Inhibitory effects of hypo-osmotic stress on extracellular carbonic anhydrase and photosynthetic efficiency of green alga Dunaliella salina possibly through reactive oxygen species formation

Antibiotic occurrence, environmental risks, and their removal from aquatic environments using microalgae: Advances and future perspectives

Antibiotic pollution has caused a continuous increase in the development of antibiotic-resistant bacteria and antibiotic-resistant genes (ARGs) in aquatic environments worldwide. Algae-based bioremediation technology is a promising eco-friendly means to remove antibiotics and highly resistant ARGs, and the generated biomass can be utilized to produce value-added products of industrial significance. This review discussed the prevalence of antibiotics and ARGs in aquatic environments and their environmental risks to non-target organisms. The potential of various microalgal species for antibiotic and ARG removal, their mechanisms, strategies for enhanced removal, and future directions were reviewed. Antibiotics can be degraded into non-toxic compounds in microalgal cells through the action of extracellular polymeric substances, glutathione-S-transferase, and cytochrome P450; however, antibiotic stress can alter microalgal gene expression and growth. This review also deciphered the effect of antibiotic stress on microalgal physiology, biomass production, and biochemical composition that can impact their commercial applications.

Influence of salinity and temperature on the growth, productivity, photosynthetic activity and intracellular ROS of two marine microalgae and cyanobacteria

Global Climate Change could change physical parameters in oceans, such as salinity and temperature. The impact of such changes in phytoplankton has not been well stated yet. In this study the effect of combination of three levels of temperature (20, 23, and 26 °C), and three levels of salinity (33, 36, and 39) on growth of a mixture co-cultivation of three common species from phytoplankton (one cyanobacteria, Synechococcus sp., and two microalgae, Chaetoceros gracilis, and Rhodomonas baltica), is monitored by flow cytometry under controlled cultivation conditions in a 96 h study. Chlorophyll content, enzymes activities and oxidative stress were also measured. Results demonstrate that cultures of Synechococcus sp. Exhibited a high growth at the highest temperature chosen in this study (26 °C) combined with the three selected salinity levels 33, 36, and 39. Nevertheless, Chaetoceros gracilis grew very slowly with the combination of high temperature (39 °C) and all salinities, while Rhodomonas baltica did not grow at temperatures higher than 23 °C. Maximum dry biomass and ash-free dry weight for the microalgal mixture were reached at salinity of 39 and temperature of 20 °C, the but highest chlorophyll fluorescence values were found at 30 salinity and 20 °C, decreasing as salinity and temperature increased.

Salinity fluctuation influences the toxicity of 1-octyl-3-methylimidazolium chloride ([C8mim]Cl) to a marine diatom Phaeodactylum tricornutum

In this work, a marine diatom (Phaeodactylum tricornutum) was exposed to 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl) for 96 h at three different salinities (25, 35, and 45 ‰) for investigating their interactive effects. Results showed that values of EC₁₀ and EC₅₀ at 96 h of exposure were 0.29, 1.06, 2.01 μg L^-1 and 7.21, 7.71, 7.25 mg L^-1 when the salinities were 25, 35, and 45 ‰, respectively, meaning that salinity fluctuation affected the toxicity of [C₈mim]Cl to this diatom. Changes in chlorophyll a contents and chlorophyll fluorescence parameters suggested that [C₈mim]Cl and salinity fluctuation had a significant interactive effect on the algal photosynthesis. In addition, soluble protein content and activities of antioxidant enzymes in algal cells changed significantly. Increased malondialdehyde contents indicated that the combined stresses could induce excessive production of reactive oxygen species leading to oxidative damage to the algal cells.

A two-stage degradation coupling photocatalysis to microalgae enhances the mineralization of enrofloxacin

The coupling of photocatalytic and algal processes has been used for the removal of widespread antibiotics. The removal capacities of the individual and the combined system against enrofloxacin were tested and compared in this work. Due to the low tolerance of the algae to enrofloxacin, the target compound was barely degraded during the individual algal treatment. In the individual photocatalytic process, the mineralization efficiency (defined as the ratio between the produced carbon dioxide and the initial) reached ∼57% with the remaining formed as transformation products. In contrast, a two-stage treatment incorporating photocatalytic and algal processes removed enrofloxacin completely and increased the mineralization efficiency to ∼64% or more. The addition of the citric acid as external co-substrate further elevated the mineralization efficiency with a factor of 1.25 compared to that of the individual photocatalysis. Different degradation products in both individual and integrated processes were identified and compared. The degradation pathways were found to involve the attack of the piperazine moiety and quinolone core. The results indicated the potential application of the combined photocatalytic-algal treatment in removal of veterinary antibiotics and improved our understanding of the underlying mechanisms and pathways.

The response of three typical freshwater algae to acute acid stress in water

The effect of acidic pH conditions on the physiological response of three typical freshwater algae, Chlorella vulgaris, Microcystis aeruginosa and Scenedesmus quadricauda, was investigated in this study. The results of the cultivation experiment indicated that the mortality of the three algae in the logarithmic growth phase increased with increasing exposure time and acidity under acute acidic conditions. The tolerance of S. quadricauda was stronger than that of the other two species under long-term (6 h) exposure to the same acidity; in contrast, C. vulgaris exhibited the greatest tolerance under short-term exposure conditions. The decrease in chlorophyll a (Chl a) content indicated that the photosynthesis of algae was inhibited under acid stress and that the algae could not continue to grow normally. This was consistent with the changes in lipid peroxidation and antioxidant enzyme activity, which were reflected by the malondialdehyde (MDA) content and superoxide dismutase (SOD) activity under acid stress, respectively. The results of this study demonstrated that when exposed to acute acidic conditions, the tolerance of three typical freshwater algae to acidity was significantly different. These findings provide valuable information for poorly mixed acidification operations designed to adjust the pH in lakes, reservoirs, or intake pipes of purification plants.

Selenite as a Lipid Inductor in Marine Microalga Dunaliella tertiolecta: Comparison of One-Stage and Two-Stage Cultivation Strategies

Microalgae have emerged as one of the most promising alternative sources of biofuels due to their high lipid accumulation ability. High lipid content is of pivotal importance for biodiesel production. In order to obtain high lipid content, modifications of culture conditions and development of an efficient lipid induction method are called for. In the present study, the possibility of using selenium in a form of sodium selenite as a lipid inductor in marine microalga Dunaliella tertiolecta was investigated during one- and two-stage cultivation modes. The effects of selenite on algal growth, pigment content, oxidative stress, and neutral lipid content were determined during both cultivation modes. The results revealed that the two-stage cultivation on 10.00-40.00 mg L^-1 of selenite resulted in up to twofold higher algal cell density compared to the one-stage cultivation. Selenite concentrations from 2.50 to 20.00 mg L^-1 increased lipid peroxidation during both cultivation modes, emphasizing the selenite-induced oxidative stress accompanied by the increased lipid accumulation in microalgae cells. During one- and two-stage cultivation on 20.00 mg L^-1 of selenite, lipid content increased 2.39- and 5.73-fold at days 9 and 14 of cultivation, respectively. Moreover, the highest obtained neutral lipid content during the two-stage cultivation was 5.40-fold higher than lipid content obtained during the one-stage cultivation. Collectively, these results suggest that the two-stage cultivation strategy, initiated with optimal culture conditions for biomass production and followed by the addition of selenite as a stress inductor, can be successfully deployed to enhance the lipid content in D. tertiolecta.

Comparative Transcriptome Analysis Provides Insights into Response of Ulva compressa to Fluctuating Salinity Conditions

Ulva compressa, a green tide-forming species, can adapt to hypo-salinity conditions, such as estuaries and brackish lakes. To understand the underlying molecular mechanisms of hypo-salinity stress tolerance, transcriptome-wide gene expression profiles in U. compressa were created using digital gene expression profiles. The RNA-seq data were analyzed based on the comparison of differently expressed genes involved in specific pathways under hypo-salinity and recovery conditions. The up-regulation of genes in photosynthesis and glycolysis pathways may contribute to the recovery of photosynthesis and energy metabolism, which could provide sufficient energy for the tolerance under long-term hyposaline stress. Multiple strategies, such as ion transportation and osmolytes metabolism, were performed to maintain the osmotic homeostasis. Additionally, several long noncoding RNA were differently expressed during the stress, which could play important roles in the osmotolerance. Our work will serve as an essential foundation for the understanding of the tolerance mechanism of U. compressa under the fluctuating salinity conditions.

Stress-Related Changes in the Expression and Activity of Plant Carbonic Anhydrases

The data on stress-related changes in the expression and activity of plant carbonic anhydrases (CAs) suggest that they are generally upregulated at moderate stress severity. This indicates probable involvement of CAs in adaptation to drought, high salinity, heat, high light, C_i deficit, and excess bicarbonate. The changes in CA levels under cold stress are less studied and generally represented by the downregulation of CAs excepting βCA2. Excess Cd²⁺ and deficit of Zn²⁺ specifically reduce CA activity and reduce its synthesis. Probable roles of βCAs in stress adaptation include stomatal closure, ROS scavenging and partial compensation for decreased mesophyll CO₂ conductance. βCAs play contrasting roles in pathogen responses, interacting with phytohormone signaling networks. Their role can be either negative or positive, probably depending on the host-pathogen system, pathogen initial titer, and levels of ·NO and ROS. It is still not clear why CAs are suppressed under severe stress levels. It should be noted, that the role of βCAs in the facilitation of CO₂ diffusion and their involvement in redox signaling or ROS detoxication are potentially antagonistic, as they are inactivated by oxidation or nitrosylation. Interestingly, some chloroplastic βCAs may be relocated to the cytoplasm under stress conditions, but the physiological meaning of this effect remains to be studied.

ROS Induce β-Carotene Biosynthesis Caused by Changes of Photosynthesis Efficiency and Energy Metabolism in Dunaliella salina Under Stress Conditions

The unicellular alga Dunaliella salina is regarded as a promising cell factory for the commercial production of β-carotene due to its high yield of carotenoids. However, the underlying mechanism of β-carotene accumulation is still unclear. In this study, the regulatory mechanism of β-carotene accumulation in D. salina under stress conditions was investigated. Our results indicated that there is a significant positive correlation between the cellular ROS level and β-carotene content, and the maximum quantum efficiency (F_v/F_m) of PSII is negatively correlated with β-carotene content under stress conditions. The increase of ROS was found to be coupled with the inhibition of F_v/F_m of PSII in D. salina under stress conditions. Furthermore, transcriptomic analysis of the cells cultivated with H₂O₂ supplementation showed that the major differentially expressed genes involved in β-carotene metabolism were upregulated, whereas the genes involved in photosynthesis were downregulated. These results indicated that ROS induce β-carotene accumulation in D. salina through fine-tuning genes which were involved in photosynthesis and β-carotene biosynthesis. Our study provided a better understanding of the regulatory mechanism involved in β-carotene accumulation in D. salina, which might be useful for overaccumulation of carotenoids and other valuable compounds in other microalgae.

The effects of exogenous cerium on photosystem II as probed by in vivo chlorophyll fluorescence and lipid production of Scenedesmus obliquus XJ002

Cerium is the most abundant rare earth metal in the earth's crust, and it has deleterious effects on aquatic ecosystems from fertilizer runoff. Scenedesmus obliquus is an oil-rich microalga that grows rapidly and is sensitive to many kinds of toxins. Given that microalgae are useful indicators of eutrophication and toxic stress, it was found that lower concentrations of cerium (0.50-5.00 mg·L^-1 ) stimulated algal growth and increased chlorophyll a content, whereas higher concentrations (above 50.00 mg·L^-1 ) had an inhibitory effect on algal growth and chlorophyll a content. The algal growth rate and chlorophyll a content peaked at a cerium concentration of 5.00 mg·L^-1 . Both the donor and acceptor sides of photosystem II (PSII) reaction centers were sensitive to cerium-induced stress. Specifically, high concentrations of cerium damaged the oxygen evolving complex and PSII reaction center and suppressed electron transport at the donor and receptor side of the reaction center, influencing the absorption, transfer, and application of light energy in S. obliquus XJ002. In addition, we established a simple method to quantify the intracellular lipid content of S. obliquus XJ002, and the optimum staining conditions for Nile red were as follows: volume percentage of dimethyl sulfoxide was 2%, the concentration of Nile red was 2.0 µg·mL^-1 , and the staining time of Nile red was 5 min. The addition of cerium resulted in a significant increase in the total lipid content of XJ002. When the concentration of cerium was 50 mg·L^-1 , the total lipid content was 16.26% higher than the control group. This information will enhance our ability to utilize microelement fertilizer in biomass accumulation programs and will help to further reveal the key regulatory factors in the lipid metabolism, and would lay the foundation for promoting the research of microalgae bioenergy.

Ecotoxicological effects of sulfonamides and fluoroquinolones and their removal by a green alga (Chlorella vulgaris) and a cyanobacterium (Chrysosporum ovalisporum)

In recent years, antibiotic pollution has become worse, especially in China. In this study, the ecotoxicological effects of four frequently used antibiotics with different lipophilic degrees (log Kow) (sulfadiazine (SD), sulfamethazine (SM2), enrofloxacin (ENR), and norfloxacin (NOR)) at four concentrations of 1, 5, 20, and 50 mg L^-1 were examined using batch cultures of green alga Chlorella vulgaris and cyanobacterium Chrysosporum ovalisporum for 16 days based on changes in chlorophyll fluorescence parameters (chl a, Fv/Fm, and ΦPSII) and responses of the antioxidant system. Besides, the antibiotics removal efficiencies of the two microalgae were investigated. Sulfonamides (SD and SM2) had no significant inhibitory effect on the growth of C. ovalisporum, but had an inhibitory effect on C. vulgaris, whereas fluoroquinolones (ENR and NOR) significantly inhibited C. ovalisporum. The activities of superoxide dismutase, catalase, and glutathione reductase suggested that C. vulgaris was more tolerant to these antibiotics than C. ovalisporum. The increased malondialdehyde level in both algae indicated their tolerance against antibiotics. When compared with C. ovalisporum, C. vulgaris presented better capacity to remove antibiotics. In summary, the four antibiotics exerted time- or concentration-dependent ecotoxicological effects on the microalgae examined, whereas the microalgae could remove the antibiotics based on the log Kow of the antibiotics. The findings of this study contribute to effective understanding of the ecotoxicological effects of antibiotics and their removal by microalgae.

β-Carotene Production from Dunaliella salina Cultivated with Bicarbonate as Carbon Source

Bicarbonate has been considered as a better approach for supplying CO₂ to microalgae cells microenvironments than gas bubbling owing t°Cost-effectiveness and easy operation. However, the β-carotene production was too low in Dunaliella salina cultivated with bicarbonate in previous studies. Also, the difference in photosynthetic efficiency between these tw°Carbon sources (bicarbonate and CO₂) has seldom been discussed. In this study, the culture conditions, including NaHCO₃, Ca²⁺, Mg²⁺ and microelement concentrations, were optimized when bicarbonate was used as carbon source. Under optimized condition, a maximum biomass concentration of 0.71 g/l and corresponding β-carotene content of 4.76% were obtained, with β-carotene yield of 32.0 mg/l, much higher than previous studies with NaHCO₃. Finally, these optimized conditions with bicarbonate were compared with CO₂ bubbling by online monitoring. There was a notable difference in F_v/F_m value between cultivations with bicarbonate and CO₂, but there was no difference in the F_v/F_m periodic changing patterns. This indicates that the high concentration of NaHCO₃ used in this study served as a stress factor for β-carotene accumulation, although high productivity of biomass was still obtained.

Responses of the kelp Saccharina latissima (Phaeophyceae) to the warming Arctic: from physiology to transcriptomics

The Arctic region is currently facing substantial environmental changes due to global warming. Melting glaciers cause reduced salinity environments in coastal Arctic habitats, which may be stressful for kelp beds. To investigate the responses of the kelp Saccharina latissima to the warming Arctic, we studied the transcriptomic changes of S. latissima from Kongsfjorden (Svalbard, Norway) over a 24-hour exposure to two salinities (Absolute Salinity [SA ] 20 and 30) after a 7-day pre-acclimation at three temperatures (0, 8 and 15°C). In addition, corresponding physiological data were assessed during an 11-days salinity/temperature experiment. Growth and maximal quantum yield for photosystem II fluorescence were positively affected by increased temperature during acclimation, whereas hyposalinity caused negative effects at the last day of treatment. In contrast, hyposalinity induced marked changes on the transcriptomic level. Compared to the control (8°C - SA 30), the 8°C - SA 20 exhibited the highest number of differentially expressed genes (DEGs), followed by the 0°C - SA 20. Comparisons indicate that S. latissima tends to convert its energy from primary metabolism (e.g. photosynthesis) to antioxidant activity under hyposaline stress. The increase in physiological performance at 15°C shows that S. latissima in the Arctic region can adjust and might even benefit from increased temperatures. However, in Arctic fjord environments its performance might become impaired by decreased salinity as a result of ice melting.

Exploring the potency of integrating semi-batch operation into lipid yield performance of Chlamydomonas sp. Tai-03

Third generation biofuels, also known as microalgal biofuels, are promising alternatives to fossil fuels. One attractive option is microalgal biodiesel as a replacement for diesel fuel. Chlamydomonas sp. Tai-03 was previously optimized for maximal lipid production for biodiesel generation, achieving biomass growth and productivity of 3.48 ± 0.04 g/L and 0.43 ± 0.01 g/L/d, with lipid content and productivity of 28.6 ± 1.41% and 124.1 ± 7.57 mg/L/d. In this study, further optimization using 5% CO₂ concentration and semi-batch operation with 25% medium replacement ratio, enhanced the biomass growth and productivity to 4.15 ± 0.12 g/L and 1.23 ± 0.02 g/L/d, with lipid content and productivity of 19.4 ± 2.0% and 239.6 ± 24.8 mg/L/d. The major fatty acid methyl esters (FAMEs) were palmitic acid (C16:0), oleic acid (C18:1), and linoleic acid (C18:2). These short-chain FAMEs combined with high growth make Chlamydomonas sp. Tai-03 a suitable candidate for biodiesel synthesis.

Effect of Bisphenol A on the extremophilic microalgal strain Picocystis sp. (Chlorophyta) and its high BPA removal ability

Bisphenol A (BPA) effects and removal by an alkaliphilic chlorophyta, Picocystis, were assessed. BPA at low concentrations (0-25 mg L^-1) did not inhibit the Picocystis growth and photosynthesis during 5 days of exposure. At higher BPA concentrations (50 and 75 mg L^-1), the growth inhibition did not exceed 43%. The net photosynthetic activity was dramatically reduced at high BPA concentrations while, the PSII activity was less affected. The exposure to increasing BPA concentrations induced an oxidative stress in Picocystis cells, as evidenced by increased malondialdehyde content and the over-expression of antioxidant activities (ascorbate peroxydase, gluthation-S-transferase and catalase). Picocystis exhibited high BPA removal efficiency, reaching 72% and 40% at 25 and 75 mg L^-1 BPA. BPA removal was ensured mainly by biodegradation/biotransformation processes. Based on these results, the extended tolerance and the high removal ability of Picocystis make her a promising specie for use in BPA bioremediation.

The effect of NaCl stress on photosynthetic efficiency and lipid production in freshwater microalga-Scenedesmus obliquus XJ002

Rapid industrialization and population growth have increased the world's energy demands, resulting in a shortage of conventional fossil fuels. Thus, there is an urgent need to develop sustainable and renewable forms of energy. Microalgae have emerged as a potential feedstock for biofuel production. Under stress conditions, lipid production is enhanced in algal cells due to changes in the lipid biosynthetic pathways that produce neutral lipids. In this study, we examined the physiological and biochemical effects of salinity stress (0.00, 0.01, 0.10, 0.15, 0.20M) on the freshwater microalga Scenedesmus obliquus XJ002. We found that the biomass and the content of chlorophyll a, b and carotenoids decreased with increasing NaCl concentration. NaCl stress damaged the oxygen evolving complex (OEC) and the PSII (photosystem II) reaction center and subsequently suppressed electron transport at the donor and receptor sides of the reaction center, influencing the absorption, transfer, and application of light energy. Additionally, the total lipid content of cells was significantly increased under NaCl stress treatment. The highest lipid content (32.26%) was found in cells cultured in the presence of 0.20M NaCl, which was about 2.52-fold higher than that of cells grown in medium lacking NaCl (12.82%). In addition to providing insight into the physiological and biochemical responses of S. obliquus XJ002 to salinity stress, these findings show that lipid production, and hence biofuel feedstock production, can be boosted by adjusting salt levels in the growth medium.

Lipid productivity in limnetic Chlorella is doubled by seawater added with anaerobically digested effluent from kitchen waste

BACKGROUND

An economical strategy for producing microalgae as biofuel feedstock is driven by the freshwater and nutrients input. In this study, seawater was applied to limnetic algal cultivation and the behavior of algae in seawater media was observed including growth, lipid synthesis, and ultrastructure. To make seawater cater algae, a kind of wastewater, anaerobically digested effluent from kitchen waste (ADE-KW), was used as nutrient sources.

RESULTS

Pure seawater cannot support the growth demand of freshwater microalga, due to high salinity and lack of nutrients. However, it is the conditions triggered the algae to synthesize lipids of 60%, double of lipid content in standard medium BG11. Introducing 3 or 5% ADE-KW (volume percentage) into seawater made algal growth reach the level attained in BG11, while lipid content compared favourably with the level (60%) in pure seawater. This method achieved the goal of fast growth and lipid accumulation simultaneously with the highest lipid productivity (19 mg/L  day) at the exponential stage, while BG11 obtained 10.55 mg/L  day at the stationary stage as the highest lipid productivity, almost half of that in seawater media. Moreover, the condition for highest lipid productivity enlarged algal cells compared to BG11. Under the condition for highest lipid productivity, Chlorella sorokiniana SDEC-18 had enlarged cells and increased settling efficiency compared to BG11, which facilitated harvest in an energy saving way.

CONCLUSIONS

The results suggested that combining seawater with ADE-KW to cultivate microalgae had a double function: nutrients and water for algal growth, and high salinity for stimulating lipid accumulation. If this technology was operated in practice, freshwater and non-waste nutrient consumption would be completely obviated.

Salinity-induced cellular cross-talk in carbon partitioning reveals starch-to-lipid biosynthesis switching in low-starch freshwater algae

Salinity stress has been verified to be a successful approach to enhance lipid production in high-starch marine algae, and salinity-induced carbon flow switching has been proposed as an algal response specific to brackish water. With the aim of testing this assumption, Chlorella sorokiniana SDEC-18, a low-starch freshwater alga, was grown in BG11 medium with NaCl addition at various concentrations (0, 2, 5, 10, 20, and 30 g/L). The results showed that salinity stress promoted carbon redistribution and starch conversion to lipid. The most desirable lipid productivity of 19.66 mg/L·d occurred in the medium with 20 g/L NaCl, about 2.16 times as high as that in the BG11 medium control. Moreover, microalgae with salinity stress were able to produce biodiesel with a more suitable cloud point, due to a decrease in the saturated fatty acid content. This therefore confirms that low-starch freshwater microalgae can also carry out salinity-induced carbon flow switching.

Salinity induced oxidative stress alters the physiological responses and improves the biofuel potential of green microalgae Acutodesmus dimorphus

The main aim of the present study was to analyze salinity stress induced physiological and biochemical changes in a freshwater microalgae Acutodesmus dimorphus. During single-stage cultivation, the accumulations of lipids and carbohydrates increased with an increase in an initial salinity of the culture medium. The carbohydrate and lipid accumulations of 53.30±2.76% and 33.40±2.29%, respectively, were observed in 200mM NaCl added culture. During two-stage cultivation, salinity stress of 200mM was favorable for the growth up to 2days, as suggested by higher biomass, lower levels of oxidative stress biomarkers and no significant changes in the biochemical composition of the cells. Extending the stress to 3days significantly increased the lipid accumulation by 43% without affecting the biomass production. This study, thus, provides the strategy to improve the biofuel potential of A. dimorphus along with presenting the physiological adaptive mechanisms of a cell against salinity stress.

Cadmium effect on physiological responses of the tolerant Chlorophyta specie Picocystis sp. isolated from Tunisian wastewaters

This study aims to investigate the effects of different concentrations of cadmium (Cd) (0-800 μM) on the growth, the photosynthetic performance, and the biochemical parameters of the Chlorophyta Picocystis sp. during 3 and 9 days. Results showed that this exposure did not inhibit the Picocystis growth during the first 3 days of treatment. Growth inhibition did not exceed 53%, which was recorded at high Cd concentrations (800 μM) after nine exposure days. Moreover, no inhibitory effect on the Picocystis sp. photosynthesis has been recorded during the three exposure days regardless the Cd concentrations. Lipid peroxidation was significantly increased at high Cd concentrations (500 and 800 μM) by 40 and 80%, respectively. Furthermore, the highest Cd concentration enhanced the thiol protein content, indicating no consequent protein oxidation. The exposure of Picocystis to Cd stimulated the antioxidant activities of catalase and ascorbate peroxidase. These results showed that Picocystis sp. has an impressive tolerance to Cd stress.

Insights into the molecular mechanism of the responses for Cyperus alternifolius to PhACs stress in constructed wetlands

Cyperus alternifolius has been widely reported to be an effective phytoremediation plant in constructed wetland systems (CWs). In this context, an integrated biochemical and proteomic analysis of C. alternifolius leaves exposed to pharmaceutically active compounds (PhACs) in CWs was conducted to understand the mechanism of phytoremediation. The obtained results showed the antioxidant enzyme activities were induced throughout the experiment; however over time, the malondialdehyde content is not significantly different from the control and the photosynthetic pigment contents in plant were subsequently slowly recovered. Therefore, we concluded that reactive oxygen species could be effectively counteracted by the enhanced antioxidant enzyme activities, and therefore the photosynthetic pigments were ultimately restored. Leaf extract proteome maps were obtained through 2-DE, and an average of 55, 49, and 24 spots were significantly altered by 30, 100, and 500 μg/L of PhACs over the control, respectively. Protein expression patterns showed that proteins in C. alternifolius leaves are associated with photosynthesis, energy metabolism, defense, and protein synthesis. Moreover, the most relevant pathways modulated by PhACs were photosynthesis and energy metabolism. The protein expression involved in antioxidant defense and stress response generally increased in all the PhAC treatments. The regulated proteins may favor PhAC degradation in CWs; however, the role of these proteins in degrading PhACs remains unknown; further biochemical studies should be conducted. This study indicated that C. alternifolius can tolerate multiple PhACs.

Extracellular Metabolites from Industrial Microalgae and Their Biotechnological Potential

Industrial microalgae, as a big family of promising producers of renewable biomass feedstock, have been commercially exploited for functional food, living feed and feed additives, high-value chemicals in nutraceuticals, cosmeceuticals, and chemical reagents. Recently, microalgae have also been considered as a group that might play an important role in biofuel development and environmental protection. Almost all current products of industrial microalgae are derived from their biomass; however, large amounts of spent cell-free media are available from mass cultivation that is mostly unexploited. In this contribution we discuss that these media, which may contain a remarkable diversity of bioactive substances are worthy to be recovered for further use. Obviously, the extracellular metabolites from industrial microalgae have long been neglected in the development of production methods for valuable metabolites. With the advances in the last ten years, more and more structures and properties from extracellular metabolites have been identified, and the potential utilization over wide fields is attracting attention. Some of these extracellular metabolites can be potentially used as drugs, antioxidants, growth regulators or metal chelators. The purpose of this review is to provide an overview of the known extracellular metabolites from industrial microalgae which might be of commercial interest. The attention mainly focuses on the reports of extracellular bioactive metabolites and their potential application in biotechnology.

Is foliar spray of proline sufficient for mitigation of salt stress in Brassica juncea cultivars?

The effects of foliar application of proline (20 mM) on growth, physio-biochemical, and yield parameters were assessed in two Brassica juncea (L.) Czern & Coss cultivars, namely, Varuna and RH-30, at different levels (2.8, 4.2, or 5.6 dsm(-1)) of NaCl in soil. At 29 days after sowing (DAS), plants were sprayed with either 20 mM proline or water in the presence or absence of NaCl stress. The NaCl negatively affected parameters related to growth, photosynthesis, and yield in both varieties but more in RH-30 than in Varuna. Exogenous application of proline counteracted the effects of salt stress in Varuna only, by increasing the antioxidative capacity of the plants. Moreover, proline was not effective in alleviating the detrimental effects of higher salt concentrations on the studied parameters. Proline application to unstressed plants increased growth, photosynthesis, and yield parameters in both varieties; however, the effects were more prominent in Varuna than in RH-30.

Salinity induced oxidative stress enhanced biofuel production potential of microalgae Scenedesmus sp. CCNM 1077

Microalgal biomass is considered as potential feedstock for biofuel production. Enhancement of biomass, lipid and carbohydrate contents in microalgae is important for the commercialization of microalgal biofuels. In the present study, salinity stress induced physiological and biochemical changes in microalgae Scenedesmus sp. CCNM 1077 were studied. During single stage cultivation, 33.13% lipid and 35.91% carbohydrate content was found in 400 mM NaCl grown culture. During two stage cultivation, salinity stress of 400 mM for 3 days resulted in 24.77% lipid (containing 74.87% neutral lipid) along with higher biomass compared to single stage, making it an efficient strategy to enhance biofuel production potential of Scenedesmus sp. CCNM 1077. Apart from biochemical content, stress biomarkers like hydrogen peroxide, lipid peroxidation, ascorbate peroxidase, proline and mineral contents were also studied to understand the role of reactive oxygen species (ROS) mediated lipid accumulation in microalgae Scenedesmus sp. CCNM 1077.

Effects of abiotic stressors on lutein production in the green microalga Dunaliella salina

BACKGROUND

Recent years have witnessed a rising trend in exploring microalgae for valuable carotenoid products as the demand for lutein and many other carotenoids in global markets has increased significantly. In green microalgae lutein is a major carotenoid protecting cellular components from damage incurred by reactive oxygen species under stress conditions. In this study, we investigated the effects of abiotic stressors on lutein accumulation in a strain of the marine microalga D. salina which had been selected for growth under stress conditions of combined blue and red lights by adaptive laboratory evolution.

RESULTS

Nitrate concentration, salinity and light quality were selected as three representative influencing factors and their impact on lutein production in batch cultures of D. salina was evaluated using response surface analysis. D. salina was found to be more tolerant to hyper-osmotic stress than to hypo-osmotic stress which caused serious cell damage and death in a high proportion of cells while hyper-osmotic stress increased the average cell size of D. salina only slightly. Two models were developed to explain how lutein productivity depends on the stress factors and for predicting the optimal conditions for lutein productivity. Among the three stress variables for lutein production, stronger interactions were found between nitrate concentration and salinity than between light quality and the other two. The predicted optimal conditions for lutein production were close to the original conditions used for adaptive evolution of D. salina. This suggests that the conditions imposed during adaptive evolution may have selected for the growth optima arrived at.

CONCLUSIONS

This study shows that systematic evaluation of the relationship between abiotic environmental stresses and lutein biosynthesis can help to decipher the key parameters in obtaining high levels of lutein productivity in D. salina. This study may benefit future stress-driven adaptive laboratory evolution experiments and a strategy of applying stress in a step-wise manner can be suggested for a rational design of experiments.

Salt-induced modulation in growth, photosynthesis and antioxidant system in two varieties of Brassica juncea

The present study was carried out to examine salt-induced modulation in growth, photosynthetic characteristics and antioxidant system in two cultivars of Brassica juncea Czern and Coss varieties (Varuna and RH-30). The surface sterilized seeds of these varieties were sown in the soil amended with different levels (2.8, 4.2 or 5.6 dsm(-1)) of sodium chloride under a simple randomized block design. The salt treatment significantly decreased growth, net photosynthetic rate and its related attributes, chlorophyll fluorescence, SPAD value of chlorophyll, leaf carbonic anhydrase activity and leaf water potential, whereas electrolyte leakage, proline content, and activity of catalase, peroxidase and superoxide dismutase enzymes increased in both the varieties at 30 d stage of growth. The variety Varuna was found more resistant than RH-30 to the salt stress and possessed higher values for growth, photosynthetic attributes and antioxidant enzymes. Out of the graded concentrations (2.8, 4.2 or 5.6 dsm(-1)) of sodium chloride, 2.8 sm(-1) was least toxic and 5.6 dsm(-1) was most harmful. The variation in the responses of these two varieties to salt stress is attributed to their differential photosynthetic traits, SPAD chlorophyll value and antioxidant capacity, which can be used as potential markers for screening mustard plants for salt tolerance.