Μmol Photons Research Articles

Photosynthetic Pigments Changes of Three Phenotypes of Picocyanobacteria Synechococcus sp. under Different Light and Temperature Conditions

It is estimated that the genus Synechococcus is responsible for about 17% of net primary production in the Global Ocean. Blooms of these organisms are observed in tropical, subtropical and even temperate zones, and they have been recorded recently even beyond the polar circle. The long-term scenarios forecast a growing expansion of Synechococcus sp. and its area of dominance. This is, among others, due to their high physiological plasticity in relation to changing environmental conditions. Three phenotypes of the genus Synechococcus sp. (Type 1, Type 2, and Type 3a) were tested in controlled laboratory conditions in order to identify their response to various irradiance (10, 55, 100 and 145 µmol photons m−2 s−1) and temperature (15, 22.5 and 30 °C) conditions. The highest total pigment content per cell was recorded at 10 μmol photons m−2 s−1 at all temperature variants with the clear dominance of phycobilins among all the pigments. In almost every variant the highest growth rate was recorded for the Type 1. The lowest growth rates were observed, in general, for the Type 3a. However, it was recognized to be less temperature sensitive in comparison to the other two types and rather light-driven with the highest plasticity and adaptation potential. The highest amounts of carotenoids were produced by Type 2 which also showed signs of the cell stress even around 55 μmol photons m−2 s−1 at 15 °C and 22.5 °C. This may imply that the Type 2 is the most susceptible to higher irradiances. Picocyanobacteria Synechococcus sp. require less light intensity to achieve the maximum rate of photosynthesis than larger algae. They also tolerate a wide range of temperatures which combined together make them gain a powerful competitive advantage. Our results will provide key information for the ecohydrodynamical model development. Thus, this work would be an important link in forecasting future changes in the occurrence of these organisms in the context of global warming.

Influence of variable salinity and low light on copper accumulation in the potential seagrass bioindicator, Zostera muelleri

Utilising a potential coastal trace element bioindicator requires understanding its accumulation patterns under varying environmental scenarios. The present study aimed to understand, from two experiments, the influence and effect of low light (15.3 μmol photons m−2 s−1) and variable salinity (normal 36 and reduced 29) on Zostera muelleri accumulating variable Cu concentrations (control, low 5 μg L−1 and high 50 μg L−1) in order to determine its capability as a potential trace element bioindicator. Initial (24 h) leaf Cu concentration was in proportion to exposure Cu concentrations, irrespective of manipulated environmental conditions, suggesting passive accumulation. Final below-ground Cu concentrations, during the low light experiment, significantly increased over time, suggesting active Cu accumulation. Zostera muelleri leaves could act as a Cu bioindicator at times of reduced light and salinity while further interpretation is required of below-ground Cu concentrations. It is recommended that Z. muelleri could be utilised as a Cu bioindicator.

Effects of gradual and sudden changes of salinity and light supply for astaxanthin production in Haematococcus pluvialis (Chlorophyceae)

Astaxanthin, a carotenoid naturally synthesized by Haematococcus pluvialis, is economically important for the nutraceutical, pharmaceutical and food industries due to its high antioxidant and anti-inflammatory properties. We investigated astaxanthin accumulation in H. pluvialis after stepwise versus suddenly increased light supply and salt (NaCl) concentrations. Light was increased from 75 to 150, and then to the final intensity of 350 μmol photons m –2 s–1 in three-day intervals. The effect of gradually increased salt concentration was examined with two steps from 0.2 to the final concentration of 0.8 % (w/v) in three-day intervals. The overall induction period for astaxanthin accumulation was 13 days. Out of all treatments, stepwise increased light supply resulted in highest cell viability and highest astaxanthin accumulation with 15.76 ± 0.88 mg g –1 dry mass. It is an energy-saving, appropriate strategy to achieve optimal astaxanthin accumulation. It moreover resulted in the least biomass loss, which is caused by the provided stress conditions.

The Influence of Light and Nutrient Starvation on Morphology, Biomass and Lipid Content in Seven Strains of Green Microalgae as a Source of Biodiesel

The development of clean and renewable energy sources is currently one of the most important challenges facing the world. Although research interests in algae-based energy have been increasing in the last decade, only a small percentage of the bewildering diversity exhibited by microalgae has been investigated for biodiesel production. In this work, seven strains of green microalgae belonging to the genera Scenedesmus, Tetradesmus and Desmodesmus were grown in liquid medium with or without a nitrogen (N) source—at two different irradiances (120 ± 20 and 200 ± 20 μmol photons m−2 s−1)—to evaluate biomass production and FAME (fatty acid methyl esters) content for biodiesel production. The strains of Tetradesmus obliquus and Desmodesmus abundans grown in N-deprived medium showed the highest FAME content (22.0% and 34.6%, respectively); lipid profile characterization highlighted the abundance of saturated FAME (as C16:0 and C18:0) that favors better viscosity (flow properties) and applicability of biodiesel at low temperatures. Light microscopy and confocal laser scanning microscopy observations were employed as a fast method to monitor the vital status of cells and lipid droplet accumulation after Nile red staining in different culture conditions.

Abstract 25: Skeletonema marinoi (diatom) extracts are endowed with promising cancer preventive properties in prostate cancer cells

Abstract The exploration of natural antioxidants for nutraceuticals and pharmaceuticals industries has recently increased. In this scenario, marine microorganisms, represent underestimated sources of bioactive products endowed with beneficial effects on health, that include anti-oxidant, anti-tumor and anti-angiogenic activities. Here, we tested the potential cancer preventive activities of extracts from the marine coastal diatom Skeletonema marinoi Sarno and Zingone (CCMP 2092) on prostate cancer cells, in vitro. Skeletonema marinoi was grown under a sinusoidal light distribution with a midday peak of 150 μmol photons m−2 s−1, and then, once cells reached the exponential phase, shifted to a sinusoidal light distribution with a higher midday peak light intensity of 600 μmol photons m−2 s−1. This high light condition induces in cells the synthesis of antioxidant and protective molecules. Total wet biomass was collected and chemically extracted by methanol solvent. The dried extract was tested as a food supplement on prostate (PC-3), as compared to normal prostate epithelium. Gene expression analysis was performed by qPCR, measuring the variation of 365 different genes involved in the apoptosis and immunogenic cell death pathways. Treatments with Skeletonema marinoi extracts (1-10-100 µg ml-1) resulted in a statistically significant, dose dependent, antiproliferative (inhibition at 70% of cell viability at 100 µg ml-1) and pro-apoptotic effects in PC-3 cells, while sparing normal epithelial prostatic cells. Among the gene panel analysed as key indicators of the PC3 cell fate in terms of signalling pathway prediction, we observed up/down regulation of APAF1, BAD, BAG1, BAG3, BAK1, BAX, BCL2, BCL2L1, BCL2L13, BCL2L2, BCL3, BDNF, BECN1, BFAR, BID, BIK, BIRC2, BIRC3, BIRC6, BNIP1, BOK, BRAF, BRCA1, BRE, CARD17, CARD9, CASP1-2-3-4-5-6-7-10-14, CBX4, CRADD, DEDD, DHCR24, FADD, FAS, FASLG, FASTK. The integrated gene expression analysis revealed necroptosis activation in cells with the up-regulation of the inflammatory mediators such as F2R, F2, IL18-19-A-31RA, SOCS2, SOCS3 genes and the downregulation of the angiogenic factors such as ALOX12, ALOX15B, PIK3CA, PIK3R2, and VEGF genes. One of the main candidates as compounds responsible for such cancer preventive activities is the diatom-xanthophyll photoprotective diatoxanthin, probably in synergy with other molecules. Further metabolomics analysis on the extracts will help in understanding and interpretation of the results. These results demonstrate promising cancer preventive activities of Skeletonema marinoi extracts in PC3 cell lines. This confirms microalgal-derived drugs as potential relevant source of nutraceutical novel food and candidate as potential dietary intervention in cancer prevention approaches. Citation Format: Clementina Sansone, Piscitelli Concetta, Galasso Christian, Smerilli Arianna, Bruno Antonino, Noonan Douglas, Albini Adriana, Brunet Christophe. Skeletonema marinoi (diatom) extracts are endowed with promising cancer preventive properties in prostate cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 25.

Inorganic carbon utilization of tropical calcifying macroalgae and the impacts of intensive mariculture-derived coastal acidification on the physiological performance of the rhodolith Sporolithon sp.

Fish farming in coastal areas has become an important source of food to support the world’s increasing population. However, intensive and unregulated mariculture activities have contributed to changing seawater carbonate chemistry through the production of high levels of respiratory CO2. This additional CO2, i.e. in addition to atmospheric inputs, intensifies the effects of global ocean acidification resulting in localized extreme low pH levels. Marine calcifying macroalgae are susceptible to such changes due to their CaCO3 skeleton. Their physiological response to CO2-driven acidification is dependent on their carbon physiology. In this study, we used the pH drift experiment to determine the capability of 9 calcifying macroalgae to use one or more inorganic carbon (Ci) species. From the 9 species, we selected the rhodolith Sporolithon sp. as a model organism to investigate the long-term effects of extreme low pH on the physiology and biochemistry of calcifying macroalgae. Samples were incubated under two pH treatments (pH 7.9 = ambient and pH 7.5 = extreme acidification) in a temperature-controlled (26 ± 0.02 °C) room provided with saturating light intensity (98.3 ± 2.50 μmol photons m−2 s−1). After the experimental treatment period (40 d), growth rate, calcification rate, nutrient uptake rate, organic content, skeletal CO3−2, pigments, and tissue C, N and P of Sporolithon samples were compared. The pH drift experiment revealed species-specific Ci use mechanisms, even between congenerics, among tropical calcifying macroalgae. Furthermore, long-term extreme low pH significantly reduced the growth rate, calcification rate and skeletal CO3−2 content by 79%, 66% and 18%, respectively. On the other hand, nutrient uptake rates, organic matter, pigments and tissue C, N and P were not affected by the low pH treatments. Our results suggest that the rhodolith Sporolithon sp. is susceptible to the negative effects of extreme low pH resulting from intensive mariculture-driven coastal acidification.

Optimization of the production of lipids and carotenoids in the microalga Golenkinia aff. brevispicula

Microalgae are a promising platform to produce natural pigments and lipids when compared to traditional sources, since they present faster growth and biomass productivity and there is a wide diversity that has not been studied yet. The green microalgae belonging to the genus Golenkinia presents few reports of its biomass production and applications. In this work, the productivity of lipids and carotenoids was studied in the strain Golenkinia aff. brevispicula FAUBA-3 using a two-stage cultivation system: a first step for biomass production under semicontinuous cultures, and a second step for the accumulation of lipids and carotenoids under batch salinity stress (35 g L−1). The highest biomass productivity (0.92 g L−1 day−1) was obtained under a dilution rate of 0.4 day−1. The growth rate (μ) was a hyperbolic function of average irradiance inside the culture (Eav). The optimum Eav was 88.4 μmol photons m−2 s−1 and the maximum specific growth rate (μmax) was 0.85 day−1. Photoinhibition was observed above 570 μmol photons m−2 s−1 of Eav. The best photosynthetic performance was obtained at 0.2 day−1 dilution rate but with lower biomass productivity due to nutrients and light limitation. High content of protein (30% DW) and polyunsaturated fatty acids (50% of total PUFAs) and low content of carbohydrates (19% DW) were observed at high dilution rate, and the opposite response at low dilution rate. In the second culture stage, an increase of salinity induced lipid and carotenoid accumulation which improved the productivity to 89 mg L−1 day−1 and 1.3 mg L−1 day−1 of total lipids and carotenoids respectively compared to one-stage culture. Lutein, β-carotene and astaxanthin were the main carotenoid identified in a decreasing order. Those results confirm that two-stage culture is an adequate strategy to optimize the carotenoid and lipid productivity in the promising strain Golenkinia FAUBA-3.

Nitrification of anaerobic digestate using a consortium of microalgae and nitrifiers in an open photobioreactor with moving bed carriers

A consortium of microalgae and nitrifiers has attracted attention as an alternative to the expensive traditional nitrification process. A possible obstacle to achieving this is the inhibition of nitrifiers under strong light irradiation. This study evaluated the effect of moving bed carriers on anaerobic digestate nitrification in an open photobioreactor inoculated with microalgae and nitrifiers under an incident light intensity of 1000 μmol photons m−2 s−1. The results showed higher specific nitrification activity in the carrier-added photobioreactor (103.6 mg-N g-TSS day−1) than in one in which no carrier was added (11.7 mg-N g-TSS day−1). The empirical equations for determining the light intensity at different depths in the photobioreactor showed a significant contribution by carriers in attenuating the incident light intensity. This is due to the large light attenuation caused by the carrier (1.09 cm−1). The average light intensity inside of the photobioreactor decreased considerably in the carrier-added photobioreactor (342 μmol photons m−2 s−1), whereas it did not decrease in the one with no added carrier. It was found that specific nitrification activity was significantly negatively affected by average light intensity inside of the reactor, and not by incident light intensity, by combining the results from different studies including ours. This study demonstrated, for the first time, the effectiveness of adding moving bed carriers in photobioreactors to mitigate light inhibition of nitrifiers in a consortium of microalgae and nitrifiers.

Light regulates inorganic nitrogen uptake and storage, but not nitrate assimilation, by the red macroalga Hemineura frondosa (Rhodophyta)

ABSTRACT Macroalgal growth in temperate coastal ecosystems is primarily regulated by light and inorganic nitrogen availability. The effect of light (photon irradiance) on NO3 − and NH4 + uptake, and NO3 − assimilation, were studied in the red macroalga, Hemineura frondosa, which does not operate a carbon concentrating mechanism (non-CCM). Non-CCM macroalgae grow in low and high light environments but become increasingly dominant with depth, suggesting a mechanism for ‘preserving energy’ under low light levels. H. frondosa was acclimated to limiting (30 µmol photons m− 2 s− 1) and saturating (150 µmol photons m− 2 s–1) irradiances for 8 days. Then, NO3 − and NH4 + uptake rates were measured under limiting and saturating irradiances at six concentrations ranging from 2–64 μM. NO3 − uptake did not follow saturating uptake kinetics at both irradiances suggesting multiple uptake mechanisms. NH4 + uptake saturated at concentrations <32 µM under limiting but not under saturating irradiance. Saturating irradiance resulted in greater maximum uptake rates of both NO3 − and NH4 +. There was no evidence that irradiance regulated NO3 − reduction by nitrate reductase. Also illustrated is the importance of measuring nitrate reductase activity on fresh material, as freezing in liquid nitrogen and storage at −80°C for 7 days caused a 65% decline in activity. Photosynthetic pigments, soluble tissue nitrogen and % total tissue nitrogen were all higher in limiting irradiance. In this first study of the nitrogen physiology of a non-CCM seaweed, we show that light regulates NO3 − and NH4 + uptake but not NO3 − assimilation.

Addition of carbon dioxide, followed by irradiance increase, as optimization strategy for the cultivation of the red seaweed Kappaphycus alvarezii

This work aimed to verify the effects of adding CO2 and irradiance to Kappaphycus alvarezii cultivation. Thalli were cultured in vitro for 2 weeks under low irradiance (50 μmol photons m−2 s−1) with the addition of CO2 according to the following concentrations: 142× 103 ppm (1CO2, 0.1 L min−1), 285 × 103 ppm (2CO2, 0.2 L min−1) and 428 × 103 ppm (3CO2, 0.3 L min−1), followed by culture under higher irradiance (200 μmol photons m−2 s−1) for 2 more weeks. Control had no CO2 addition. Afterwards, growth rate, chlorophyll a and carotenoid content were quantified. Samples were submitted to light microscopy and transmission electron microscopy. Growth rates of different treatments or control between experimental periods showed no significant differences, except for 2CO2 treatment at the end of each period. Kappaphycus alvarezii cultivated with CO2 addition showed cell wall thickening and increasing quantity of starch granules, chlorophyll a and carotenoids compared with control. Exposed to high irradiance, control samples showed signs of stress, such as changes in chloroplast, starch granules quantity decrease and total chlorophyll a and carotenoids increase. Samples cultivated with CO2 showed an increase in the quantity and size of the starch granules and an increase in the number of organelles (mitochondria) related to energy generation and cell construction (Golgi complex). Such alterations suggest cellular response after CO2 addition, such as the formation of starch reserves and cell wall thickening, which could make plants more tolerant to environmental stress during transport from indoor condition to sea farms.

Dunaliella sp. ABRIINW-I1 as a cell factory of nutraceutical fatty acid pattern: An optimization approach to improved production of docosahexaenoic acid (DHA)

The present study aimed to develop a culturing regime directed to achieve an optimal balance of growth with DHA yield by an indigenous DHA producing microalga, Dunaliella sp. ABRIINW-I1. An experimental factorial design with three factors of salinity, temperature, and light each in two levels of 0.5 and 2 M; 15 and 25 ℃, 200 and 1200 μmol photon m−2 s−1 was set up. The results showed that the combinatory effect of salinity, temperature and light was significant on biomass, total fatty acid (TFA) and DHA production. The highest biomass concentration was attained in 0.5 M, 25 ℃, 200 μmol photon m−2 s−1 (604 mg L−1) followed by 0.5 M, 25 ℃, 1200 μmol photon m−2 s−1 (574 mg L−1). The maximal DHA content of 36 % TFA and volumetric production of 30 mg L-1 occurred in 0.5 M, 25 ℃, 1200 μmol photon m−2 s-1. The achieved DHA level of Dunaliella sp. ABRIINW-I1 in its favorable production regime was comparable with those in commercial sources of Thraustochytrids. The studied microalga, generally, due to the high content of DHA, alpha-linolenic acid, n3:n6 ratio and proper lipid health indices might be nominated as a promising biofactory of fatty acids with nutritional value.

Extending the Library of Light‐Dependent Protochlorophyllide Oxidoreductases and their Solvent Tolerance, Stability in Light and Cofactor Flexibility

AbstractBiocatalysis is increasingly used in combination with light to develop new and more sustainable synthetic methods. Thereby, mostly a chemical photocatalyst harvesting the light energy is combined with an established enzymatic reaction, thus the biocatalyst itself does not require the light for its specific reaction. Here we expand the library of an enzyme which requires light for its natural reaction, namely the light‐dependent protochlorophyllide oxidoreductase (LPOR). This enzyme catalyzes the NADPH‐dependent reduction of a C=C in a N‐heterocycle. Out of five LPORs identified by sequence search, four were found to be well expressible in E. coli and active. Investigating the light intensity, which is an important parameter describing energy input and subsequently may enable fast reaction, it turned out that the four LPORs can stand the maximum light intensity reachable with the equipment used (1450 μmol photons m−2 s−1). However, the natural substrate and product were degraded at these conditions, allowing only 15 % of the maximum input (211 μmol photons m−2 s−1). Furthermore, the LPORs accepted seven different water miscible solvents with a solvent content of up to 20 % v/v and were active at a pH from 6 to 10. While all LPORs known to date are exclusively NADPH dependent, two LPORs identified here were active also with NADH. The cofactor selectivity could be pinned to three amino acid residues, which interestingly do not directly bind to the cofactor.

Production of carbohydrates, lipids and polyunsaturated fatty acids (PUFA) by the polar marine microalga Chlamydomonas malina RCC2488

Polar microalgae that are highly productive in cold climates can produce large amounts of biomass and polyunsaturated fatty acids (PUFA). The polar Chlamydomonas malina RCC2488, grows at low temperatures and produces high amounts of lipids, which are mainly composed of PUFA. However, not much is known about its phylogenetic relationship with other strains within the order Chlamydomonadales and the optimum growth conditions for maximum biomass productivity have not yet been identified. In this study, a phylogenetic analysis was performed to determine the closest relatives of C. malina within the Chlamydomonadales order. To select the best growth conditions for maximum biomass productivities in cultivations performed at 8 °C, different salinities (0–80) and light intensities (70–500 μmol photons m−2 s−1) were tested, using bubble column and flat-panel photobioreactors. The effect of nitrogen limitation was tested to determine if C. malina can accumulate energy reserve metabolites (carbohydrates and lipids). Phylogenetic analysis confirmed that C. malina, which belongs to the Chlamydomonales order, is closely related to the psychrophilics Chlamydomonas sp. UWO 241 and Chlamydomonas sp. SAG 75.94, as well as to the mesophilic C. parkeae MBIC 10599. The highest biomass (527 mg L−1 day−1), lipid (161.3 mg L−1 day−1) and polyunsaturated fatty acids (PUFA; 85.4 mg L−1 day−1) productivities were obtained at a salinity of 17.5, light intensity of 250 μmol photons m−2 s−1 and nitrogen replete conditions. Strikingly, the marine C. malina can grow even in fresh water, but the biomass productivity was reduced. While the intracellular lipid content remained unchanged under nitrogen deprivation, the carbohydrate content increased (up to 49.5% w/w), and the protein content decreased. The algal lipids were mainly comprised of neutral lipids, which were primarily composed of PUFA. Chlamydomonas malina RCC2488 is a polar marine microalga suitable for high biomass, carbohydrate, lipid and PUFA productivities at low temperatures.

Characterization of cyanobacterial allophycocyanins absorbing far-red light.

Phycobiliproteins (PBPs) are pigment proteins that comprise phycobilisomes (PBS), major light-harvesting antenna complexes of cyanobacteria and red algae. PBS core substructures are made up of allophycocyanins (APs), a subfamily of PBPs. Five paralogous AP subunits are encoded by the Far-Red Light Photoacclimation (FaRLiP) gene cluster, which is transcriptionally activated in cells grown in far-red light (FRL; λ = 700 to 800nm). FaRLiP gene expression enables some terrestrial cyanobacteria to remodel their PBS and photosystems and perform oxygenic photosynthesis in far-red light (FRL). Paralogous AP genes encoding a putative, FRL-absorbing AP (FRL-AP) are also found in an operon associated with improved low-light growth (LL; < 50μmol photons m-2s-1) in some thermophilic Synechococcus spp., a phenomenon termed low-light photoacclimation (LoLiP). In this study, apc genes from FaRLiP and LoLiP gene clusters were heterologously expressed individually and in combinations in Escherichia coli. The resulting novel FRL-APs were characterized and identified as major contributors to the FRL absorbance observed in whole cells after FaRLiP and potentially LoLiP. Post-translational modifications of native FRL-APs from FaRLiP cyanobacterium, Leptolyngbya sp. strain JSC-1, were analyzed by mass spectrometry. The PBP complexes made in two FaRLiP organisms were compared, revealing strain-specific diversity in the FaRLiP responses of cyanobacteria. Through analyses of native and recombinant proteins, we improved our understanding of how different cyanobacterial strains utilize specialized APs to acclimate to FRL and LL. We discuss some insights into structural changes that may allow these APs to absorb longer light wavelengths than their visible-light-absorbing paralogs.

Comparison of the Photoautotrophic Growth Regimens of Chlorella sorokiniana in a Photobioreactor for Enhanced Biomass Productivity

Microalgae have a wide industrial potential because of their high metabolic diversity and plasticity. Selection of optimal cultivation methods is important to optimize multi-purpose microalgal biotechnologies. In this research, Chlorella sorokiniana AM-02 that was isolated from a freshwater lake was cultured under various high photosynthetic photon flux density (PPFD) conditions and CO2 gas levels in standard Bold’s basal medium (BBM). Furthermore, a wide range of nitrate levels (180–1440 mg L−1) was tested on the growth of C. sorokiniana. Microalgae growth, pigment concentration, medium pH, exit gas composition, as well as nitrate, phosphate, and sulfate levels were measured during an experimental period. The preferred high PPFD and optimal CO2 levels were found to be 1000–1400 μmol photons m−2 s−1 and 0.5–2.0% (v/v), respectively. The addition of nitrate ions (up to 1440 mg L−1) to the standard growth medium increased final optical density (OD750), cell count, pigment concentration, and total biomass yield but decreased the initial growth rate at high nitrate levels. Our findings can serve as the basis for a robust photoautotrophic cultivation system to maximize the productivity of large-scale microalgal cultures.

Elevated Levels of Specific Carotenoids During Acclimation to Strong Light Protect the Repair of Photosystem II in Synechocystis sp. PCC 6803.

The tolerance of photosynthesis to strong light increases in photosynthetic organisms during acclimation to strong light. We investigated the role of carotenoids in the protection of photosystem II (PSII) from photoinhibition after acclimation to strong light in the cyanobacterium Synechocystis sp. PCC 6803. In cells that had been grown under strong light at 1,000 μmol photons m−2 s−1 (SL), specific carotenoids, namely, zeaxanthin, echinenone, and myxoxanthophyll, accumulated at high levels, and the photoinhibition of PSII was less marked than in cells that had been grown under standard growth light at 70 μmol photons m−2 s−1 (GL). The rate of photodamage to PSII, as monitored in the presence of lincomycin, did not differ between cells grown under SL and GL, suggesting that the mitigation of photoinhibition after acclimation to SL might be attributable to the enhanced ability to repair PSII. When cells grown under GL were transferred to SL, the mitigation of photoinhibition of PSII occurred in two distinct stages: a first stage that lasted 4 h and the second stage that occurred after 8 h. During the second stage, the accumulation of specific carotenoids was detected, together with enhanced synthesis de novo of proteins that are required for the repair of PSII, such as the D1 protein, and suppression of the production of singlet oxygen (1O2). In the ΔcrtRΔcrtO mutant of Synechocystis, which lacks zeaxanthin, echinenone, and myxoxanthophyll, the mitigation of photoinhibition of PSII, the enhancement of protein synthesis, and the suppression of production of 1O2 were significantly impaired during the second stage of acclimation. Thus, elevated levels of the specific carotenoids during acclimation to strong light appeared to protect protein synthesis from 1O2, with the resultant mitigation of photoinhibition of PSII.

UVA/persulfate-driven nonylphenol polyethoxylate degradation: effect of process conditions

ABSTRACT UV/persulfate (UV/PS) technologies have gained increased attention as efficient alternatives for removing pollutants from different classes, although processes based on the UVA-driven (PS) activation have not yet been discussed in the literature for the removal of the nonionic surfactant nonylphenol polyethoxylate (NPEO). The present study investigated the simultaneous effect of the initial persulfate concentration ([PS]0) and specific photon emission rate (E P,0) on NPEO degradation by UVA/PS following a Doehlert experimental design. The results for [NPEO]0 = (4.65 ± 0.15) mg L−1 indicated more than 97.8% NPEO removal after 2 h, with pseudo first-order specific degradation rate (k obs) of 0.0320 min−1, for [PS]0 = 7.75 mmol L−1 and E P,0 = 0.437 μmol photons L−1 s−1. Under these conditions, NPEO half-life time was about 22 min, and the EC50-48 h (% v/v) values for Daphnia similis before and after treatment did not differ significantly. Higher values of E P,0 would influence NPEO removal for [PS]0 not higher than 8–10 mmol L−1, although lower degradation efficiencies were obtained with higher [NPEO]0 or real wastewater, except for longer reaction times. Additionally, UVA/PS showed to be efficient for tensoactivity removal, despite the negligible total organic carbon (TOC) removal achieved. Finally, UVC and UVA resulted in NPEO degradation higher than 96% and similar tensoactivity removals when UVA/PS was conducted under optimal conditions ([PS]0 = 10 mmol L−1; E P,0 = 0.324 μmol photons L−1 s−1), suggesting that UVA radiation available in solar light could be advantageously employed for NPEO removal at concentrations usually found in wastewater.

Light dependent accumulation of β-carotene enhances photo-acclimation of Euglena gracilis

Carotenoids are essential components of photosynthetic organisms including land plants, algae, cyanobacteria, and photosynthetic bacteria. Although the light-mediated regulation of carotenoid biosynthesis, including the light/dark cycle as well as the dependence of carotenoid biosynthesis–related gene translation on light wavelength, has been investigated in land plants, these aspects have not been studied in microalgae. Here, we investigated carotenoid biosynthesis in Euglena gracilis and found that zeaxanthin accumulates in the dark. The major carotenoid species in E. gracilis, namely β-carotene, neoxanthin, diadinoxanthin and diatoxanthin, accumulated corresponding to the duration of light irradiation under the light/dark cycle, although the translation of carotenoid biosynthesis genes hardly changed. Irradiation with either blue or red-light (3 μmol photons m−2 s−1) caused a 1.3-fold increase in β-carotene content compared with the dark control. Blue-light irradiation (300 μmol photons m−2 s−1) caused an increase in the cellular content of both zeaxanthin and all trans-diatoxanthin, and this increase was proportional to blue-light intensity. In addition, pre-irradiation with blue-light of 3 or 30 μmol photons m−2 s−1 enhanced the photosynthetic activity and tolerance to high-light stress. These findings suggest that the accumulation of β-carotene is regulated by the intensity of light, which may contribute to the acclimation of E. gracilis to the light environment in day night conditions.

Identification, biochemical composition and phycobiliproteins production of Chroococcidiopsis sp. from arid environment

Molecular and microscopic studies were performed to identify Chroococcidiopsis sp., an endolithic cyanobacterium, isolated from gypsum rocks of Atacama Desert (Chile). It was adapted to grow in mineral liquid medium, with 9 mM nitrate, bubbled with CO2-enriched air (2.5 % v/v), and continuously illuminated with a white light of 70 μmol photons m–2 s–1. The obtained biomass (productivity of 0.21 g L–1 d–1) had a C/N ratio of 6.67, and it contained carbohydrates (45.40 % of dry weight), proteins (36.72 %), lipids (5.60 %) nucleic acids (3.90 %) and ashes (8.28 %). The lipid fraction was particularly rich in palmitic (29.86 % of total fatty acids), linoleic (18.20 %), palmitoleic (12.75 %), linolenic (10.92 %), stearic (9.64 %) and capric acid (6.29 %). Chroococcidiopsis sp. accumulated phycobiliproteins in a light-dependent process and produced 204 mg g–1, under incident light of 10 μmol photons·m–2·s–1, with a relative abundance of 40.9 % for phycocyanin, 23.3 % for phycoerythrin, and 35.8 % for allophycocyanin. The biomass from this cyanobacterium can be a good source of these pigments, especially APC (maximum of 95 mg g dw−1), which are of interest for pharmacological, cosmetic, and food industries.

Effect of light and temperature on photosynthesis of a cultivated brown alga, Saccharina sculpera (Laminariales), from Japan

ABSTRACT Understanding the physiological responses of kelp to environmental parameters is essential for the conservation of natural kelp beds and increased cultivation yield. We investigated the effects of photosynthetically active radiation (PAR) and temperature on photosynthesis of a subarctic edible brown alga, Saccharina sculpera (Laminariales), using pulse amplitude modulation (PAM)–chlorophyll fluorometry and optical dissolved oxygen sensors. Photosynthesis–PAR experiments at 8 °C, 15 °C, and 22 °C revealed the highest net photosynthetic rates at 22 °C. Values for compensation (Ec) and saturation (Ek) indicated a high affinity for a light environment that reflected the natural vertical habitat of this alga. The photosynthetic response of S. sculpera to temperature indicated that the optimum temperature for oxygenic photosynthesis () was 22.9 °C, which was consistent with the highest seawater temperature in Japanese distribution range for this subarctic species. The alga survived for 168 h at 24 °C in darkness. Continuous 6 h exposure to PAR of 100 µmol (low) and 1000 µmol (high) photons m–2 s–1 at 8 °C, 15 °C, and 22 °C induced chronic photoinhibition in the alga, with greater declines in effective quantum yields of photosystem II (ΦPSII). Failure to recover Fv/Fm after dark acclimation at low and high PAR was observed, except for low PAR at 8 °C. The physiological performance of S. sculpera indicates an affinity for a low light environment. We expect that our results will lead to an improvement in aquaculture techniques through the regulation of cultivation depth.