RECENT KEY PUBLICATIONS
Nagy et al., (2021)
Biores. Technol. 333: 125217
Earlier, we established a photoautotrophic H2 production system based on anaerobic induction, where the Calvin-Benson cycle is inactive and O2 scavenged by an absorbent. In this paper, we employed thin layer cultures, resulting in a three-fold increase in H2 production relative to bulk CC-124 cultures. Productivity was maintained when increasing the light intensity to 1000 µmol photons m-2s−1 and the cell density to 150 µg chlorophyll/ml. Remarkably, the L159I-N230Y photosystem II mutant and the pgrl1 photosystem I cyclic electron transport mutant produced 50% more H2 than CC-124, while the pgr5 mutant generated 250% more (1.2 ml H2/ml culture in six days). The photosynthetic apparatus of the pgr5 mutant and its in vitro HydA activity remained remarkably stable.
Podmaniczki et al., (2021)
Physiol. Plantarum 171: 232-245
In this study, we acquired knowledge on the role of ascorbate in dark‐induced leaf senescence using Arabidopsis thaliana as a model organism. One of the earliest effects of prolonged darkness is the inactivation of oxygen‐evolving complexes (OEC). We found that ascorbate inactivates the OEC in prolonged darkness by over‐reducing the Mn‐complex that is probably enabled by a dark‐induced dissociation of the extrinsic OEC subunits. Our study is an example that ascorbate may negatively affect certain cellular processes and thus its concentration and localization need to be highly controlled.
Ascorbate deficiency does not limit non-photochemical quenching in Chlamydomonas reinhardtii
Vidal-Meireles et al., (2020)
Plant Physiol. 182: 597–611
In this paper we demonstrated that Chlorophycean violaxanthin de-epoxidase found in C. reinhardtii does not require ascorbate as a reductant. The rapidly induced, energy-dependent non-photochemical quenching component was not limited by ascorbate deficiency either. On the other hand, a reactive oxygen species-induced photoinhibitory quenching component was greatly enhanced upon ascorbate deficiency. These results demonstrate that ascorbate has distinct roles in non-photochemical quenching in C. reinhardtii as compared to vascular plants.
Paradigm shift in algal H2 production: Bypassing competitive processes
Tóth SZ, Yacoby I (2019)
Trends Biotechnol 37: 1159-1163
Green algae can produce hydrogen photosynthetically using their efficient but oxygen-sensitive hydrogenases. In this paper we overview recently developed hydrogen production strategies that aim at bypassing the competing Calvin-Benson cycle to provide a promising route for scaling up algal hydrogen production.
The mechanism of photosystem II inactivation during sulphur deprivation-induced H2 production in Chlamydomonas reinhardtii
Nagy et al., (2018)
Plant J 94: 548-561
In the green alga Chlamydomonas reinhardtii, sulphur limitation causes a large number of physiological changes, including the inactivation of photosystem II (PSII), leading to the establishment of hypoxia, essential for the increase in hydrogenase expression and activity. In this paper we show that sulphur limitation imposes oxidative stress early on, which leads to strong ascorbate accumulation. In the mM range, ascorbate may inactivate the oxygen‐evolving complex and provide electrons to PSII, albeit at a low rate. In the absence of a functional donor side and sufficient electron transport, PSII reaction centers are inactivated and degraded.
Water-splitting-based, sustainable, and efficient H2 production in green algae as achieved by substrate limitation of the Calvin-Benson-Bassham cycle
Nagy et al., (2018)
Biotechnol Biofuels 11: 69
We reported on the establishment of a novel H2 production method by green algae that is based on a short anaerobic induction, keeping the Calvin–Benson cycle inactive by substrate limitation and preserving hydrogenase activity by applying a simple catalyst to remove the evolved O2. Cultures remained photosynthetically active for several days, with the electrons feeding the hydrogenases mostly derived from water. The amount of H2 produced is remarkable and the process is photoautotrophic.
Our protocol demonstrated that it is possible to sustainably use algal cells as whole-cell catalysts for H2 production, which enables industrial application of algal biohydrogen production.
See also: Nagy V and Tóth SZ (2017) European Patent pending (EPA 17155168.2).
Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress-induced response via the VTC2 gene encoding GDP-l-galactose phosphorylase
Vidal-Meireles et al. (2017)
New Phytol 214: 668-681
Ascorbate plays essential roles in plants; however, little was known about its biosynthesis in algae. In this study we demonstrated that in green algae ascorbate biosynthesis occurs via the Smirnoff-Wheeler pathway, just like in higher plants. In addition, we showed that: ascorbate biosynthesis is rapidly induced by reactive oxygen species; in contrast to plants, there is no circadian regulation of ascorbate biosynthesis; photosynthesis is not required per se for ascorbate biosynthesis; and Chlamydomonas VTC2 lacks negative feedback regulation by ascorbate in the physiological concentration range.