title: Biochemical and morphological characterization of sulfur-deprived and H2-producing Chlamydomonas reinhardtii (green alga).
abstract: Sulfur deprivation in green algae causes reversible inhibition of photosynthetic activity. In the absence of S, rates of photosynthetic O2 evolution drop below those of O2 consumption by respiration. As a consequence, sealed cultures of the green alga Chlamydomonas reinhardtii become anaerobic in the light, induce the "Fe-hydrogenase" pathway of electron transport and photosynthetically produce H2 gas. In the course of such H2-gas production cells consume substantial amounts of internal starch and protein. Such catabolic reactions may sustain, directly or in directly, the H2-production process. Profile analysis of selected photosynthetic proteins showed a precipitous decline in the amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) as a function of time in S deprivation, a more gradual decline in the level of photosystem (PS) II and PSI proteins, and a change in the composition of the PSII light-harvesting complex (LHC-II). An increase in the level of the enzyme Fe-hydrogenase was noted during the initial stages of S deprivation (0-72 h) followed by a decline in the level of this enzyme during longer (t >72 h) S-deprivation times. Microscopic observations showed distinct morphological changes in C. reinhardtii during S deprivation and H2 production. Ellipsoid-shaped cells (normal photosynthesis) gave way to larger and spherical cell shapes in the initial stages of S deprivation and H2 production, followed by cell mass reductions after longer S-deprivation and H2-production times. It is suggested that, under S-deprivation conditions, electrons derived from a residual PSII H2O-oxidation activity feed into the hydrogenase pathway, thereby contributing to the H2-production process in Chlamydomonas reinhardtii. Interplay between oxygenic photosynthesis, mitochondrial respiration, catabolism of endogenous substrate, and electron transport via the hydrogenase pathway is essential for this light-mediated H2-production process.
authors.affiliation: Department of Plant and Microbial Biology, University of California, Berkeley 94720-3102, USA.
authors.forename: Liping
authors.initials: L
authors.lastname: Zhang
authors.forename: Thomas
authors.initials: T
authors.lastname: Happe
authors.forename: Anastasios
authors.initials: A
authors.lastname: Melis
mesh_terms: D000693:Anaerobiosis; D000818:Animals; D019069:Cell Respiration / Q000187:drug effects; D016825:Chlamydomonas reinhardtii / Q000737:chemistry / Q000254:growth & development / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004579:Electron Transport / Q000187:drug effects; D006859:Hydrogen / Q000378:metabolism*; D006864:Hydrogenase / Q000187:drug effects / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D008027:Light; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects*; D010940:Plant Proteins / Q000378:metabolism; D012273:Ribulose-Bisphosphate Carboxylase / Q000187:drug effects / Q000378:metabolism; D013213:Starch / Q000378:metabolism; D013455:Sulfur / Q000172:deficiency / Q000494:pharmacology*
chemical_list: D007506:Iron-Sulfur Proteins; D010940:Plant Proteins; D002734:Chlorophyll; D013455:Sulfur; D006859:Hydrogen; D013213:Starch; C118830:iron hydrogenase; D006864:Hydrogenase; D012273:Ribulose-Bisphosphate Carboxylase; D010100:Oxygen