The Involvement of Hydrogen-producing and ATP-dependent NADPH-consuming Pathways in Setting the Redox Poise in the Chloroplast of Chlamydomonas reinhardtii in Anoxia

Abstract

Background: Shift to anoxia promotes the over-reduction of photosystem I electron acceptors. Results: This over-reduction can be relieved by the activation of several pathways. Conclusion: The two mains pathways are the ATP-dependent CO 2 fixation pathway and the ATP-independent hydrogenase. Significance: We disentangle the role of the various NADPH-consuming pathways in setting the redox poise in the chloroplast of unicellular photosynthetic algae.

Induction of Photosynthetic Carbon Fixation in Anoxia Relies on Hydrogenase Activity and Proton-Gradient Regulation-Like1-Mediated Cyclic Electron Flow in Chlamydomonas reinhardtii

“…In the two wild-type strains, in the pgrl1 mutant and in the pgrl1::PGRL1 complemented strain, R ph was about 20 e -s -1 PS -1 and J H2 was about 20 e -s -1 PSI -1 , which represents about 40% of the maximal capacity measured for hydrogenase . In the wild type, 20 e -s -1 PSI -1 corresponds to an H 2 production rate of 0.58 mmol H 2 mg chlorophyll -1 min -1 , which is compatible with recent published values of approximately 0.25 to 0.36 mmol H 2 mg chlorophyll -1 min -1 (Tolleter et al, 2011;Clowez et al, 2015). On the contrary, in the two mutants lacking hydrogenase activity (hydg-2 and pgrl1 hydg-2), neither hydrogen production, nor significant photosynthetic activity, was detected after 10 s of illumination (Table II).…”

“…The bidirectional Ni-Fe hydrogenase could also dispose of excess of reducing equivalents during fermentation in dark anaerobic conditions, helping to generate ATP and maintaining homeostasis (Barz et al, 2010). A similar role for hydrogenase in setting the redox poise in the chloroplast of C. reinhardtii in anoxia has been recently uncovered (Clowez et al, 2015).…”

Microoxic Niches within the Thylakoid Stroma of Air-Grown Chlamydomonas reinhardtii Protect [FeFe]-Hydrogenase and Support Hydrogen Production under Fully Aerobic Environment

“…The reasons for this absence are vague, but they could be related to differences in the growth environments. Microalgae naturally reside in ponds, wet soils, and lakes (Clowez et al, 2015), and have a tendency to swim into deeper water layers as a defense mechanism against intense light. Hence, they occasionally face fluctuating levels of oxygen in their proximate liquid or soil surroundings.…”

Microalgal Hydrogen Production

“…Hydrogenase activity can also be maintained by removing oxygen from the cells . Glucose oxidase is always used to consume the oxygen in the algae culture with glucose as substrate . Pyruvate oxidase ( PoX ) in E. coli reacts with oxygen to catalyze the oxidative decarboxylation of pyruvate to acetyl‐phosphate, hydrogen peroxide and carbon dioxide, leading to the consumption of oxygen .…”