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Corals have evolved as optimized photon augmentation systems, leading to space-efficient microalgal growth and outstanding photosynthetic quantum efficiencies. Light attenuation due to algal self-shading is a key limiting factor for the upscaling of microalgal cultivation. Coral-inspired light management systems could overcome this limitation and facilitate scalable bioenergy and bioproduct generation. Here, we develop 3D printed bionic corals capable of growing microalgae with high spatial cell densities of up to 10 9  cells mL −1 . The hybrid photosynthetic biomaterials are produced with a 3D bioprinting platform which mimics morphological features of living coral tissue and the underlying skeleton with micron resolution, including their optical and mechanical properties. The programmable synthetic microenvironment thus allows for replicating both structural and functional traits of the coral-algal symbiosis. Our work defines a class of bionic materials that is capable of interacting with living organisms and can be exploited for applied coral reef research and photobioreactor design. Corals have evolved as finely tuned light collectors. Here, the authors report on the 3D printing of coral-inspired biomaterials, that mimic the coral-algal symbiosis; these bionic corals lead to dense microalgal growth and can find applications in algal biotechnology and applied coral science.

Eukaryotic phytoplankton have a small global biomass but play major roles in primary production and climate. Despite improved understanding of phytoplankton diversity and evolution, we largely ignore the cellular bases of their environmental plasticity. By comparative 3D morphometric analysis across seven distant phytoplankton taxa, we observe constant volume occupancy by the main organelles and preserved volumetric ratios between plastids and mitochondria. We hypothesise that phytoplankton subcellular topology is modulated by energy-management constraints. Consistent with this, shifting the diatom Phaeodactylum from low to high light enhances photosynthesis and respiration, increases cell-volume occupancy by mitochondria and the plastid CO2-fixing pyrenoid, and boosts plastid-mitochondria contacts. Changes in organelle architectures and interactions also accompany Nannochloropsis acclimation to different trophic lifestyles, along with respiratory and photosynthetic responses. By revealing evolutionarily-conserved topologies of energy-managing organelles, and their role in phytoplankton acclimation, this work deciphers phytoplankton responses at subcellular scales.

Many of the demands in the production of microalgae at a technical scale cannot presently be met by state-of-the-art cultivation technologies based on suspensions. Immobilized cultivation using porous substrate bioreactors (PSBRs) is characterized by a reduction of liquid reaction volumes by several orders of magnitude and has solved several volume-related problems. Recently, PSBRs demonstrated potential for both established and novel applications in microalgal biotechnology, and first insights into biophysical processes have provided an understanding of the benefits of PSBR biofilm cultivation. Further efforts should primarily focus on scale-up and engineering challenges in this emerging field and, additionally, provide experience in the long-term operation of bioreactors. The results may contribute to assessing the technical and economic potential of PSBR cultivation. Porous substrate bioreactors (PSBRs) grow microalgae immobilized in dense biofilm cultures. They solve some substantial problems related to the high liquid volume and low culture densities attributed to state-of-the-art cultivation methods in microalgal biotechnology. Recently, proof of principle for several established and innovative products and applications in algal biotechnology and environmental biotechnology has been demonstrated. Scalability was demonstrated at a small pilot scale. The first insights into the biophysical processes occurring within PSBR biofilms have provided a basic understanding of some advantages of PSBR cultivation. Areal productivities compare favorably with highly productive closed suspension photobioreactors. The simple construction and low energy demands of PSBRs may indicate the significant economic potential of this novel microalgal cultivation system.

We examined responses of batch cultures of the marine microalga Nannochloropsis sp. to combined alterations in salinity (13, 27, and 40 g/l NaCl) and light intensity (170 and 700 μmol photons/m^sup 2^·s). Major growth parameters and lipid productivity (based on total fatty acid determination) were determined in nitrogen-replete and nitrogen-depleted cultures of an initial biomass of 0.8 and 1.4 g/l, respectively. On the nitrogen-replete medium, increases in light intensity and salinity increased the cellular content of dry weight and lipids due to enhanced formation of triacylglycerols (TAG). Maximum average productivity of ca. 410 mg TFA/l/d were obtained at 700 μmol photons/m^sup 2^·s and 40 g/l NaCl within 7 days. Under stressful conditions, content of the major LC-PUFA, eicosapentaenoic acid (EPA), was significantly reduced while TAG reached 25% of biomass. In contrast, lower salinity tended to improve major growth parameters, consistent with less variation in EPA contents. Combined higher salinity and light intensity was detrimental to lipid productivity under nitrogen starvation; biomass TFA content, and lipid productivity amounted for only 33% of DW and ca. 200 mg TFA/l/day, respectively. The highest biomass TFA content (ca. 47% DW) and average lipid productivity of ca. 360 mg TFA/l/day were achieved at 13 g/l NaCl and 700 μmol photons/m^sup 2^·s. Our data further support selecting Nannochloropsis as promising microalgae for biodiesel production. Moreover, appropriate cultivation regimes may render Nannochloropsis microalgae to produce simultaneously major valuable components, EPA, and TAG, while sustaining relatively high biomass growth rates. [PUBLICATION ABSTRACT]

In the current literature, the life cycle, technoeconomic, and resource assessments of microalgae-based biofuel production systems have relied on growth models extrapolated from laboratory-scale data, leading to a large uncertainty in results. This type of simplistic growth modeling overestimates productivity potential and fails to incorporate biological effects, geographical location, or cultivation architecture. This study uses a large-scale, validated, outdoor photobioreactor microalgae growth model based on 21 reactor- and species-specific inputs to model the growth of Nannochloropsis . This model accurately accounts for biological effects such as nutrient uptake, respiration, and temperature and uses hourly historical meteorological data to determine the current global productivity potential. Global maps of the current near-term microalgae lipid and biomass productivity were generated based on the results of annual simulations at 4,388 global locations. Maximum annual average lipid yields between 24 and 27 m ³·ha ⁻¹·y ⁻¹, corresponding to biomass yields of 13 to 15 g·m ⁻²·d ⁻¹, are possible in Australia, Brazil, Colombia, Egypt, Ethiopia, India, Kenya, and Saudi Arabia. The microalgae lipid productivity results of this study were integrated with geography-specific fuel consumption and land availability data to perform a scalability assessment. Results highlight the promising potential of microalgae-based biofuels compared with traditional terrestrial feedstocks. When water, nutrients, and CO ₂ are not limiting, many regions can potentially meet significant fractions of their transportation fuel requirements through microalgae production, without land resource restriction. Discussion focuses on sensitivity of monthly variability in lipid production compared with annual average yields, effects of temperature on productivity, and a comparison of results with previous published modeling assumptions.

Microalgae play a crucial role in ecosystems, from oxygen production to sustaining food webs and offering valuable applications in industry and environmental management. Increasing their productivity in terms of biomass yield, cultivation time, and nutritional or metabolite quality remains a major challenge. This study assessed the effects of 10 bioactive substances (including lactones, phytohormones, and natural extracts), four light wavelengths, and four CO₂ injection regimes on Arthrospira platensis, Chlorella vulgaris, Ankistrodesmus falcatus, and Tetradesmus dimorphus, using linear modeling and LSD (Least Significant Difference) post hoc tests. N-butyryl-DL-homoserine lactone significantly enhanced A. platensis growth (94.4%), while naphthaleneacetic acid and indole-3-butyric acid promoted T. dimorphus growth (138.1% and 115.5%, respectively). More accessible alternatives, such as Aloe vera and coconut water, also stimulated growth: A. platensis, C. vulgaris, and A. falcatus increased by 85.3%, 69.2%, and 87.7% with Aloe vera, while T. dimorphus increased 80.5% with coconut water. Regarding light quality, red light (600-700 nm) benefited A. platensis and A. falcatus (49.2% and 20.8%, respectively), whereas blue light (400-490 nm) favored C. vulgaris and T. dimorphus (57.7% and 31.5%, respectively). CO₂ injection further enhanced biomass production and carbon fixation, particularly in C. vulgaris and A. falcatus (73.5% and 53.5%, respectively). However, combined treatments did not produce additive effects, suggesting complex interactions. Overall, these findings demonstrate the potential of bioactive substances and environmental conditions to improve microalgal performance and highlight the importance of investigating synergistic effects and scalability for large-scale production.

Photosynthetic eukaryotic microalgae are key primary producers in the Antarctic sea ice environment. Anticipated changes in sea ice thickness and snow load due to climate change may cause substantial shifts in available light to these ice-associated organisms. This study used a laboratory-based experiment to investigate how light levels, simulating different sea ice and snow thicknesses, affect fatty acid (FA) composition in two ice associated microalgae species, the pennate diatom Nitzschia cf. biundulata and the dinoflagellate Polarella glacialis . FA profiling and transcriptomic analyses were used to compare the impact of three light levels: High (baseline culturing conditions 90 ± 1 μmol photons m −2 s −1 ), mid (10 ± 1 μmol photons m −2 s −1 ); and low (1.5 ± 1 μmol photons m −2 s −1 ) on each isolate. Both microalgal isolates had altered growth rates and shifts in FA composition under different light conditions. Nitzschia cf. biundulata exhibited significant changes in specific saturated and monounsaturated FAs, with a notable increase in energy storage-related FAs under conditions emulating thinner ice or reduced snow cover. Polarella glacialis significantly increased production of polyunsaturated FAs (PUFAs) in mid light conditions, particularly octadecapentaenoic acid (C18:5N-3), indicating enhanced membrane fluidity and synthesis of longer-chain PUFAs. Notably, C18:5N-3 has been identified as an ichthyotoxic molecule, with fish mortalities associated with other high producing marine taxa. High light levels caused down regulation of photosynthetic genes in N . cf. biundulata isolates and up-regulation in P . glacialis isolates. This and the FA composition changes show the variability of acclimation strategies for different taxonomic groups, providing insights into the responses of microalgae to light stress. This variability could impact polar food webs under climate change, particularly through changes in macronutrient availability to higher trophic levels due to species specific acclimation responses. Further research on the broader microalgal community is needed to clarify the extent of these effects.

The truncated light-harvesting antenna size3 (tla3) DNA insertional transformant of Chlamydomonas reinhardtii is a chlorophyll-deficient mutant with a lighter green phenotype, a lower chlorophyll (Chl) per cell content, and higher Chl a/b ratio than corresponding wild-type strains. Functional analyses revealed a higher intensity for the saturation of photosynthesis and greater light-saturated photosynthetic activity in the tla3 mutant than in the wild type and a Chl antenna size of the photosystems that was only about 40% of that in the wild type. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western-blot analyses showed that the tla3 strain was deficient in the Chl a/b light-harvesting complex. Molecular and genetic analyses revealed a single plasmid insertion in chromosome 4 of the tla3 nuclear genome, causing deletion of predicted gene g5047 and plasmid insertion within the fourth intron of downstream-predicted gene g5046. Complementation studies defined that gene g5047 alone was necessary and sufficient to rescue the tla3 mutation. Gene g5047 encodes a C. reinhardtii homolog of the chloroplast-localized SRP43 signal recognition particle, whose occurrence and function in green microalgae has not hitherto been investigated. Biochemical analysis showed that the nucleus-encoded and chloroplast-localized CrCpSRP43 protein specifically operates in the assembly of the peripheral components of the Chl a/b light-harvesting antenna. This work demonstrates that cpsrp43 deletion in green microalgae can be employed to generate tla mutants with a substantially diminished Chl antenna size. The latter exhibit improved solar energy conversion efficiency and photosynthetic productivity under mass culture and bright sunlight conditions.

Biofuels from algae are highly interesting as renewable energy sources to replace, at least partially, fossil fuels, but great research efforts are still needed to optimize growth parameters to develop competitive large-scale cultivation systems. One factor with a seminal influence on productivity is light availability. Light energy fully supports algal growth, but it leads to oxidative stress if illumination is in excess. In this work, the influence of light intensity on the growth and lipid productivity of Nannochloropsis salina was investigated in a flat-bed photobioreactor designed to minimize cells self-shading. The influence of various light intensities was studied with both continuous illumination and alternation of light and dark cycles at various frequencies, which mimic illumination variations in a photobioreactor due to mixing. Results show that Nannochloropsis can efficiently exploit even very intense light, provided that dark cycles occur to allow for re-oxidation of the electron transporters of the photosynthetic apparatus. If alternation of light and dark is not optimal, algae undergo radiation damage and photosynthetic productivity is greatly reduced. Our results demonstrate that, in a photobioreactor for the cultivation of algae, optimizing mixing is essential in order to ensure that the algae exploit light energy efficiently.