In the context of hydrogen production by the green alga Chlamydomonas reinhardtii, the control of light attenuation conditions is used to set-up anoxia under illuminated and autotrophic conditions, without affecting photosynthetic capacities of cells (as with sulphur deprivation or PSII inhibitors like DCMU). This paper presents a full description of the protocol where the incident photons flux density (PFD) is adapted during cultivation in order to obtain a sufficiently low illuminated fraction γ under 0.25 leading to anoxic hydrogen producing conditions during several days. The protocol is validated in a torus-shape photobioreactor (PBR) revealing after few days of anoxic conditions a peak of hydrogen production (1.44 ml H2/h/l of culture; [0.8-1.0] ml H2/h/g of dry weight biomass) concomitant with a decrease of biomass concentration, protein content and maximal photosynthetic yield. Effect of over-accumulating starch, as being known to increase hydrogen production by the PSII-independent pathway, is also investigated.
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