1,721,064 research outputs found
A new cryptic species of the unicellular red algal genus Dixoniella (Rhodellophyceae, Proteorhodophytina): Dixoniella giordanoi.
No full textDuring samplings aimed at isolating microalgal strains, a coccoid greyish-green alga was collected along the North Adriatic coasts (Mediterranean Sea, Italy) and grown in culture. The microalgal strain (named strain B1A) was then subjected to an integrative taxonomy approach in order to correctly identify it. Morphological and ultrastructural observations and phycobiliprotein content analysis were carried out, as well as molecular analyses based on the 18S rRNA, rbcL, psbA and plastid-encoded 23S rRNA genes. Phylogenetic placement and ultrastructural observations clearly indicated that strain B1A is a member of the red microalgal genus Dixoniella (Rhodellophyceae, Proteorhodophytina) and is distinct from the only species so far described for this taxon. Therefore, a new species was described to encompass the isolate from the North Adriatic Sea and another isolate from Japan (MF-G2), which was phylogenetically related to strain B1A: Dixoniella giordanoi sp. nov
Model-based optimization of microalgae growth in a batch plant
No full textThe economic sustainability of microalgaebased processes is still a major issue hindering the industrial application of such technologies. In this work, a mathematical model describing microalgae in varying light and temperature conditions is used to propose an optimized operation policy to increase productivity. The model is calibrated experimentally to describe the growth of Scenedesmus sp. cultivated in two outdoor pilot photobioreactors with different volumes and then used to maximize algal biomass productivity by proposing a
new harvesting policy of the culture. Experimental tests showed that a significant productivity increase is achievable using the optimized procedure. Simulated tests also highlighted that the additional implementation of an optimal temperature control strategy may lead to double biomass production
Role and regulation of class-C flavodiiron proteins in photosynthetic organisms
No full textThe regulation of photosynthesis is crucial to efficiently support the assimilation of carbon dioxide and to prevent photodamage. One key regulatory mechanism is the pseudo-cyclic electron flow (PCEF) mediated by class-C flavodiiron proteins (FLVs). These enzymes use electrons coming from Photosystem I (PSI) to reduce oxygen to water, preventing over-reduction in the acceptor side of PSI. FLVs are widely distributed among organisms performing oxygenic photosynthesis and they have been shown to be fundamental in many different conditions such as fluctuating light, sulfur deprivation and plant submersion. Moreover, since FLVs reduce oxygen they can help controlling the redox status of the cell and maintaining the microoxic environment essential for processes such as nitrogen fixation in cyanobacteria. Despite these important roles identified in various species, the genes encoding for FLV proteins have been lost in angiosperms where their activity could have been at least partially compensated by a more efficient cyclic electron flow (CEF). The present work reviews the information emerged on FLV function, analyzing recent structural data that suggest FLV could be regulated through a conformational change
Flavodiiron proteins in Physcomitrium patens: navigating the edge between photoprotection and efficiency
Full text linkSunlight is the primary energy source for photosynthetic organisms, driving electron transport that supports the synthesis of ATP and NADPH. In dynamic environmental conditions, photosynthetic electron transport requires continuous modulation to prevent over-reduction and safeguard against potential damage. Flavodiiron proteins (FLV) contribute to photoprotection by accepting electrons downstream of Photosystem I, reducing oxygen to water. FLV were shown to have a seminal role in response to abrupt changes in illumination intensity in various photosynthetic organisms, such as cyanobacteria, green algae, mosses, and gymnosperms but were lost during evolution of angiosperms. In this work, Physcomitrium patens plants with strong FLV accumulation, up to 20 times higher than WT, were isolated. Overexpressor plants exhibited faster activation of electron transport but did not gain additional tolerance to light fluctuations, suggesting that the contribution to photoprotection from the FLV was already saturated in WT plants. On the contrary, strong protein overexpression caused a growth penalty under steady low or high light intensity suggesting that FLV overaccumulation can be detrimental, at least in some conditions, opening hypotheses to explain why these proteins were lost during the evolution of angiosperms
Light intensity activation of alternative electron transport mechanisms in the moss Physcomitrium patens
Full text linkPhotosynthetic organisms exploit sunlight to drive an electron transport chain and obtain the chemical energy supporting their metabolism. In highly dynamic environmental conditions, excitation energy and electron transport need to be continuously modulated to prevent over-reduction and the consequent damage. An essential role in the regulation of electron transport is played by alternative electron transport mechanisms such as cyclic electron transport (CET) facilitated by PGRL1/PGR5 and NDH complex and pseudo-cyclic electron transport (PCET) mediated by the flavodiiron proteins (FLV) and the Mehler reaction. In this work mutant lines of the moss Physcomitrium patens depleted in PCET (flva KO) or CET (pgrl1/ndhm KO) were compared to wild-type plants for their ability to regulate photosynthetic electron transport in response to light fluctuations of different intensities. FLV activity enables a very fast increase in electron transport capacity but its impact is transient and becomes undetectable after 3 min from a light change. The FLV electron transport capacity is saturated at 100 μmol photons m−2 s−1 and does not increase even if exposed to stronger illumination. On the other hand, CET activation after an increase in illumination has a smaller contribution on electron transport capacity, but it provides a steady contribution for several minutes after a change in illumination intensity. Overall, these results demonstrate that light adapted plants CO2 fixation capacity needs approx. 3 min to adjust to different illumination intensities. In this interval CET and PCET enable adjusting temporary unbalances in electron transport, fully responding to 2–4 time increases in illumination. In case of larger increases, these mechanisms still contribute to protection from light damage by reducing the accumulation of electrons at PSI acceptor side. While the two mechanisms play an overlapping function, their activity shows distinctive kinetics and electron transport capacity thus they are complementary in ensuring optimal photoprotection
The xanthophyll cycle balances photoprotection and photosynthetic efficiency in the seawater alga Nannochloropsis oceanica
No full textPhotosynthetic reactions are continuously modulated to respond to highly dynamic environmental conditions. Balancing photosynthesis and photoprotection involves various mechanisms, which differ across phylogenetic groups. One such mechanism that is widespread in photosynthetic eukaryotes is the xanthophyll cycle, which involves the reversible light-dependent conversion between the carotenoids violaxanthin, antheraxanthin, and zeaxanthin. In this study, we investigated the role of the xanthophyll cycle in Nannochloropsis oceanica, a seawater microalga that possesses peculiarly high xanthophyll levels. To this end, we generated and characterized lines with increased levels of the enzymes involved in the xanthophyll cycle, i.e. violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). We demonstrated that the level of VDE and ZEP is the main factor controlling the overall reaction rates and dynamics of the xanthophyll cycle. Subsequent differences in the xanthophyll profile affect the activation of photoprotection mechanisms such as nonphotochemical quenching and tolerance to reactive oxygen species. Interestingly, VDE overexpression enhances high light tolerance, whereas increased ZEP levels facilitate faster recovery after light exposure but also heighten photosensitivity under certain conditions. In addition, light exposure strongly downregulates ZEP activity in Nannochloropsis. Taken together, these findings underscore the critical role of the xanthophyll cycle in regulating photosynthesis in Nannochloropsis. This cycle is not simply a mechanism that responds to excess illumination, but one that balances photoprotection and light-use efficiency under different environmental conditions
Role of heat dissipation mechanisms in Physcomitrella patens acclimation to different light conditions
No full textIn silico and biochemical analysis of Physcomitrella patens photosynthetic antenna: identification of subunits which evolved upon land adaptation.
No full textAcclimation of photosynthesis and lipids biosynthesis to prolonged nitrogen and phosphorus limitation in Nannochloropsis gaditana
No full textMicroalgae represent a potential sustainable source of molecules and materials and the improvement of the knowledge of their metabolic regulation is essential to maximize their potential. Nutrients deprivation stimulates the accumulation of reserve lipids, triacylglycerols but also inhibits photosynthesis with a negative impact on biomass production and therefore overall productivity. In this work, the seawater microalga Nannochloropsis gaditana was cultivated long term in a semi-continuous system where the concentrations of nitrogen or phosphorus were limiting but still sufficient to sustain growth indefinitely, to highlight the response to a long-term nutrient limitation and distinguishing it from the one to acute short-term stress. N. gaditana cells can acclimate to chronic nutrients limitation maintaining photosynthetic activity while also accumulating lipids. Both nitrogen and phosphorus limitation induced an increase of triacylglycerols content, although not by the induction of the synthesis of fatty acids but rather by modulating the fluxes of reduced carbon molecules toward lipid biosynthesis. Photosynthetic activity was maintained under P limitation while this was strongly affected by nitrogen depletion, where proteins of photosynthetic apparatus were largely reduced in content but still maintained their functionality and were able to achieve half of the biomass productivity with 30% of the nitrogen supply
Evolution of photoprotection mechanisms upon land colonization: evidence of PSBS-dependent NPQ in late Streptophyte algae.
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