Poster: Photosynthesis

Abs # 327: Photosynthetic Hydrogen Production

Presenter:	Melis, Tasios , melis@nature.berkeley.edu
Authors	Melis, Tasios  (A)   Chen, Hsu-Ching  (A)
Affiliations:	(A): University of California, Berkeley

The biochemistry of photosynthetic hydrogen production in green algae entails regulation of cellular metabolism and alterations in the photosynthesis/respiration ratio. Sulfate-deprivation of green algae is a useful tool to induce such changes. S-deprivation causes a re-direction of photosynthetic electron transport toward H2-production. Interplay between oxygenic photosynthesis, mitochondrial respiration, catabolism of endogenous substrate, and electron transport via the [Fe]-hydrogenase pathway is essential for this light-mediated H2-production. The process of photosynthetic H2-production could be sustained continuously for up to 4-days under S-deprivation, at the end of which cells need to go back to normal photosynthesis, via S-resupply, in order to recover lost metabolites. Cycling of H2-production upon S-deprivation and normal photosynthesis upon S-resupply could be repeated ad infinitum. Efforts to improve the continuity and yield of this H2-production process are focused on the use of a newly cloned Chlamydomonas reinhardtii sulfate permease gene (Sulp1, GenBank Accession No. AF467891 and AF481828). This gene is encoded by the nuclear genome, whereas the mature protein is targeted toward the chloroplast. By using antisense technology, evidence is provided for the function of the Sulp1 protein in the uptake of sulfate by the chloroplast, directly affecting de novo protein biosynthesis, protein turnover, and the repair of the photosynthetic apparatus from a frequently occurring photo-oxidative damage. Antisense transformants of the Sulp1 gene exhibited phenotypes of sulfate-starved cells, enhanced arylsulfatase (ARS) activity, altered photosynthesis/respiration ratio, and continuous H2-production in the presence of sulfate nutrients in the medium.