Sustained H₂ production in a Chlamydomonas reinhardtii D1 protein mutant

Abstract

In the present investigation, a detailed biochemical analysis of the high H₂ producer D1 protein mutant strain L159I-N230Y of Chlamydomonas reinhardtii, carrying a double amino acid substitution, was made. The leucine residue L159 was replaced by isoleucine, and the N230 asparagine was replaced by tyrosine. The performance of this strain was compared to that of the cc124 strain. The mutant showed a sustained capacity to donate electrons by means of direct biophotolysis for H₂ production, as demonstrated by the higher efficiency of utilization of the hydrogenase enzyme when carried out under anaerobic conditions. The latter property was maintained also under sulfur deprivation. Furthermore, when compared to the cc124, the mutant showed a higher amount of D1 protein content, a higher carbohydrate storage capacity and a sustained PSII direct contribution to the H₂ production during sulfur deprivation. The addition of DCMU to the cells showed that as much as 7.0 mL H₂ liter of culture h⁻¹ were produced by means of direct biophotolysis. The maximum apparent light-to-hydrogen conversion efficiency expressed on PAR (photosynthetically active radiation) reached 3.22%, while PSII efficiency to perform direct biophotolysis was calculated to be 2.03%. These values are significantly higher than what has been reported in the literature.