Temperature-sensitive PSII: a novel approach for sustained photosynthetic hydrogen production

Abstract

The need for energy and the associated burden are ever growing. It is crucial to develop new technologies for generating clean and efficient energy for society to avoid upcoming energetic and environmental crises. Sunlight is the most abundant source of energy on the planet. Consequently, it has captured our interest. Certain microalgae possess the ability to capture solar energy and transfer it to the energy carrier, H2. H2 is a valuable fuel, because its combustion produces only one by-product: water. However, the establishment of an efficient biophotolytic H2 production system is hindered by three main obstacles: (1) the hydrogen-evolving enzyme, [FeFe]-hydrogenase, is highly sensitive to oxygen; (2) energy conversion efficiencies are not economically viable; and (3) hydrogen-producing organisms are sensitive to stressful conditions in large-scale production systems. This study aimed to circumvent the oxygen sensitivity of this process with a cyclic hydrogen production system. This approach required a mutant that responded to high temperatures by reducing oxygen evolution. To that end, we randomly mutagenized the green microalgae, Chlamydomonas reinhardtii, to generate mutants that exhibited temperature-sensitive photoautotrophic growth. The selected mutants were further characterized by their ability to evolve oxygen and hydrogen at 25 and 37 °C. We identified four candidate mutants for this project. We characterized these mutants with PSII fluorescence, P700 absorbance, and immunoblotting analyses. Finally, we demonstrated that these mutants could function in a prototype hydrogen-producing bioreactor. These mutant microalgae represent a novel approach for sustained hydrogen production.

Temperature Sensitive Photosynthesis: Point Mutated CEF-G, PRK, or PsbO Act as Temperature-Controlled Switches for Essential Photosynthetic Processes

“…The mutants TSP1, TSP2, and TSP4 were produced on the background strain of C. reinhardtii 1A+ and were previously described ( Bayro-Kaiser and Nelson, 2016 ). The mutants were deposited in the public mutant bank “ ” with the respective numbers CC-5656, CC-5657 and CC-5669.…”

“…In an attempt to control photosynthetic activity to support continuous hydrogen production, we previously generated and isolated temperature-sensitive-photoautotrophic (TSP) mutants in C. reinhardtii (Bayro-Kaiser and Nelson, 2016). We randomly mutagenized cells by UV-exposure and identified relevant mutants that were NOT able to grow (photoautotrophically) at elevated temperature.…”

“…Thorough phenotyping of all TSP mutants enabled selecting the four most interesting mutants according to a variety of criteria (e.g., no abnormal phenotype at the permissive temperature, viability of partial photosynthetic reactions at restrictive temperature, capacity to recover from heat treatment). The selected mutants were called TSP1, TSP2, TSP3, and TSP4 and their relevance for hydrogen production was described in a previous report (Bayro-Kaiser and Nelson, 2016).…”

Biomass from microalgae: the potential of domestication towards sustainable biofactories

“…Finally, microalgae and cyanobacteria can produce bio-hydrogen through photo-fermentation, in an anaerobic process involving oxidation of ferredoxin by the hydrogenase enzyme [ 63 , 64 ]. Although biological H 2 shows great promise for generating future, large scale sustainable energy, a number of bottlenecks still limit its production [ 65 ]; however, recent result [ 66 ] identified in C. reinhardtii promising targets for genetic engineering of H 2 production capacity while the use of temperature-sensitive conditional PSII mutants has been proposed in order to separate the oxygenic biomass-accumulating phase from the oxygen sensitive hydrogenase activity [ 67 ].…”

Microalgal hydrogen production: prospects of an essential technology for a clean and sustainable energy economy

“…However, none of these systems have been tested yet at a large scale, and their feasibility needs to be validated. In a different approach, our lab proposed using temperature to control PSII activity (Mazor et al 2012 ; Bayro-Kaiser and Nelson 2016 ). For this purpose, randomly generated mutants were screened for PSII temperature sensitivity.…”