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1.
Proc Natl Acad Sci U S A ; 120(25): e2214119120, 2023 06 20.
Article in English | MEDLINE | ID: mdl-37307488

ABSTRACT

Life on earth depends on photosynthetic primary producers that exploit sunlight to fix CO2 into biomass. Approximately half of global primary production is associated with microalgae living in aquatic environments. Microalgae also represent a promising source of biomass to complement crop cultivation, and they could contribute to the development of a more sustainable bioeconomy. Photosynthetic organisms evolved multiple mechanisms involved in the regulation of photosynthesis to respond to highly variable environmental conditions. While essential to avoid photodamage, regulation of photosynthesis results in dissipation of absorbed light energy, generating a complex trade-off between protection from stress and light-use efficiency. This work investigates the impact of the xanthophyll cycle, the light-induced reversible conversion of violaxanthin into zeaxanthin, on the protection from excess light and on biomass productivity in the marine microalgae of the genus Nannochloropsis. Zeaxanthin is shown to have an essential role in protection from excess light, contributing to the induction of nonphotochemical quenching and scavenging of reactive oxygen species. On the contrary, the overexpression of zeaxanthin epoxidase enables a faster reconversion of zeaxanthin to violaxanthin that is shown to be advantageous for biomass productivity in dense cultures in photobioreactors. These results demonstrate that zeaxanthin accumulation is critical to respond to strong illumination, but it may lead to unnecessary energy losses in light-limiting conditions and accelerating its reconversion to violaxanthin provides an advantage for biomass productivity in microalgae.


Subject(s)
Microalgae , Biomass , Zeaxanthins , Xanthophylls
2.
J Biotechnol ; 357: 28-37, 2022 Sep 20.
Article in English | MEDLINE | ID: mdl-35931238

ABSTRACT

Oleaginous microalgae represent potential feedstocks for the sustainable production of lipids thanks to their ability to accumulate triacylglycerols (TAGs). TAG accumulation in several algal species is strongly induced under specific conditions such as nutrient deprivation and high light which, however, also negatively impact growth. Genetic modification of lipogenic pathways can potentially enhance TAG accumulation without negatively affecting growth, avoiding the trade-off between biomass and lipid productivity. In this study, the phospholipid: diacylglycerol acyltransferase (PDAT), an enzyme involved in membrane lipid recycling, was overexpressed in the seawater alga Nannochloropsis gaditana. PDAT overexpression induced increased TAG content in actively growing algae cultures while no effects were observed in conditions naturally stimulating strong lipid accumulation such as high light and nitrogen starvation. The increase of TAG content was confirmed also in a strain cultivated in industrially relevant conditions even though PDAT overexpression, if too strong, the gene overexpression becomes detrimental for growth in the longer term. Results overall suggest that genetic modulation of the PDAT gene represents a promising strategy to increase microalgae lipid content by minimizing negative effects on biomass productivity.


Subject(s)
Microalgae , Stramenopiles , Membrane Lipids/metabolism , Microalgae/genetics , Microalgae/metabolism , Nitrogen/metabolism , Plants/metabolism , Stramenopiles/genetics , Stramenopiles/metabolism , Triglycerides/metabolism
3.
Bioresour Technol ; 320(Pt B): 124379, 2021 Jan.
Article in English | MEDLINE | ID: mdl-33189041

ABSTRACT

Poly-ß-hydroxybutyrate (PHB) is a biodegradable biopolymer that may replace fossil-based plastics reducing its negative environmental impact. One highly sustainable strategy to produce these biopolymers is the exploitation of photosynthetic microorganisms that use sunlight and CO2 to produce biomass and subsequently, PHB. Exploring environmental biological diversity is a powerful tool to find resilient microorganisms potentially exploitable to produce bioproducts. In this work, a cyanobacterium (Synechocystis sp.) isolated from a contaminated area close to an important industrial complex was shown to produce PHB under different culture conditions. Carbon, nutrients supply and light intensity impact on biomass and PHB productivity were assessed, showing that the highest yield of PHB achieved was 241 mg L-1 (31%dcw) under high light intensity. Remarkably this condition not only stimulated PHB accumulation by 70% compared to other conditions tested but also high cellular duplication rate, maximizing the potential of this strain for PHB production.


Subject(s)
Synechocystis , Carbon , Hydroxybutyrates , Polyesters
4.
Plant Cell Physiol ; 61(1): 41-52, 2020 Jan 01.
Article in English | MEDLINE | ID: mdl-31511895

ABSTRACT

In nature, photosynthetic organisms are exposed to highly dynamic environmental conditions where the excitation energy and electron flow in the photosynthetic apparatus need to be continuously modulated. Fluctuations in incident light are particularly challenging because they drive oversaturation of photosynthesis with consequent oxidative stress and photoinhibition. Plants and algae have evolved several mechanisms to modulate their photosynthetic machinery to cope with light dynamics, such as thermal dissipation of excited chlorophyll states (non-photochemical quenching, NPQ) and regulation of electron transport. The regulatory mechanisms involved in the response to light dynamics have adapted during evolution, and exploring biodiversity is a valuable strategy for expanding our understanding of their biological roles. In this work, we investigated the response to fluctuating light in Nannochloropsis gaditana, a eukaryotic microalga of the phylum Heterokonta originating from a secondary endosymbiotic event. Nannochloropsis gaditana is negatively affected by light fluctuations, leading to large reductions in growth and photosynthetic electron transport. Exposure to light fluctuations specifically damages photosystem I, likely because of the ineffective regulation of electron transport in this species. The role of NPQ, also assessed using a mutant strain specifically depleted of this response, was instead found to be minor, especially in responding to the fastest light fluctuations.


Subject(s)
Light , Photosynthesis/physiology , Stramenopiles/metabolism , Symbiosis/physiology , Biodiversity , Electron Transport/physiology , Oxidative Stress , Photosystem I Protein Complex/metabolism , Photosystem I Protein Complex/radiation effects , Plants/metabolism , Stramenopiles/growth & development , Stramenopiles/radiation effects
5.
Physiol Plant ; 166(1): 380-391, 2019 May.
Article in English | MEDLINE | ID: mdl-30578540

ABSTRACT

The massive increase in carbon dioxide concentration in the atmosphere driven by human activities is causing huge negative consequences and new sustainable sources of energy, food and materials are highly needed. Algae are unicellular photosynthetic microorganisms that can provide a highly strategic contribution to this challenge as alternative source of biomass to complement crops cultivation. Algae industrial cultures are commonly limited by light availability, and biomass accumulation is strongly dependent on their photon-to-biomass conversion efficiency. Investigation of algae photosynthetic metabolism is thus strategic for the generation of more efficient strains with higher productivity. Algae are cultivated at industrial scale in conditions highly different from the natural niches they adapted to and strains development efforts must fully consider the seminal influence on productivity of regulatory mechanism of photosynthesis as well as of cultivation parameters like cells concentration, light distribution in the culture, mixing, nutrients and carbon dioxide availability. In this review we will focus in particular on how mathematical models can account for the complex influence of all environmental parameters and can be exploited for development of improved algae strains.


Subject(s)
Microalgae/metabolism , Photosynthesis/physiology , Biomass , Biotechnology , Carbon Dioxide/metabolism
6.
Metab Eng ; 44: 337-347, 2017 11.
Article in English | MEDLINE | ID: mdl-29128647

ABSTRACT

The optimization of algae biomass productivity in industrial cultivation systems requires genetic improvement of wild type strains isolated from nature. One of the main factors affecting algae productivity is their efficiency in converting light into chemical energy and this has been a major target of recent genetic efforts. However, photosynthetic productivity in algae cultures depends on many environmental parameters, making the identification of advantageous genotypes complex and the achievement of concrete improvements slow. In this work, we developed a mathematical model to describe the key factors influencing algae photosynthetic productivity in a photobioreactor, using experimental measurements for the WT strain of Nannochloropsis gaditana. The model was then exploited to predict the effect of potential genetic modifications on algae performances in an industrial context, showing the ability to predict the productivity of mutants with specific photosynthetic phenotypes. These results show that a quantitative model can be exploited to identify the genetic modifications with the highest impact on productivity taking into full account the complex influence of environmental conditions, efficiently guiding engineering efforts.


Subject(s)
Genetic Engineering , Models, Biological , Photosynthesis/physiology , Stramenopiles , Stramenopiles/genetics , Stramenopiles/metabolism
7.
Biotechnol Biofuels ; 8: 161, 2015.
Article in English | MEDLINE | ID: mdl-26413160

ABSTRACT

BACKGROUND: The productivity of an algal culture depends on how efficiently it converts sunlight into biomass and lipids. Wild-type algae in their natural environment evolved to compete for light energy and maximize individual cell growth; however, in a photobioreactor, global productivity should be maximized. Improving light use efficiency is one of the primary aims of algae biotechnological research, and genetic engineering can play a major role in attaining this goal. RESULTS: In this work, we generated a collection of Nannochloropsis gaditana mutant strains and screened them for alterations in the photosynthetic apparatus. The selected mutant strains exhibited diverse phenotypes, some of which are potentially beneficial under the specific artificial conditions of a photobioreactor. Particular attention was given to strains showing reduced cellular pigment contents, and further characterization revealed that some of the selected strains exhibited improved photosynthetic activity; in at least one case, this trait corresponded to improved biomass productivity in lab-scale cultures. CONCLUSIONS: This work demonstrates that genetic modification of N. gaditana has the potential to generate strains with improved biomass productivity when cultivated under the artificial conditions of a photobioreactor.

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