Unicellular Green Alga Chlorella Research Articles

Anti-diabetic Activity of Spirulina and Chlorella in In vivo Experimental Rats

The effects of supplying experimental rats with unicellular green algae Chlorella and tiny filamentous cyanobacteria Spirulina, on type 2 diabetes (T2DM) were examined in the present study. Eight sets of male Sprague-Dawley albino rats, each with six individuals, were used in the investigation. Throughout the trial, Group 1 was the negative control group and was given saline regularly. Group 2 was given alloxan to induce diabetes. Spirulina was given to groups 3, 4, and 5 at dosages of 100, 200, and 300 mg/kg body weight, respectively, after diabetes induction. Similarly, groups 6, 7, and 8 received dosages of 100, 200, and 300 mg/kg body weight of Chlorella, respectively. The findings indicated that the control group had significantly higher levels of triglycerides, low-density lipoprotein (LDL), blood sugar, and very low-density lipoprotein (VLDL) and considerably lower levels of insulin, high-density lipoprotein (HDL), and phospholipids. However, rats given Spirulina (groups 3, 4, and 5) showed notably higher insulin, HDL, and phospholipids levels and significantly lower blood glucose, cholesterol, VLDL, LDL, and triglycerides levels. Rats fed with Chlorella (groups 6, 7, and 8) also showed increased effectiveness of feed ratios, greater final weights, and body weight growth percentages compared to the control group. The present study shows that supplementing with Spirulina and Chlorella improves insulin lipid patterns, blood sugar, and type 2 diabetes in vivo laboratory rats. According to the research, Spirulina and Chlorella may be used as functional meals to help control and cure diabetes.

Acclimation mechanism of microalgal photosynthetic apparatus under low atmospheric pressures - new astrobiological perspectives in a Mars-like atmosphere.

This study reveals a new acclimation mechanism of the eukaryotic unicellular green alga Chlorella vulgaris in terms of the effect of varying atmospheric pressures on the structure and function of its photosynthetic apparatus using fluorescence induction measurements (JIP-test). The results indicate that low (400mbar) and extreme low (2 atmosphere (simulating the Mars atmosphere), reveals that the impact of extremely low atmospheric pressure on PQ mobility within the photosynthetic membrane, coupled with the low density of an almost 100% CO2 Mars-like atmosphere, results to a similar photosynthetic efficiency to that on Earth. These findings pave the way for the identification of novel functional acclimation mechanisms of microalgae to extreme environments that are vastly distinct from those found on Earth.

Enhanced reducing sugar production and extraction for Chlorella vulgaris in mixotrophic cultivation using high hydrostatic pressure processing and ultrasound

ABSTRACT Although extraction of polysaccharides to convert reducing sugars (RS) from microalgae by acid or alkali pretreatments and enzymatic hydrolysis has been extensively studied, few reports exploring the use of high hydrostatic pressure processing (HHP) and ultrasonication (US) as emerging technologies for the extraction of sugars from microalgae biomass exist. Thus, the present study was conducted to determine the effects of mixotrophic growth and stress conditions (NaNO3 and CO2 concentration and light intensity) on RS and protein accumulation in the unicellular green alga Chlorella vulgaris in addition to optimization of the effectiveness of the sequential applications of HHP and US with dilute acid as well as simultaneous enzymatic saccharification on the production of RS from microalga cells. High light intensity, high CO2 concentration and limited nitrogen concentration promoted RS production. The maximum protein content (0.0683 mg g‒1) was achieved at 0.3 g l‒1 NaNO3 concentration, 7000 μmol photons m‒2 s‒1 and 6 l min‒1 CO2 concentration. The highest RS content of C. vulgaris after 48 h enzymatic saccharification (583.86 ± 13.23 mg g‒1) was obtained at 1% (w/w) acid concentration and 80% amplitude for 30 min with 79.4% RS yield. Combined US-assisted dilute acid pretreatment and enzymatic hydrolysis were also found to be more effective than HHP assisted dilute acid pretreatment and enzymatic saccharification. Therefore, microalgal biomass can be considered a suitable renewable feedstock used in fermentation.

Heterotrophically Ultrahigh-Cell-Density Cultivation of a High Protein-Yielding Unicellular Alga Chlorella With a Novel Nitrogen-Supply Strategy.

The unicellular green alga Chlorella is an ideal protein source. However, the high production cost and low production capability of the current main photoautotrophic culture mode limit its application especially as an alternative protein source for food and feed, which might be overcome through high-cell-density cultivation in fermenters. In this study, a Chlorella sorokiniana strain CMBB276 with high protein content was selected from five Chlorella strains by comprehensive evaluation of their growth rates, protein contents, and yields. The optimal cultural temperature, pH, and mole ratio of carbon and nitrogen (C/N) for C. sorokiniana CMBB276 growth were found to be 30°C, 6.5, and 18, respectively. Ammonium chloride was proved to be the best nitrogen (N) source for C. sorokiniana CMBB276 growth, whereas growth inhibition caused by the accumulation of salts was observed under fed-batch cultivation when maintaining a constant C/N ratio of 18 by controlling pH with sodium hydroxide solution. By simultaneously reducing the concentration of ammonium chloride in the feeding medium and controlling pH with ammonium hydroxide, we finally achieved the ultrahigh-cell-density cultivation of C. sorokiniana CMBB276. The highest biomass concentration and protein yield reached 232 and 86.55 g l−1, respectively, showing the great potential of culturing C. sorokiniana CMBB276 in fermenters for economic and large-scale protein source production.

The Microalga Chlorella vulgaris as a Natural Bioenergetic System for Effective CO2 Mitigation—New Perspectives against Global Warming

In the present contribution, the differentiation in the molecular structure and function of the photosynthetic apparatus of the unicellular green alga Chlorella vulgaris was studied at several light intensities (0–400 μmol m−2 s−1) and various CO2 concentrations (0.04–60% CO2), in completely autotrophic conditions. Asymmetries that occur by different light intensities and CO2 concentrations induce metabolic and functional changes. Using chlorophyll fluorescence induction techniques (OJIP test), we showed that Chlorella vulgaris tolerates extremely high CO2 levels and converts them photosynthetically into valuable products, including O2 and biomass rich in carbohydrates and lipids. Interestingly, the microalga Chlorella vulgaris under extremely high CO2 concentrations induces a new metabolic state intensifying its photosynthetic activity. This leads to a new functional symmetry. The results highlight a potent CO2 bio-fixation mechanism of Chlorella vulgaris that captures up to 288 L CO2 L PCV−1 day−1 under optimal conditions, therefore, this microalga can be used for direct biological CO2-reducing strategies and other green biotechnological applications. All of the above suggest that Chlorella vulgaris is one of the most prominent competitors for a closed algae-powered bioreactor that is able to consume huge amounts of CO2. Thus, it is a sustainable and natural bioenergetic system with perspectives in dealing with major environmental issues such as global warming. In addition, Chlorella vulgaris cultures could also be used as bioregeneration systems in extraterrestrial missions for continuous atmospheric recycling of the human settlements, paving the way for astrobiological applications.

Using DMSO for chlorophyll spectroscopy

DMSO (dimethyl sulphoxide, (CH3)2SO) is an alternative solvent for spectroscopic assay of chlorophylls (Chls) but has mainly been used on Chl a & b organisms. Here, we develop algorithms for the estimation of Chl a, b & c1c2, and d in DMSO solvent. The common unicellular green alga Chlorella sp. (Chl a & b) is used as an example of an oxygenic photo-organism with Chl a as the primary photosynthetic pigment and Chl b as the accessory Chl. The cyanobacterium Synechococcus is used as an example of organisms containing only Chl a. The diatom Chaetoceros sp. is used as the representative Chl a & c1c2 organism. The unusual chlorobacterium Acaryochloris marina has Chl d & a. Algorithms for use on mixed phytoplankton and algal mats (Chl a, b & c) were also developed. The algorithms for DMSO solvent are compared to those developed for 90% acetone as the benchmark solvent. DMSO solvent offers the advantages of low volatility, low toxicity, low flammability, biodegradability, and ease of transport and is an effective extractant of chlorophylls. However, there appear to be significant storage problems with DMSO extracts of chlorophylls because of its high freezing point (+18.4°C) and probable breakdown in chlorophylls in DMSO over several days.

The chloroplast genetic engineering of a unicellular green alga Chlorella vulgaris with two foreign peptides co-expression

The purpose of this study was to establish a chloroplast transformation system in Chlorella vulgaris for expressing recombinant proteins. The 16S-trnI/trnA-23S in the inverted repeat region of C. vulgaris chloroplast genome was used as the flanking fragments in the homologous recombination vector. Meanwhile, the selectable marker aadA gene was promoted by the endogenous 16S promoter, and two codon-optimized antimicrobial peptide NZ2114 and Piscidin-4 genes linked by endogenous ribosome binding site (RBS) in a polycistron were regulated by the rbcL promoter of C. vulgaris. The plasmid was transformed into the chloroplast of C. vulgaris via microparticle bombardment and the transformants were screened using spectinomycin. After multiple rounds' selection, the homoplastic transformants were identified using polymerase chain reaction (PCR), Southern blotting, and Western blotting. This research provided an efficient chloroplast genetic system for C. vulgaris, and will be benefit for the algal further research and application.

Metabolomics reveals the inhibition on phosphorus assimilation in Chlorella vulgaris F1068 exposed to AgNPs

Phosphorus removal by algae-based biotechnology can be achieved through algal assimilation, surface adsorption, or abiotic precipitation. However, there are still unavailable how these phosphorus removal processes were affected by nanoparticles in wastewater. Here, we employed a non-targeted metabolomic approach to reveal the impact of silver nanoparticles (AgNPs) on the phosphorus assimilation by a unicellular green alga Chlorella vulgaris F1068 (C. vulgaris F1068). Results showed that AgNPs mostly inhibited total phosphorus (TP) removal by the algal assimilation, with TP removal efficiency being reduced by 66.2% (with 0.20 mg/L AgNPs) of the control (without AgNPs). Metabolomics analysis also indicated that AgNPs disturbed metabolic responses related to phosphorus assimilation. AgNPs inhibited phospholipid metabolism which included inositol phosphate metabolism and phosphatidylinositol signaling system (downregulation of glycerol-3-phosphate and myo-inositol, as well as upregulation of serine). Metabolites related to phosphorus assimilation products were impacted through downregulation of guanine, glutamine, alanine, and aspartic acid, as well as upregulation of succinic acid, thereby impeding the algal assimilation of phosphorus. Moreover, perturbation of glutathione metabolism induced by oxidative stress stimulated the alteration of membrane state (upregulation of glycine). These findings contribute to a molecular-scale perspective of nanoparticles on algae-based biotechnology in phosphorus removal.

Metabolic plasticity of the starchless mutant of Chlorella sorokiniana and mechanisms underlying its enhanced lipid production revealed by comparative metabolomics analysis

The unicellular green alga Chlorella sorokiniana is of great industrial interest for biofuels production due to its rapid growth, high lipid content, and capabilities in tolerating broad environment and cultivation conditions. C. sorokiniana can grow under both heterotrophic and photoautotrophic conditions, which offers opportunities to produce lipids from this species/strain by employing coupled heterotrophic and phototrophic cultivation mode. In this study, a starchless mutant SLM2 was successfully obtained by high-throughput screening of the chemical mutagenesis pool of a C. sorokiniana strain that has the potential to achieve high cell density under heterotrophic conditions, aiming to enhance its lipid content and productivity. Unexpectedly, enhanced lipid production was only observed in photoautrophically-grown SLM2 cells subjected to stress conditions (i.e. high-light and nutrient limitation). When the heterotrophically-grown cells were subjected to the same stress conditions that can trigger lipid accumulation, less differences in lipid productivities were observed between wild type (WT) and SLM2. To understand metabolic basis underlying such a discrepancy, comparative time-course metabolomics analysis was performed for SLM2 and WT from different cultivation conditions. The results highlighted up-regulated metabolic flux related to the increased lipid biosynthesis in the phototrophically-grown starchless mutant cells, which included enhanced oxidative pentose phosphate pathway in a mode favoring NADPH production, and the augmented glycolysis pathway providing precursors for both fatty acids and glycerol backbone synthesis. In SLM2, the classical TCA cycle is down-regulated, while its bypass the gamma-aminobutyric acid (GABA) shunt is triggered, which is speculated to contribute to enhanced lipid accumulation in the starchless mutant as well. In addition to revealing the metabolic plasticity possessed by starchless mutant, it is suggested that photoautotrophic cultivation mode is more suitable than coupled heterotrophic and photoautotrophic cultivation mode for production of lipids by using the starchless mutant SLM2 obtained in this study.

Adsorption of Orange-G dye by the Dried Powdered Biomass of <i>Chlorella vulgaris</i> Beijerinck

Decolourization potential of microalgal biomass of an unicellular green alga ( Chlorella vulgaris ) was studied using different concentrations of Orange-G dye. Several parameters were also optimized for better removal of the tested dye from its aqueous solution. Langmuir and Freundlich models were tested for equilibrium studies and experimental data of the present study are better explained by the Freundlich model. FTIR data showed that five functional groups were probably involved in the adsorption of the dye. The biosorption process using algae (including C. vulgaris ) offers an excellent biosystem for the remediation of final discharge of textile effluents.

Disturbance of photosystem II-oxygen evolution complex induced the oxidative damage in Chlorella vulgaris under the stress of cetyltrimethylammonium chloride

Oxygen evolution complex (OEC) in photosystem II (PSII) is sensitive to environmental stressors. However, oxidative damage mechanism in PSII-OEC is still unclear. Here, we investigated photosynthetic performance of PSII, oxidative stress and antioxidant reaction induced by reactive oxygen species (ROS) in a unicellular green alga Chlorella vulgaris (C. vulgaris) under the stress of cetyltrimethylammonium chloride (CTAC). From the changes of chlorophyll fluorescence parameters and PSII activity, it was proved that the electron transport, which occurred initially at the electron donor side of OEC, was disturbed by CTAC. Moreover, a significant decrease of the oxygen evolution rate in OEC (40.95%) while an increase of ROS (50.50%) was obtained after the exposure to 0.6 mg/L CTAC compared to the control (without CTAC), confirming that more oxygen transferred to ROS under the stress. Furthermore, the increased ROS in chloroplast and the structural destruction in thylakoid membrane were observed, respectively. These results proved that oxidative damage mechanism in PSII-OEC is mainly through the reduction of oxygen evolution and the production of excessive ROS, thus leading to the destruction of OEC performance and chloroplast structure.

Circular economy fertilization: Testing micro and macro algal species as soil improvers and nutrient sources for crop production in greenhouse and field conditions

Nutrient losses from agricultural land to freshwater and marine environments contribute to eutrophication and often to the growth of algal blooms. However, the potential benefits of recycling this algal biomass back to agricultural land for soil quality and crop nutrition in a “circular-economy” has received little attention. We tested the effects of algal additions to arable soil in greenhouse-grown garden peas, and field plots of spring wheat, on plant growth and nutrition and physical and chemical properties of the soil. Representatives of five algal species, which contrasted in elemental composition, were applied at 0.2, 2 and 4 g kg−1 in the greenhouse and at 24 g m2 in the field. These included the cyanobacteria Arthrospira platensis (Spirulina), the unicellular green algae Chlorella sp., the red seaweed Palmaria palmata, and the brown seaweeds Laminaria digitata and Ascophyllum nodosum. In the greenhouse at the highest application rates (4 g kg−1), Chlorella sp., and Spirulina increased soil total nitrogen and available phosphorus, and Spirulina also increased soil nitrate concentrations. P. palmata and L. digitata significantly increased soil inorganic (NH4+ and NO3−) concentrations under all three application rates. Chlorella sp. significantly increased soil total P, N and C, available P, NH4+-N, and pea yield. Soil water-stable aggregates were unchanged by the algal additions in both the greenhouse and field study. In the field, 4 species (Chlorella sp. Spirulina, P. palmata and L. digitata) increased soil inorganic nitrogen concentrations, confirming their potential to recycle mineralizable nitrogen to agricultural soils, but no significant effects were found on wheat yields under the application rates tested.

Resource utilization of microalgae from biological soil crusts: Biodiesel production associated with desertification control

With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L-1 d-1), and achieved high lipid productivity up to 75–85 mg L-1 d-1, with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development.

Metabolic Response of the Two Marine Unicellular Algae <i>Chlorella salina</i> and <i>Dunaliella bardawil</i> to Toxicity of the Antifouling Agent Irgarol 1051

Toxic pollutants are metabolic poisons that can seriously injure or destroy the photosynthetic organisms upon which the food chain depends. Since microalgae play a key role in marine ecosystems, marine microalgae are proposed as excellent bio-indicators of pollution due to their high sensitivity, which can give warning of the toxic effects of chemicals sooner than any other species. The aim of this work concentrated on the effect of different concentrations of the antifouling biocide (Irgarol 1051) on growth and chlorophylls content (as an essential metabolite) of the two marine unicellular green algae Chlorella salina and Dunaliella bardawil that usually used in fish feeding. The growth of the wall-less Dunaliella bardawil was more sensitive to Irgarol 1051 than the walled cells Chlorella salina, although the concentrations used were greatly different. The product of photosynthesis in the two algal species greatly affected since in the presence of Irgarol 1051, a serious destructive effect was observed. The cell wall appeared to play a significant role in protecting the organism against toxicity of the antifouling agent either by adsorption or degradation. The strength of toxicity depends mainly on the concentration of the antifouling agent, the length of culturing period and the type of organism tested.

Effects of Selenite on Unicellular Green Microalga Chlorella pyrenoidosa: Bioaccumulation of Selenium, Enhancement of Photosynthetic Pigments, and Amino Acid Production.

Microalgae were studied as function bioaccumulators of selenium (Se) for food and feed supplement. To investigate the bioaccumulation of Se and its effects on the unicellular green alga Chlorella pyrenoidosa, the algal growth curve, fluorescence parameters, antioxidant enzyme activity, and fatty acid and amino acid profiles were examined. We found that Se at low concentrations (≤40 mg L-1) positively promoted algal growth and inhibited lipid peroxidation and intracellular reactive oxygen species. The antioxidative effect was associated with an increase in the levels of glutathione peroxidase, catalase, linolenic acid, and photosynthetic pigments. Meanwhile, a significant increase in amino acid and organic Se content was also detected in the microalgae. In contrast, we found opposite effects in C. pyrenoidosa exposed to >60 mg L-1 Se. The antioxidation and toxicity appeared to be correlated with the bioaccumulation of excess Se. These results provide a better understanding of the effect of Se on green microalgae, which may help in the development of new technological applications for the production of Se-enriched biomass from microalgae.

Responses triggered in chloroplast of Chlorella variabilis NC64A by long-term association with Paramecium bursaria.

The unicellular green alga Chlorella variabilis NC64A is an endosymbiont of the ciliate Paramecium bursaria. The host's control, including the transfer of biochemical substrates from P. bursaria to C. variabilis, is involved in symbiotic relationships. C. variabilis NC64A that had been re-infected to P. bursaria for more than 1year and isolated from the host showed higher chlorophyll levels compared to those in free-living cells. Unlike the host, the expression of C. variabilis NC64A heat shock 70kDa protein was independent of establishment of endosymbiosis. In symbiotic cells, the levels of PII signal transduction protein (CvPII) that coordinate the central C/N anabolic metabolism were slightly higher than those in free-living cells. Furthermore, the environmental cues (light and host food bacteria availability) affected the abundance of CvPII, suggesting that synthesis of the protein was influenced by the host. Moreover, arginine concentrations in the symbiotic algae of P. bursaria were also controlled by the host's nutritional conditions. Together, our results imply that signal substrates and/or products of metabolism in host cells might act as messengers mediating the regulation of key events in symbiont cells.

Hydrogen production by unicellular green alga chlorella sp. LSD-W2 isolated from seawater in Thailand

Green algae are able to convert the unlimited sunlight energy to produce hydrogen via photosynthesis. In seawater, several kinds of m arine microalgae are widespread and abundant and have been shown to tolerate and survive under the extreme salt concentrations . This work aimed to study the screening of high H 2 producing marine green algal strains isolated from the Gulf of Thailand and the Andaman Sea, and the selection of the highest H 2 producing strain. Its H 2 production was investigated under photoheterotrophic cultivation. The result revealed that among 20 marine green algal strains, the green alga Chlorella sp. LSD-W2 gave the highest H 2 production rate in both light and dark anaerobic conditions. During photoheterotrophic cultivation Chlorella sp. LSD-W2 was rapidly grown in TAP (Tris-Acetate-Phosphate) medium and reached the stationary growth phase after 36 h of cultivation. The highest photohydrogen production rate was found in cells incubated in NH 4 Cl-deprived TAP medium. It was approximately 20-fold higher than H 2 production rate of cells in a normal TAP medium.

Sphagnum-dominated bog systems are highly effective yet variable sources of bio-available iron to marine waters

Iron is a micronutrient of particular interest as low levels of iron limit primary production of phytoplankton and carbon fluxes in extended regions of the world's oceans. Sphagnum-peatland runoff is extraordinarily rich in dissolved humic-bound iron. Given that several of the world's largest wetlands are Sphagnum-dominated peatlands, this ecosystem type may serve as one of the major sources of iron to the ocean. Here, we studied five near-coastal creeks in North Scotland using freshwater/seawater mixing experiments of natural creek water and synthetic seawater based on a 59Fe radiotracer technique combined with isotopic characterization of dissolved organic carbon by Accelerator Mass Spectrometry. Three of the creeks meander through healthy Sphagnum-dominated peat bogs and the two others through modified peatlands which have been subject to artificial drainage for centuries. The results revealed that, at the time of sampling (August 16–24, 2014), the creeks that run through modified peatlands delivered 11–15μg iron per liter creek water to seawater, whereas the creeks that run through intact peatlands delivered 350–470μg iron per liter creek water to seawater. To find out whether this humic-bound iron is bio-available to marine algae, we performed algal growth tests using the unicellular flagellated marine prymnesiophyte Diacronema lutheri and the unicellular marine green alga Chlorella salina, respectively. In both cases, the riverine humic material provided a highly bio-available source of iron to the marine algae. These results add a new item to the list of ecosystem services of Sphagnum-peatlands.

Physicochemical transformation and algal toxicity of engineered nanoparticles in surface water samples

Most studies on the behavior and toxicity of engineered nanoparticles (NPs) have been conducted in artificial water with well-controlled conditions, which are dramatically different from natural waters with complex compositions. To better understand the fate and toxicity of NPs in the natural water environment, physicochemical transformations of four NPs (TiO2, ZnO, Ag, and carbon nanotubes (CNTs)) and their toxicities towards a unicellular green alga (Chlorella pyrenoidosa) in four fresh water and one seawater sample were investigated. Results indicated that water chemistry had profound effects on aggregation, dissolution, and algal toxicity of the NPs. The strongest homoaggregation of the NPs was associated with the highest ionic strength, but no obvious correlation was observed between the homoaggregation of NPs and pH or dissolved organic matter content of the water samples. The greatest dissolution of ZnO NPs also occurred in seawater with the highest ionic strength, while the dissolution of Ag NPs varied differently from ZnO NPs. The released Zn2+ and especially Ag+ mainly accounted for the algal toxicity of ZnO and Ag NPs, respectively. The NP-cell heteroagglomeration occurred generally for CNTs and Ag NPs, which contributed to the observed nanotoxicity. However, there was no significant correlation between the observed nanotoxicity and the type of NP or the water chemistry. It was thus concluded that the physicochemical transformations and algal toxicities of NPs in the natural water samples were caused by the combined effects of complex water quality parameters rather than any single influencing factor alone. These results will increase our knowledge on the fate and effects of NPs in the aquatic environment.

Effect of natural and synthetic surface coatings on the toxicity of multiwalled carbon nanotubes toward green algae

Ubiquitous dissolved organic matter (DOM) from various sources can interact with discharged multiwalled carbon nanotubes (MWCNTs) and pose distinct effects on the toxicity of MWCNTs to aquatic organisms. This study for the first time compared effects of a natural originated humic acid (HA) and two synthetic surfactants (sodium dodecylbenzenesulfonate – SDBS, octyl phenoxy polyethoxyethanol – TX100) on the toxicity of MWCNTs to a unicellular green alga (Chlorella pyrenoidosa). Algal growth inhibition, cell surface hydrophobicity, oxidative stress, MWCNT-cell agglomeration, and cell morphology change and internalization of MWCNTs were assayed to investigate individual and combined toxicities of MWCNTs and DOMs, and mechanisms underlying different effects of DOMs on the toxicity of MWCNTs were specifically addressed. It is shown that SDBS and TX100 were capable of promoting cell internalization of MWCNTs and triggering higher oxidative stress, and thereby increasing the toxicity of MWCNTs; while HA could alleviate the toxicity of MWCNTs through limiting cell internalization of MWCNTs and reducing oxidative stress. The outcomes of this work shed new light on the assessment of ecological toxicity of discharged nanomaterials.