Green Alga Scenedesmus Obliquus Research Articles

Cadmium-Induced Physiological Responses, Biosorption and Bioaccumulation in Scenedesmus obliquus.

Cadmium ion (Cd2+) is a highly toxic metal in water, even at low concentrations. Microalgae are a promising material for heavy metal remediation. The present study investigated the effects of Cd2+ on growth, photosynthesis, antioxidant enzyme activities, cell morphology, and Cd2+ adsorption and accumulation capacity of the freshwater green alga Scenedesmus obliquus. Experiments were conducted by exposing S. obliquus to varying concentrations of Cd2+ for 96 h, assessing its tolerance and removal capacity towards Cd2+. The results showed that higher concentrations of Cd2+ (>0.5 mg L-1) reduced pigment content, inhibited algal growth and electron transfer in photosynthesis, and led to morphological changes such as mitochondrial disappearance and chloroplast deformation. In this process, S. obliquus counteracted Cd2+ toxicity by enhancing antioxidant enzyme activities, accumulating starch and high-density granules, and secreting extracellular polymeric substances. When the initial Cd2+ concentration was less than or equal to 0.5 mg L-1, S. obliquus was able to efficiently remove over 95% of Cd2+ from the environment through biosorption and bioaccumulation. However, when the initial Cd2+ concentration exceeded 0.5 mg L-1, the removal efficiency decreased slightly to about 70%, with biosorption accounting for more than 60% of this process, emerging as the predominant mechanism for Cd2+ removal. Fourier transform infrared correlation spectroscopy analysis indicated that the carboxyl and amino groups of the cell wall were the key factors in removing Cd2+. In conclusion, S. obliquus has considerable potential for the remediation of aquatic environments with Cd2+, providing algal resources for developing new microalgae-based bioremediation techniques for heavy metals.

Diet effects on longevity, heat tolerance, lipid peroxidation and mitochondrial membrane potential in Daphnia.

The dietary supply of polyunsaturated fatty acids (PUFA) crucially affects animals' performance at different temperatures. However, the underlying physiological mechanisms are still insufficiently understood. Here, we analyzed lifespan and heat tolerance of four genotypes of Daphnia magna reared on either the green alga Scenedesmus obliquus that lacks long-chain (> C18) PUFA, or the heterokont alga Nannochloropsis limnetica that contains C20 PUFA, both either at saturating and near-starvation levels. A significant genotype-by-diet interaction in lifespan was observed at saturating diets. The C20 PUFA-rich diet eliminated differences in lifespan among genotypes on the PUFA-deficient diet. Corrected for body length, acute heat tolerance was higher at low than at high food concentration, at least in the older of the two age groups analyzed. Genotypes differed significantly in heat tolerance, but there were no genotype-by-diet interactions. As predicted, the C20 PUFA-rich diet resulted in higher lipid peroxidation (LPO) and a lower mitochondrial membrane potential (ΔΨm). LPO levels averaged across clones and rearing conditions were inversely related to acute heat tolerance. Yet, heat tolerance was higher on the PUFA-rich diet than on the PUFA-deficient diet, particularly in older Daphnia, indicating that the C20 PUFA-rich diet allowed Daphnia to compensate for higher LPO. In contrast, Daphnia with intermediate levels of ΔΨm showed the lowest heat tolerance. Neither LPO nor ΔΨm explained the diet effects on lifespan. We hypothesize that antioxidants present in the PUFA-rich diet may have enabled higher heat tolerance of Daphnia despite higher LPO, which may also explain the lifespan expansion of otherwise short-lived genotypes.

Discovery of a High-Efficient Algicidal Bacterium against Microcystis aeruginosa Based on Examinations toward Culture Strains and Natural Bloom Samples.

Harmful cyanobacterial blooms occur worldwide and pose a great threat to aquatic ecosystems and public health. The application of algicidal bacteria represents an eco-friendly strategy for controlling harmful cyanobacterial blooms; thus, searching for a high efficiency of algicidal bacteria has been becoming an important and continuous task in science. Herein, we identified a bacterial strain coded Streptomyces sp. HY with a highly algicidal activity, and investigated its algicidal efficiency and mechanism against Microcystis aeruginosa. The strain HY displayed high algicidal activity toward Microcystis aeruginosa cells, with a removal rate of 93.04% within 2 days via indirect attack. Streptomyces sp. HY also showed the ability to lyse several genera of cyanobacterial strains, including Dolichospermum, Pseudanabaena, Anabaena, and Synechocystis, whereas it showed a minor impact on the green alga Scenedesmus obliquus, demonstrating its selectivity specially for targeting cyanobacteria. Its algicidal mechanism involved damages to the photosynthesis system, morphological injury of algal cells, oxidative stress, and dysfunction of the DNA repair system. Furthermore, HY treatment reduced the expression levels of genes (mcyB and mcyD) related to microcystin biosynthesis and decreased the total content of microcystin-leucine-arginine by 79.18%. Collectively, these findings suggested that the algicidal bacteria HY is a promising candidate for harmful cyanobacterial bloom control.

Adverse role of colonial morphology and favorable function of microcystins for Microcystis to compete with Scenedesmus

In eutrophic freshwaters, Microcystis usually becomes dominant in phytoplankton communities due to the synergistic effects of its special eco-physiological traits and environmental factors. Colonial morphology can protect Microcystis from zooplankton grazing, which indirectly favors Microcystis to outcompete other phytoplankton, although the colonial form is not conducive to the absorption of nutrients. Moreover, unicellular Microcystis usually has competitive advantages over other phytoplankton due to its efficient absorption capacity for nutrients and releasing microcystins. However, the consequence of direct competition between toxic colonial Microcystis and green algae without external grazing pressure still remained unknown. In this study, the competition between toxic colonial Microcystis aeruginosa and a common green alga Scenedesmus obliquus was explored. Results showed that: (1) colonial M. aeruginosa had a higher requirement for key macro-nutrient phosphorus than S. obliquus, and thus its population declined and was replaced by S. obliquus eventually; (2) microcystins released by colonial M. aeruginosa inhibited the photosynthetic activity and growth of S. obliquus at early stage of the competition; (3) the photosynthetic potential of colonial M. aeruginosa was stimulated in response to the competitive stress from S. obliquus, although the population of colonial M. aeruginosa declined eventually; (4) microcystin production of colonial M. aeruginosa was enhanced by phosphorus limitation due to S. obliquus competition and was positively related to photosynthetic potential of colonial M. aeruginosa. These results indicated that, in the absence of complex natural environment, colonial Microcystis cannot outcompete Scenedesmus in a pure competition, although microcystins can play a favorable role in the competition, which clarified the opposite role of colonies and microcystins in the competition of colonial Microcystis against other phytoplankton.

Statistical optimization for simultaneous removal of methyl red and production of fatty acid methyl\xa0esters using fresh alga Scenedesmus obliquus

Microalgae are a diverse group of microorganisms, the majority of which are photosynthetic in nature. Microalgae have different applications, the most important of which is the biological treatment of wastewater. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. Microalgae grow in various types of wastewater, such as wastewater polluted by Azo dyes, due to microalgae using wastewater as a culture medium, which contains many nutrients like nitrogen, phosphate, and carbon sources. So, microalgae are used for bioremediation of wastewater due to the efficiency of growing in wastewater and for the high production of lipids followed by trans-esterification to biodiesel. Face-centered central composite design (FCCCD) was used to determine the factors that have the most significant impact on the simultaneous decolorization of methyl red and lipid production by the fresh green alga Scenedesmus obliquus. The predicted results indicated that the alga decolorized 70.15% methyl red and produced 20.91% lipids by using 1 g/L nitrogen, an incubation time of 10 days, a pH of 8, and the concentration of methyl red is 17.65 mg/L. The dry biomasses of S. obliquus were also examined by SEM and FTIR before and after treatment with methyl red. SEM and FTIR showed that the properties of dry S. obliquus were altered after the biosorption of methyl red. According to GC–MS analysis of hexane extracts of S. obliquus, the lipid profile differed before and after methyl red decolorization. The results proved that it is possible to use S. obliquus to remove dyes and produce renewable fuels such as biodiesel. The novelty of this study is that this is the first time in which the effect of nitrogen concentrations in the medium used for algal growth on the removal of dye has been studied.

Multiple roles of bamboo as a regulator of cyanobacterial bloom in aquatic systems

To understand the potential roles of terrestrial bamboo on controlling cyanobacterial blooms in aquatic systems, growth rates of the cyanobacterium Microcystis aeruginosa and its competitor algae were examined under different concentrations of bamboo extract. In mono-species cultures with unicellular algal strains, 5.0 g L−1 extract treatment suppressed M. aeruginosa growth, while it had little effect on the growth of green alga Scenedesmus obliquus or promoted the growth of diatom Nitzschia palea. In co-species cultures, the extract treatment increased the effect of S. obliquus and N. palea on the growth of M. aeruginosa. Under the extract treatment with a field-collected M. aeruginosa population, its cell density declined and its colony was etiolated and sank, while co-cultured N. palea increased explosively by invading the colony. These results suggest that bamboo forest stands along banks and artificially installed bamboo poles can affect the aquatic environment for phytoplankton community. Enhancing the growth of competitors, especially diatoms that can invade cyanobacterial colonies, by using extracts or by providing substrates for growth, was suggested to be the major way of the bloom control by bamboo.

Effects of hydrogen peroxide on Scenedesmus obliquus: Cell growth, antioxidant enzyme activity and intracellular protein fingerprinting

Hydrogen peroxide (H2O2) is an environmental-friendly algicide and it is widely used to control algal blooms in aquatic ecosystems. However, the response of algal cell metabolic characteristics and intracellular protein profile under H2O2 stress is still not well understood. In the present study, the green alga Scenedesmus obliquus was exposed to different concentrations of H2O2 (0, 2, 6, 8 and 10 mg L−1) to evaluate the changes in algal morphological, physiological, and proteomic features to H2O2 exposure. The results showed that 8 mg L−1 of H2O2 could effectively inhibit the cell growth and photosynthetic activity of S. obliquus including chlorophyll-a content and chlorophyll fluorescence parameters. The increased activities of superoxide dismutase (SOD) and catalase (CAT) observed in this study indicate that cells exposure to H2O2 caused oxidative stress. The metabolic activity of S. obliquus was significantly decreased by H2O2 treatment. In terms of proteomic analysis, 251 differentially expressed proteins (DEPs) were successfully identified. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis revealed significant protein enrichment in the metabolic pathways, photosynthesis, ascorbic acid, and alginate metabolism and phenylpropane biosynthesis of S. obliquus. The analysis of protein-protein interaction system shows that the pathways of photosynthesis and metabolic pathways of S. obliquus were essential to resist oxidative stress. Taking together, these results shed new lights on exploring the cell physiological metabolism and intracellular protein mechanisms of H2O2 inhibition on algal blooms.

Combined toxicity of nano-TiO2 and Cd2+ to Scenedesmus obliquus: Effects at different concentration ratios

The continuous release of manufactured nanomaterials (MNMs) to environments raised concerns on their combined toxicological risks with co-existing contaminants, since MNMs might severely alter the environmental behavior and fate of the contaminants. In this study, the combined toxicity of nano-sized titanium dioxide (nTiO2) and cadmium (Cd2+) to the green alga Scenedesmus obliquus and the underlying physicochemical mechanisms were investigated for the first time at different concentration ratios of Cd2+ to nTiO2 to closely mimic the realistic environment scenarios where the concentration ratios of nTiO2 to other contaminants are constantly changing. Our results suggested that under the co-exposure to different concentration ratios of Cd2+ to nTiO2, the co-exposure contaminants exhibited three different combined toxicity modes (antagonistic, partially additive, and synergistic). Specifically, antagonistic combined toxicity was observed under co-exposure to a low concentration ratio of nTiO2 to Cd2+ as the absorption by nTiO2 decreased the bioavailability of Cd2+. However, the partially additive and synergistic combined toxicity occurred when the proportion of nTiO2 in the co-exposure system was relatively high, which would mechanically and/or oxidatively damage the alga cell structures. Even worse, as a carrier of Cd2+, nTiO2 enhanced the amount of Cd2+ entering cells, which significantly enhanced the toxicity of Cd2+ to algae. Overall, we demonstrated that concentration ratios of nTiO2 to Cd2+ play an important role in determining the combined toxicity mode, which would provide a novel reference to environmental and health risk assessment of co-exposure to conventional pollutants and MNMs.

Impacts of ZnO nanoparticles on growth and antioxidant enzymes of the green alga Scenedesmus obliquus

The growing passion for new industrial technology, using innovative materials such as nanoparticles (NPs) which reached water bodies as wastewater, heavily influenced aquatic organisms and consequently the human life. Physiological characteristics of the micro-green alga Scenedesmus obliquus can be used as biomarker to evaluate the effects of the newly invited zinc oxide nanoparticles (ZnO NPs). S. obliquus was exposed to different concentrations of ZnO NPs. The recorded results clarify not only an obvious inhibition in growth but also disturbance in the production of the tested antioxidant enzymes, where both Glutathione reductase (GR) and Glutathione peroxidase gradually increase with ZnO NPs concentration giving its maximum within 100 μg Zn NP.L–1 at the end of the experiment (562 and 0.42 μg.μg–1 respectively). However, in the case of Glutathione (GSH), Glutathione S-transferase (GST) and catalase (CAT) the gradual increase recorded only during the first 24 h, while Superoxide Dismutases (SOD) started to decrease within concentration of 50 μg L–1ZnO NPs. Scanning electron microscope clarifies abnormalities in the cytomorphological characteristics of the treated cells where the cells tended to aggregate in a cluster and take elongated and spindle-shaped and/or wrapping. The various responses to ZnO NPs concentrations reflected, the disposal of ZnO nanoparticles in the environment affecting growth, morphological, and physiological characteristic of the cell.

Species-specific effects of macrophytes on the anti-grazer morphological defense in Scenedesmus obliquus

Predation and competition are the primary interspecies interactions in aquatic ecosystem. Understanding how these two stressors interactively affect the organisms is critical to predict the food web dynamics. Here, we investigated the responses of the green alga Scenedesmus obliquus to predation risk from zooplankton (Daphnia magna) and to allelopathy from four macrophytes (Cabomba furcate, Nymphoides hydrophylla, Lemna minor and Chara sp.) separately and jointly. Neither the Daphnia-derived cues nor the four macrophyte exudates affected the algal growth rate compared with those in control. Nonetheless, both the two stressors induced the multicelled colony formation in S. obliquus, which was, however, much more strongly induced by the Daphnia cues. In addition, the four macrophytes differentially altered the anti-grazer morphological defense in algae: exudates from Nymphoides and Chara markedly promoted the enhancing effect of Daphnia cues on the eight-celled colonies formation, resulting in the increased number of cells per particle of the algal population. Nonetheless, more four-celled colonies but fewer eight-celled colonies were formed under Lemna exudates exposure, in contrast to the unchanged multicelled colonies growing in Cabomba exudates under Daphnia cues exposure. The results revealed that macrophytes allelopathically disturbed the anti-grazer morphological defense in phytoplankton even though they had no direct impact on algal growth, and this interference was species-specific in macrophyte. As a result, the predator-prey interactions between herbivores and phytoplankton can be potentially changed differently in different macrophyte-dominated freshwaters, contributing to the new cognition of the important role of macrophytes in ecosystem functioning. It suggests that the algal morphology can function as a useful indicator of phytoplankton response to simultaneous stresses from predation and competition.

Effects and possible mechanisms of sanguinarine on the competition between Raphidiopsis raciborskii (Cyanophyta) and Scenedesmus obliquus (Chlorophyta): A comparative toxicological study

The phytogenic algicide sanguinarine shows strong inhibitory effects on some bloom-forming cyanobacteria and exhibits great potential in cyanobacterial bloom mitigation. To evaluate the possible ecological effects of sanguinarine on microalgae, the effects and possible mechanisms of sanguinarine on the competition between bloom-forming cyanobacterium Raphidiopsis raciborskii (formerly named Cylindrospermopsis raciborskii) and green alga Scenedesmus obliquus were investigated through co-culture competition test and comparative toxicological study including growth characteristics, chlorophyll fluorescence transients, activities of antioxidant enzymes, and lipid peroxidation. The results of Raphidiopsis-Scenedesmus co-culture competition test showed that sanguinarine decreased the competition ability of R. raciborskii, which benefitted S. obliquus in winning the competition. Toxicological studies have shown that sanguinarine exhibited high inhibitory effects on the growth and photosynthesis of R. raciborskii but no obvious toxicity on S. obliquus at concentrations of no more than 80 μg L−1. Oxidative damage partially contributed but was not the primary mechanism for the toxicity of sanguinarine on R. raciborskii. The results presented in this study indicate that sanguinarine may be a good algicidal candidate in mitigation of Raphidiopsis-based water bloom.

Dynamic changes in community composition of Scenedesmus-seeded artificial, engineered microalgal biofilms

Artificial, non-sterile, microalgal biofilms present a promising biotechnological avenue for the production of valuable biomass, biofuels and biochemicals while simultaneously engaging in photosynthetic carbon capture. Here we use a psbA amplicon library and high-throughput 16S and 18S rRNA gene sequencing to investigate the effects of time and CO2 concentration on the composition and community dynamics of photoautotrophically grown microalgal biofilms pre-conditioned with wastewater and heavily seeded with the green alga Scenedesmus obliquus. While biomass increased in a stable, linear manner, our analysis revealed that the photoautotrophic community dramatically changed over time. Photoautotrophs such as Chorella and the cyanobacterium Leptolyngbya, presumably seeded from the wastewater, rapidly established as constituents of the biofilm while the seed species was far less dominant than anticipated. With time, photoautotrophic diatoms and dinoflagellates also established themselves as constituents of the biofilm. Low CO2 (0.04% v/v) favoured the early proliferation of cyanobacteria while high CO2 (12%) delayed, but did not prevent the proliferation. In addition, a phylogenetically diverse array of heterotrophic α-, β- and γ-proteobacteria, Bacteriodetes along with a selection of eukaryotic microorganisms inhabited the biofilms. Principal coordinate analyses reveal unique clustering patterns indicating that the composition of the initial and the final microbial communities were distinctly different from one another. Alpha diversity measures indicated that the 16S (prokaryotic) community peaked around day 10 / 11 at both 0.04% and 12% CO2. However, unlike the 18S (eukaryotic) community where diversity was at a maximum at the end of the 26-day time-course, prokaryotic diversity achieved minimum values, particularly for biofilms grown at 0.04% CO2, where the cyanobacteria proliferated. In spite of the planned experimental design bias toward S. obliquus biofilm growth, the collective data suggest that selection against undesirable microorganism also needs to be incorporated as an essential feature of biofilm photobioreactor design and operation.

Photosynthetic toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) on green algae Scenedesmus obliquus

The widespread use of pharmaceuticals and personal care products (PPCPs) has raised serious concerns regarding their potential ecotoxicological effects. We examined the photosynthetic toxicity of four non-steroidal anti-inflammatory drugs (NSAIDs), i.e. ibuprofen (rac-IBU and S-(+)-IBU), aspirin (ASA) and ketoprofen (KEP) on the green alga Scenedesmus obliquus. Our results showed that NSAIDs exerted inhibitory effects on algal growth; the IC50-24h of S-(+)-IBU, rac-IBU, ASA, and KEP was 123.29, 107.91, 103.05, and 4.03 mg/L, respectively. KEP was the most toxic, ASA was slightly more toxic than rac-IBU, and S-(+)-IBU was the least toxic. NSAIDs adversely affected the cellular ultrastructure, as evident from plasmolysis, chloroplast deformation and disintegration. NSAID treatments decreased the chlorophyll and carotenoid content, and chlorophyll fluorescence parameters such as minimum fluorescence yield (F0), maximum fluorescence yield (Fm), maximum photochemical quantum yield (Fv/Fm), PSII (photosystem II) effective quantum yield [Y(II)], photosynthetic electron transfer rate (ETR), and the photochemical quenching (qP), were also adversely affected. Algal photosynthetic and respiratory rates decreased following NSAID treatments, and the expression of genes involved in photosynthetic electron transport (psaA, psaB, psbB, psbD, and rbcL) was down-regulated. Furthermore, the functioning of the photosynthetic electron transport chain from PSI (photosystem I) to PSII, carbon assimilation, and photorespiration were affected. Our results suggest that NSAIDs can exert considerable toxic effects on the photosynthetic system of S. obliquus. These results provide a basis for evaluating the environmental safety of NSAIDs.

Salt response of the freshwater microalga Scenedesmus obliquus (Turp.) Kutz is modulated by the algal growth phase

Growth and biochemical responses of the coenobial green alga Scenedesmus obliquus to salinity stress were monitored across different phases of growth. The alga was cultured on BG11 growth medium and subjected to 0, 30, 100, and 200 mmol/L NaCl for a period of 20 d, during which algal cultures were harvested at 4-d intervals. The salinity-induced inhibition of algal growth was accompanied with prolongation of timing of the different growth phases. The sharp and progressive salinity-induced inhibition of algal growth rate during the early phase of growth points to salt shock but moderation of inhibition at the subsequent stages of growth means algal acclimation to salinity. The concentrations of chlorophylls a and b, soluble sugars, proteins as well as those of K+ and Na+ in the alga exhibited peaks at the initiation of the exponential phase of growth, with increasing magnitude in proportion to the increase in the level of salinity. Nevertheless, whereas soluble sugars of the alga peaked at initiation of the exponential phase, starch concentration progressively increased with culture age, reaching saturation towards the stationary phase. Whereas the salinity-induced increase in soluble sugars was most evident at the early stages of growth the reverse was true for starch. The present results point to fast acclimation of S. obliquus to salt stress post a brief salt shock, utilizing soluble sugars, K+ and Na+ for osmotic adjustment. Increasing salinity from 0 to 200 mmol/L NaCl led to progressive increase in soluble sugars, proteins, K + and Na + concentrations of the algal cells, particularly at the early stages of growth. However, the salinity-induced increase in chlorophyll concentration approached a limit at 100 mmol/L NaCl whereas that in starch concentration was more evident at the later stages of growth.

Comparative biodegradation of all chlorinated phenols by the microalga Scenedesmus obliquus — The biodegradation strategy of microalgae

This work presents the comparative biodegradation of all chlorinated phenolic compounds by the green alga Scenedesmus obliquus and determines the microalgal bioenergetic strategy. The microalga manages its energy reserves rationally by investing them, either on growth or on the biodegradation of the toxic compound. The microalga seems to follow two distinct detoxification strategies. In the first one, when microalgae are surrounded by relatively low toxic phenolic compounds (phenol, monochlorophenols, 2,4-dichlorophenol and 2,6-dichlorophenol), they use all, or at least more of their energy reserves to increase the biomass production and not the biodegradation. In the second one, when surrounded by higher toxic chlorophenols (meta-substituted dichlorophenols, trichlorophenols, tetrachlorophenols and pentachlorophenol) the microalgae invest more, or all of their energy reserves directly in the biodegradation of the toxic compounds, while less or no energy is invested in biomass increase. The microalga biodegraded in five days approximately 9% of the lower toxic phenol and 90% of the higher toxic pentachlorophenol. Considering our ability to interfere with microalgae energy reserves, which define their stress tolerance in the toxic environment, and knowing the microalgal bioenergetic strategy, we could easily use microalgae to biodegrade toxic wastes in the frame of a rational biotechnological approach in the near future.

Influence of humic substances on the toxic effects of cadmium and SDBS to the green alga Scenedesmus obliquus

The joint toxicity of chemicals mixture in the aquatic environment was still not well clear. To clarify the joint toxicity of the mixtures of metals and organic pollutants, as well as the influence of dissolved organic matter (DOM) in field water-body on their toxic effects, we conducted the toxicity tests with cadmium (Cd) and sodium dodecyl benzene sulfonate (SDBS) on Scenedesmus obliquus (S. obliquus) with or without the presence of fulvic acid (FA), a typical of DOM. Our results showed Cd was more toxic to S. obliquus than SDBS, and the effects of fulvic acid on SDBS were greater than Cd. The joint toxicity of Cd and SDBS expressed a synergistic effect on S. obliquus, which was observed to be increased with the presence of FA. Our results gave an example for the joint toxicity investigations of organics and metals, aiding to understanding the toxicity of pollutant mixtures in field water bodies containing DOM.

Dissolved organic matter and aluminum oxide nanoparticles synergistically cause cellular responses in freshwater microalgae

ABSTRACTThis study investigated the impact of dissolved organic matters (DOM) on the ecological toxicity of aluminum oxide nanoparticles (Al2O3NPs) at a relatively low exposure concentration (1 mg L−1). The unicellular green alga Scenedesmus obliquus was exposed to Al2O3NP suspensions in the presence of DOM (fulvic acid) at various concentrations (1, 10, and 40 mg L−1). The results show that the presence of DOM elevated the growth inhibition toxicity of Al2O3NPs towards S. obliquus in a dose-dependent manner. Moreover, the combination of DOM at 40 mg L−1 and Al2O3NPs resulted in a synergistic effect. The relative contribution of Al-ions released from Al2O3NPs to toxicity was lower than 5%, indicating that the presence of the particles instead of the dissolved ions in the suspensions was the major toxicity sources, regardless of the presence of DOM. Furthermore, DOM at 10 and 40 mg L−1 and Al2O3NPs synergistically induced the upregulation of intercellular reactive oxygen species levels and superoxide dismutase activities. Analysis of the plasma malondialdehyde concentrations and the observation of superficial structures of S. obliquus indicated that the mixtures of DOM and Al2O3NPs showed no significant effect on membrane lipid peroxidation damage. In addition, the presence of both DOM and Al2O3NPs contributed to an enhancement in both the mitochondrial membrane potential and the cell membrane permeability (CMP) in S. obliquus. In particular, Al2O3NPs in the presence of 10 and 40 mg L−1 DOM caused a greater increase in CMP compared to Al2O3NPs and DOM alone treatments. In conclusion, these findings suggest that DOM at high concentrations and Al2O3NPs synergistically interrupted cell membrane functions and triggered subsequent growth inhibition toxicity.

Removal of pharmaceutical pollutants from synthetic wastewater using chemically modified biomass of green alga Scenedesmus obliquus

Pharmaceutical compounds are considered emerging environmental pollutants that have a potential harmful impact on environment and human health. In this study, the biomass of alga (Scenedesmus obliquus) was modified using alkaline solution, and used for the biosorption of tramadol (TRAM) and other pharmaceuticals. The adsorption kinetics and isotherms were investigated. The obtained results reveal high adsorption capacity of tramadol over modified algal biomass (MAB) after 45min with removal percentage of 91%. Pseudo-second order model was well fitted with the experimental data with correlation coefficient (0.999). Biosorption of tramadol on modified algal biomass proceeds with Freundlich isotherm model with correlation coefficient (0.942) that emphasized uptake of TRAM by MAB is driven by chemisorption. FTIR spectra of MAB before and after the adsorption were analyzed; some IR bands were detected with slight shift and low intensity suggesting their involving in adsorption. The tramadol biosorption by MAB is a chemical process as confirmed by Dubinin-Radushkevich. The adsorption of pharmaceutical over MAB is mainly preceded by hydrophilic interactions between amino and carbonyl groups in pharmaceutical molecules and hydroxyl and carbonyl functional groups on surface of biosorbent. It was emphasized by disappearance O-H and C-O from biomass IR spectra after adsorption. In matrix of pharmaceutical, the recorded adsorption capacities for CEFA, PARA, IBU, TRAM and CIP are 68, 58, 42, 42 and 39mg/g over MAB at natural pH and MAB dose of 0.5g/L. Furthermore, oxygen uptake by bacteria was applied for estimate the toxicity of pharmaceutical. The recorded result concluded the efficient reusability of modified algal biomass for biosorption of pharmaceuticals, as well only the adsorption efficiency decreased by 4.5% after three runs. Subsequently, the modified algal biomass is a promising reusable adsorbent for decontamination of wastewater from pharmaceuticals.

Bioenergetic reprogramming plasticity under nitrogen depletion by the unicellular green alga Scenedesmus obliquus.

Simultaneous nitrogen depletion and 3,4-dichlorophenol addition induce a bioenergetic microalgal reprogramming, through strong Cyt b 6 f synthesis, that quench excess electrons from dichlorophenol's biodegradation to an overactivated photosynthetic electron flow and H 2 -productivity. Cellular energy management includes "rational" planning and operation of energy production and energy consumption units. Microalgae seem to have the ability to calculate their energy reserves and select the most profitable bioenergetic pathways. Under oxygenic mixotrophic conditions, microalgae invest the exogenously supplied carbon source (glucose) to biomass increase. If 3,4-dichlorophenol is added in the culture medium, then glucose is invested more to biodegradation rather than to growth. The biodegradation yield is enhanced in nitrogen-depleted conditions, because of an increase in the starch accumulation and a delay in the establishment of oxygen-depleted conditions in a closed system. In nitrogen-depleted conditions, starch cannot be invested in PSII-dependent and PSII-independent pathways for H2-production, mainly because of a strong decrease of the cytochrome b 6 f complex of the photosynthetic electron flow. For this reason, it seems more profitable for the microalga under these conditions to direct the metabolism to the synthesis of lipids as cellular energy reserves. Nitrogen-depleted conditions with exogenously supplied 3,4-dichlorophenol induce reprogramming of the microalgal bioenergetic strategy. Cytochrome b 6 f is strongly synthesized (mainly through catabolism of polyamines) to manage the electron bypass from the dichlorophenol biodegradation procedure to the photosynthetic electron flow (at the level of PQ pool) and consequently through cytochrome b 6 f and PSI to hydrogenase and H2-production. All the above showed that the selection of the appropriate cultivation conditions is the key for the manipulation of microalgal bioenergetic strategy that leads to different metabolic products and paves the way for a future microalgal "smart" biotechnology.

Effects of temperature, genetic variation and species competition on the sensitivity of algae populations to the antibiotic enrofloxacin

Primary producers are amongst the most sensitive organisms to antibiotic pollution in aquatic ecosystems. To date, there is little information on how different environmental conditions may affect their sensitivity to antibiotics. In this study we assessed how temperature, genetic variation and species competition may affect the sensitivity of the cyanobacterium Microcystis aeruginosa and the green-algae Scenedesmus obliquus to the antibiotic enrofloxacin. First, we performed single-species tests to assess the toxicity of enrofloxacin under different temperature conditions (20°C and 30°C) and to assess the sensitivity of different species strains using a standard temperature (20°C). Next, we investigated how enrofloxacin contamination may affect the competition between M. aeruginosa and S. obliquus. A competition experiment was performed following a full factorial design with different competition treatments, defined as density ratios (i.e. initial bio-volume of 25/75%, 10/90% and 1/99% of S. obliquus/M. aeruginosa, respectively), one 100% S. obliquus treatment and one 100% M. aeruginosa treatment, and four different enrofloxacin concentrations (i.e. control, 0.01, 0.05 and 0.10mg/L). Growth inhibition based on cell number, bio-volume, chlorophyll-a concentration as well as photosynthetic activity were used as evaluation endpoints in the single-species tests, while growth inhibition based on measured chlorophyll-a was primarily used in the competition experiment. M. aeruginosa photosynthetic activity was found to be the most sensitive endpoint to enrofloxacin (EC50–72h =0.02mg/L), followed by growth inhibition based on cell number. S. obliquus was found to be slightly more sensitive at 20°C than at 30°C (EC50–72h cell number growth inhibition of 38 and 41mg/L, respectively), whereas an opposite trend was observed for M. aeruginosa (0.047 and 0.037mg/L, respectively). Differences in EC50–72h values between algal strains of the same species were within a factor of two. The competition experiment showed that M. aeruginosa growth can be significantly reduced in the presence of S. obliquus at a density ratio of 75/25% M. aeruginosa/S. obliquus, showing a higher susceptibility to enrofloxacin than in the single-species test. The results of this study confirm the high sensitivity of cyanobacteria to antibiotics and show that temperature and inter-strain genetic variation may have a limited influence on their response to them. The results of the competition experiment suggest that the structure of primary producer communities can be affected, at least temporarily, at antibiotic concentrations close to those that have been measured in the environment.