the other cells to both poisons. We conclude that all of the algae tested are able to photoproduce H2 via non-cyclic electron flow through photosystem I to hydrogenase.

Photosystem I Is Indispensable for Photoautotrophic Growth, CO2 Fixation, and H2 Photoproduction inChlamydomonas reinhardtii

“…The respiration rate, as measured by uptake of 18 O 2 , was not greatly affected by the light (Table I). Under anaerobic conditions, the chloroplast enzyme hydrogenase is induced and can serve as an alternate acceptor of electrons from ferredoxin (31)(32)(33). After removal of O 2 , production of H 2 in WT cells was observed immediately upon illumination (Fig.…”

Pyruvate:Ferredoxin Oxidoreductase Is Coupled to Light-independent Hydrogen Production in Chlamydomonas reinhardtii

“…H 2 is generated by a highly efficient hydrogenase of the [Fe-Fe] type, HYDA1 (6 -8), which, despite its extreme sensitivity toward O 2 (9 -11), is located in the chloroplast (6). The natural electron donor of HYDA1 is the photosynthetic ferredoxin PETF (7,12), and the highest rates of H 2 evolution are observed in the light (4,13). However, the cells have to be adapted to dark anaerobic conditions to induce hydrogenase activity (7,14).…”

Isolation, characterization and N‐terminal amino acid sequence of hydrogenase from the green alga Chlamydomonas reinhardtii

“…Electrons can be supplied by photochemical water splitting at photosystem 11, which results in simultaneous production of hydrogen and oxygen [31, 321, or by metabolic oxidation of organic compounds under the release of carbon dioxide [33 -351. This process, strongly stimulated by glucose, is DCMUf3-(3,4-dichlorophenyl)-l,l -dimethylurea1 insensitive, requiring only photosystem-I activity [36]. Ferredoxin is the in vivo electron mediator in hydrogenase reactions in algae.…”