Microalgal Cells Research Articles

Saccharopolyspora sp. NFXS83 in Marine Biotechnological Applications: From Microalgae Growth Promotion to the Production of Secondary Metabolites.

Marine bacteria are a significant source of bioactive compounds for various biotechnological applications. Among these, actinomycetes have been found to produce a wide range of secondary metabolites of interest. Saccharopolyspora is one of the genera of actinomycetes that has been recognized as a potential source of these compounds. This study reports the characterization and genomic analysis of Saccharopolyspora sp. NFXS83, a marine bacterium isolated from seawater from the Sado estuary in Portugal. The NFXS83 strain produced multiple functional and stable extracellular enzymes under high-salt conditions, showed the ability to synthesize auxins such as indole-3-acetic acid, and produced diffusible secondary metabolites capable of inhibiting the growth of Staphylococcus aureus. Furthermore, when Phaeodactylum tricornutum was co-cultivated with strain NFXS83 a significant increase in microalgae cell count, cell size, auto-fluorescence, and fucoxanthin content was observed. Detailed analysis revealed the presence of clusters involved in the production of various secondary metabolites, including extracellular enzymes, antimicrobial compounds, terpenes, and carotenoids in the genome of strain NFXS83. Ultimately, these findings indicate that Saccharopolyspora sp. NFXS83 has a significant potential for a wide range of marine biotechnological applications.

Comparison of biofloc formation from microalgal cultivation by auto- and bacteria-associated types of flocculation

Microalgal harvesting has still been a challenge to investigators who take their investiment into microalgal production. The cost for microalgal downstream processing is as high as 20% of the total production of biodiesel. Among hundreds of curent methods of biomass harvesting, autoflocculation and bacteria-based aggregation are still being researched and applied in large-scale producuion. This study implemented a comparison of how microalgal cells aggregate large bioflocs according to two types of flocculation. The microalgal autoflocculation was implemented by adding Ca2+ or Mg2+ with an increase of pH to 11, resulting in cell biomass of 13.7 or 15.5 mg/l, respectively. Meanwhile, the bioflocculation under the support of Bacillus subtilis MT300405 and Escherichia coli ATCC 85922 could produce large bioflocs with a cell biomass of 1.5 times higher than the autoflocculation case without the influence of pH. Moreover, images from scanning electron microscopy indicated differences between two types of flocculation. With the presence of bacteria, microalgal cells were more tightly bound by a membrane or a layer of extracellular polimeric substance, inducing to form large bioflocs. This was not found under autoflocculation.

Potential of microalgae Bio-Coke as a sustainable solid fuel alternative to coal coke

Energy and environmental issues have triggered the search for new sources of green energy alternatives in recent years. Biofuel production from renewable sources is widely considered one of the most sustainable alternatives for environmental and economic sustainability. Microalgae are currently being promoted as one of the most promising liquid biofuel feedstocks due to their rapid growth, high lipid production capacity, and carbon–neutral cycle. In this study, whole microalgae cells were utilized as raw material to produce solid biofuel, i.e., Bio-Coke, and this study aimed to investigate the possibility of microalgae Bio-Coke as an alternative to coal coke. The results show that Bio-Coke can be produced from microalgae in the temperature range of 80–100 °C. The apparent density is between 1.253 and 1.261 g/cm3, comparable to the apparent density of lignocellulosic Bio-Coke. Additionally, the calorific value is higher than the calorific value of lignocellulosic Bio-Coke and within the range of the calorific value of subbituminous coal. Therefore, microalgae Bio-Coke can be utilized to replace coal coke usage in the future.

Density and Growth Rate of Nannochloropsis oculata with Different Photoperiods

Nannochloropsis oculata is a type of single-celled or eukaryotic phytoplankton belonging to the class Eustigmatophyceae. This type of microalgae is widely used as natural food for rotifers and fish larvae because it has a high nutritional content. Given this role, many species of Nannochloropsis oculata are cultivated by culture. The success of microalgae culture is influenced by growth factors such as light intensity, CO2, temperature, and nutrition. However, in the process problems often arise regarding the unstable growth of Nannochloropsis oculata. This is usually caused by factors that affect growth, such as light that is not optimal. Based on these problems, it is necessary to conduct research that aims to determine the growth rate of Nannochloropsis oculata with different irradiation treatments. The research method used was an experimental method with 4 treatments i.e., A (24L : 0D), B (12L : 12D), C (18L : 6D), and D (6L : 18D). The results showed that different light exposure period on the density of Nannochloropsis oculata microalgae had no significant effect on their growth rate. Even though the results of statistical tests of photoperiod administration did not affect the production of Nannochloropsis oculata microalgae cell density, the treatment with the dark phase resulted in better growth.

Unveiling the underlying molecular mechanisms of high lutein production efficiency in Chlorella sorokiniana FZU60 under a mixotrophy/photoautotrophy two-stage strategy by transcriptomic, physiological, and biochemical analyses

BackgroundChlorella sorokiniana FZU60 is a promising lutein producing microalga. A mixotrophy/photoautotrophy two-stage strategy can achieve high biomass concentration at stage 1 and high lutein content at stage 2, leading to excellent lutein production efficiency in C. sorokiniana FZU60. However, the underlying molecular mechanisms are still unclear, restraining the further improvement of lutein production.ResultsIn this study, physiological and biochemical analysis revealed that photochemical parameters (Fv/Fm and NPQ) and photosynthetic pigments contents increased during the shift from mixotrophy to photoautotrophy, indicating that photosynthesis and photoprotection enhanced. Furthermore, transcriptomic analysis revealed that the glyoxylate cycle and TCA cycle were suppressed after the shift to photoautotrophy, leading to a decreased cell growth rate. However, the gene expression levels of photosynthesis, CO2 fixation, autophagy, and lutein biosynthesis were upregulated at the photoautotrophy stage, demonstrating that microalgal cells could obtain more precursor to synthesize lutein for enhancing photosynthesis and reducing reactive oxygen species.ConclusionsThe findings help to elucidate the molecular mechanisms for high lutein production efficiency of C. sorokiniana FZU60 under the mixotrophy/photoautotrophy strategy, identify key functional genes responsible for lutein biosynthesis, and shed light on further improvement of lutein production by genetic or metabolic engineering in future studies.

Enhanced VFAs production from microalgal hydrolytic acidification with ultrasonic-alkali pretreatment

Cell disruption to break the rigid algal cell wall was essential to improve the utilization of resources enriched in microalgae. This study aimed to compare the effects of alkali, ultrasound, and the synergistic effect of ultrasonic and alkali on microalgae disruption and preliminarily investigated the synergistic disruption mechanism. The effect of the above methods on the disruption of microalgal cells was quantified by measuring protein and TOC release. Under the optimized conditions of the UA method (initial pH: 12.0, sound intensity: 6 W/mL, 40 min), the protein release was 360.42 mg/g TS, which were 5.6 and 7.1 times higher than those of alkali and ultrasound, respectively. EEMs spectroscopy showed that org-N compounds were mainly released during UA treatment of Chlorella pyrenoidosa (C. pyrenoidosa), with soluble microbial by-product-like compounds predominating. With free radical detection and particle size analysis, it was found that nutrient release occurred mainly during the microalgal bloom dispersion and individual microalgal micro-fragmented phases. The practical applicability of the synergistic strategy was also investigated. Microalgal hydrolytic acidification after UA pretreatment was suitable for VFAs production. Compared to the blank group, the peak VFAs production (392.5 mg COD/g VSS) increased by 200 % and the time reduced from 11 days to 9 days. These results indicated that synergistic disruption pretreatment was expected to improve the performance of microalgal biomass hydrolytic acidification.

A biphasic photobioreactor system for consecutive extraction of lipids and carotenoids from pre-hydrolysed microalgae and evaluation of its biodiesel potential

A green extraction method is developed using partially hydrolysed microalgal cells grown in biocompatible solvent for simultaneous cultivation and extraction of bioproducts from a highly efficient permeabilized microalgal cell with enhanced biomass and lipid content for potential use in biodiesel production. Incomplete digestion of cell wall was achieved by regulating the incubation time of the enzymatic pretreatment of the microalgal cells. 15.77% increase in lipid content was seen when untreated cells were cultured with biocompatible solvent, while cultivation of these enzymatically pretreated cells with biocompatible solvent, the lipid content increased by 53.33% and 22% higher carotenoid content was observed as compared to conventional extraction. The total fatty acids obtained after 1st and 2nd extractions in untreated samples were 67.82%, while those in enzymatically partially digested samples were 91.94%. The untreated and partially enzymatically predigested strain showed suitable properties for quality biodiesel production as per international recommendations. The cost benefit analysis of the overall process showed the use of biocompatible solvent coupled to enzymatically predigested biomass was a favorable option as compared to conventional extraction.

Polarization fingerprint for microalgae classification

Microalgae classification is important for aquatic environment monitoring, but it is difficult in some in-situ cases. The Mueller matrix is known to encode the physical properties including the sophisticated microstructure of microalgae cells. In this paper, the concept of polarization fingerprint based on the Mueller matrix is presented to extract the parameters to classify microalgae. An experimental setup based on the particulate Mueller matrix polarimetry (PMP) is used to measure 25 kinds of microalgae covering seven phyla to form a Mueller matrix dataset. The proposed sixteen polarization parameters with explicit physical meanings and associations with the structural properties are selected to compose the polarization fingerprint. As a result, different microalgae can be effectively classified by the polarization fingerprint and machine learning algorithms. The contribution of the parameters in the polarization fingerprint is analyzed to provide the specific features for microalgae classification, which gives insights into microalgae's exclusive physical properties. The extensibility and flexibility of the polarization fingerprint are discussed. This work shows the polarization fingerprint's power to classify microalgae, which can help retrieve in-situ information on the community structures of microalgae, and further monitor the aquatic environment.

Preparation and Characterization of Microalgae Styrene-Butadiene Composites Using Chlorella vulgaris and Arthrospira platensis Biomass.

The food industry is a high consumer of polymer packing materials, sealing materials, and engineering components used in production equipment. Biobased polymer composites used in the food industry are obtained by incorporating different biogenic materials into the structure of a base polymer matrix. Renewable resources such as microalgae, bacteria, and plants may be used as biogenic materials for this purpose. Photoautotrophic microalgae are valuable microorganisms that are able to harvest sunlight energy and capture CO2 into biomass. They are characterized by their metabolic adaptability to environmental conditions, higher photosynthetic efficiency than terrestrial plants, and natural macromolecules and pigments. The flexibility of microalgae to grow in either low-nutrient or nutrient-rich environments (including wastewater) has led to the attention for their use in various biotechnological applications. Carbohydrates, proteins, and lipids are the main three classes of macromolecular compounds contained in microalgal biomass. The content in each of these components depends on their growth conditions. In general, proteins represent 40-70% of microalgae dry biomass, followed by carbohydrates (10-30%) and lipids (5-20%). A distinctive feature of microalgae cells is the presence of light-harvesting compounds such as photosynthetic pigments carotenoids, chlorophylls, and phycobilins, which are also receiving growing interest for applications in various industrial fields. The study comparatively reports on polymer composites obtained with biomass made of two species of green microalgae: Chlorella vulgaris and filamentous, gram-negative cyanobacterium Arthrospira. Experiments were conducted to reach an incorporation ratio of the biogenic material into the matrix in the 5-30% range, and the resulting materials were characterized by their mechanical and physicochemical properties.

Application of Green Technology to Extract Clean and Safe Bioactive Compounds from Tetradesmus obliquus Biomass Grown in Poultry Wastewater.

Microalgae are capable of assimilating nutrients from wastewater (WW), producing clean water and biomass rich in bioactive compounds that need to be recovered from inside the microalgal cell. This work investigated subcritical water (SW) extraction to collect high-value compounds from the microalga Tetradesmus obliquus after treating poultry WW. The treatment efficiency was evaluated in terms of total Kjeldahl nitrogen (TKN), phosphate, chemical oxygen demand (COD) and metals. T. obliquus was able to remove 77% TKN, 50% phosphate, 84% COD, and metals (48-89%) within legislation values. SW extraction was performed at 170 °C and 30 bar for 10 min. SW allowed the extraction of total phenols (1.073 mg GAE/mL extract) and total flavonoids (0.111 mg CAT/mL extract) with high antioxidant activity (IC50 value, 7.18 µg/mL). The microalga was shown to be a source of organic compounds of commercial value (e.g., squalene). Finally, the SW conditions allowed the removal of pathogens and metals in the extracts and residues to values in accordance with legislation, assuring their safety for feed or agriculture applications.

Algal-algal bioflocculation enhances the recovery efficiency of Picochlorum sp. QUCCCM130 with low auto-settling capacity

Large-scale production of microalgal biomass is still considered non-viable due to the high cost and energy required for harvesting. A fast, cost-effective, and successful harvesting technique has become widely sought after in microalgal biotechnology applications. Algal-algal bioflocculation was adopted for the current study, pH and the ratio between species were selected as two parameters to be optimised. Picochlorum sp. QUCCCM130, Nannochloris sp. QUCCCM31 and Tetraselmis sp. QUCCCM50 presenting a cell size of ∼2 μm, ∼5 μm, and ∼15 μm, respectively, were selected to be subjected to the harvesting optimisation experiments. Results showed that self-settlement capacity increased with cell size and can be indirectly related to a decreased zeta potential of larger cells which enhances the Van der Waals attractive forces. Furthermore, it was noted that pH enhanced the self-settlement capacity of small-sized cells as well that are unable to self-settle. Algal-algal bioflocculation efficiency is dependent on the ratio between species with different sizes, increasing with a higher proportion of larger size microalgal cells. Mixing three microalgae together at pH 10 led to the appearance of large flocs in which the larger cells surrounded the smaller cells. Microscopic observation confirmed that Tetraselmis sp. held the small cells inside the flocs using their flagella. Thus, we can conclude that mixing microalgal cells in a specific ratio and at a specific pH increases the recovery efficiency of small-sized microalgae that can be difficult to harvest, such as Picochlorum sp. QUCCCM130.

Cultivation of Pseudochlorella pringsheimii for biodiesel production in a scalable indoor photobioreactor: case studies from Egypt

BackgroundEnhancement of lipid accumulation is the major strategy to improve the commercial feasibility of microalgae as a source for biodiesel production. Pseudochlorella pringsheimii (Formally was named as Chlorella ellipsoidea) green microalgae strain was chosen with respect to their ability as a potential source to produce high lipids content, could be used for the production of biofuel, which can be an alternative renewable energy source instead of fossil fuels. ResultsInitially, the Pseudochlorella pringsheimii microalgae was evaluated on the basis of tested at Lab scales 2 L by applicable different nutrient individual of N, P, Fe conditions in BBM medium concentrations for choosing the best concentrations induce lipid contents and productivity to cultivate in large scale in the 2000 L PBR. The suitable concentrations of nutrients with highest lipid contents were obtained under deficient of nitrogen (1.25 gL−1, limited N) and phosphorus (0.1 mg L−1, limited P) coupled with high iron concentration (10 mg L, rich Fe) and CO2 (6%). Therefore, their collective of nutrients was applied to culture of microalgae cells at large scale in 2000 L photobioreactor (PBR model), which, this techniques was used to quantify high lipid contents (25% w/w) and high lipid productivity (74.07 mgL−1 day−1). The inducted lipid conversion to biodiesel via transestrification process was 91.54 ± 1.43%. The fatty acid methyl esters (FAMEs profile by means of GC/MS resulted in C16:0, C18:1, C18:2, C18:3 as a main constituents. With regard to physical–chemical property (such as density, kinematic viscosity, gravity, and certain number), the Pseudochlorella pringsheimii biodiesel have biofuel properties, in accordance with appropriate biodiesel properties, as ASTM and EU standards, that thereby referring to high quality biodiesel. ConclusionsPseudochlorella pringsheimii cultured in large scale in photobioreactor under stress condition have a high potential of lipids production with high quality of FAMEs that can be used as a promising biodiesel fuel. It has also a potential to be applied for commercialization based on the techno-economic and environmental impacts. Highlights*Pseudochlorella pringsheimii showed a high potential of lipids 25% lipid accumulation.*Pseudochlorella pringsheimii could be cultured at large scale in potobioreactor, as potential feedstock for biodiesel production.*Bodiesel FAME contains C 16:0, C 18:1 and C 18:2 as a maim FAM.*N, P starvation collective with high Fe3+was the main driver behind lipid accumulation.*Pseudochlorella pringsheimii biodiesel have appropriate biodiesel properties, as ASTM and EU standards.*C. ellipsoidea can be used as a potential feedstock for biodiesel production.

A Review of The Micro-Algae Are Being Harvested to Make Biofuel

Effective harvesting is seen by many researchers as the main obstacle to the commercialization of microalgal biofuel. The small size of micro-algal cells, the cells' similar density to the growth medium, the algae's negative surface charge, and the algae's faster growth rates than terrestrial plants present additional difficulties for harvesting micro-algae. Sedimentation, flocculation, floatation, centrifugation, filtering, or any combination of these procedures can be used to collect algae. The numerous techniques for gathering and dehydrating microalgae for the creation of biofuel are reviewed in this research.

A novel biocompatible polymer derived from D-mannitol used as a vector in the field of genetic engineering of eukaryotic cells

The design and preparation of new vectors to transport genetic material and increase the transfection efficiency continue being an important research line. Here, a novel biocompatible sugar-based polymer derived from D-mannitol has been synthesized to be used as a gene material nanocarrier in human (gene transfection) and microalga cells (transformation process). Its low toxicity allows its use in processes with both medical and industrial applications. A multidisciplinary study about the formation of polymer/p-DNA polyplexes has been carried out using techniques such as gel electrophoresis, zeta potential, dynamic light scattering, atomic force microscopy, and circular dichroism spectroscopy. The nucleic acids used were the eukaryotic expression plasmid pEGFP-C1 and the microalgal expression plasmid Phyco69, which showed different behaviors. The importance of DNA supercoiling in both transfection and transformation processes was demonstrated. Better results were obtained in microalga cells nuclear transformation than in human cells gene transfection. This was related to the plasmid’s conformational changes, in particular to their superhelical structure. It is noteworthy that the same nanocarrier has been used with eukaryotic cells from both human and microalga.

Nanotechnology: An outstanding tool for increasing and better exploitation of microalgae valuable compounds

The earth's limited resources demands our society their optimization so that the population's demands for energy, food, water, and medicines are fulfilled. Moreover, the expanding population, along with the socio-demographic shifts, and the emergence of new diseases, comprise the key challenges of this century. It is well-known that worldwide food and energy demands will duplicate by 2050, a scenario that would lead to the overexploitation of existing traditional animal and plant-based resources and cause adverse environmental impacts. Therefore, it is critical that new strategies should be pilared on sustainable production from alternative sustainable and environmentally friendly sources, to meet our society's long-term needs. Within the past decades, microalgae, as unicellular photosynthetic organisms, have attracted significant attention in various fields, from biofuel production to medical fields. Microalgae exhibit very interesting characteristics, such as their faster growth rate and higher biomass efficiency compared to plants. In addition, microalgae contain valuable bioresources, including lipids, pigments, carbohydrates, proteins, and bioactive compounds such as antioxidant, antibacterial, antiviral, anticancer, regenerative, antihypertensive, neuroprotective, and immunostimulating. However, the level of these compounds can be varied under different cultivation conditions such as nutrient availability, light intensity, CO2 concentration, temperature, and pH. There are various interesting reviews that have focused on different strategies to improve the growth and valuable compounds of microalgae, such as genetic engineering tools. However, recently, nanotechnology emerges as a field that offers novel and efficient methods to improve culturing conditions. To enhance the valuable compounds in microalgae, nanoparticles (NPs) with unique and different physiochemical behaviors are utilized and this review focuses on discussing and providing the state-of-the-art techniques that involve NPs and that are employed to improve microalgae growth rate, light utilization, access to carbon dioxide, and therefore increase the valuable compounds in microalgae cells.

Solid-state fermentation-based enzyme-assisted extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp

Enzymatic treatment of microalgal biomass is a promising approach for extraction of microalgal lipid, but high cost of commercially sourcing enzyme is a major drawback in industrial implementation. Present study involves extraction of eicosapentaenoic acid-rich oil from Nannochloropsis sp. biomass using low cost cellulolytic enzymes produced from Trichoderma reesei in a solid-state fermentation bioreactor. Maximum total fatty acid recovery of 369.4 ± 4.6 mg/g dry weight (total fatty acid yield of 77%) was achieved in 12 h from the enzymatically treated microalgal cells, of which the eicosapentaenoic acid content was 11%. Sugar release of 1.70 ± 0.05 g/L was obtained post enzymatic treatment at 50 °C. The enzyme was reused thrice for cell wall disruption without compromising on total fatty acid yield. Additionally, high protein content of 47% in the defatted biomass could be explored as a potential aquafeed, thus enhancing the overall economics and sustainability of the process.

Environmental Policy to Develop a Conceptual Design for the Water–Energy–Food Nexus: A Case Study in Wadi-Dara on the Red Sea Coast, Egypt

In the next twenty years, the scarcity of food shortage and drinking water will appear in Egypt due to the growth of industries and agriculture. This paper develops a conceptual design of the new technologies in the field of water–energy–food in new cities. Border lines are the internal relationship, external influence, and linkage system evaluation for WEF nexus. The major problems of using fossil energy in desalination are emissions and non-renewability, as well as the preference for dispersed freshwater production instead of concentrated output. The design of a desalination system that is integrated with renewable energies is critical these days. This type of system can also reduce the production of environmental pollutants due to reduced energy consumption and transfer of freshwater. GIS data from the United Nations have confirmed the existence of an underground reservoir in Wadi-Dara that can cultivate 1000 acres using smart farming techniques to reach a circular economy for an integrated solution between the water–energy nexus. The possibility of cultivating a hundred acres in Wadi-Dara on the Red Sea coast exists, through which about one million people could be settled. In this comprehensive review, we conducted a deep study in order to establish a sustainable integrated lifestyle in the Dara Valley region in terms of the availability of potable water, clean energy, and agriculture. Sustainable integrated solutions were conducted for seawater desalination using beach sand filtration wells as a pretreatment for seawater using renewable energy, e.g., wind energy (18% wind turbines), and photovoltaic panels (77% PV panels). Strategic food will be cultivated using smart farming that includes an open ponds cultivation system of microalgal cells to synthesis (5.0% of bio-fuel (. Aqua agriculture and aquaponics will cultivate marine culture and integrate mangrove, a shrimp aquaculture. A municipal waste water treatment is conceived for the irrigation of shrubby forests and landscapes. Mixotrophic cultures were explored to achieve a sustained ecological balance. Food, poultry and animal waste management, as well as a cooker factory, were included in the overall design. The environmental impact assessment (EIA) study shows a low risk due to anticipated net zero emissions, a 75% green city, and optimal waste recycling. This research assists in combining research efforts to address the challenging processes in nexus research and build resilient and sustainable water, energy, and food systems.

Assessment of the Tolerance of a Chlorophyte Desmodesmus to CuO-NP for Evaluation of the Nanopollution Bioremediation Potential of This Microalga.

Broad application of CuO nanoparticles (CuO-NP) for industrial and household purposes leads to a continuous increase in their discharge to, and, hence, ever-increasing environmental hazards for aquatic ecosystems. Microalgae-based technologies hold promise for bioremediation of diverse hazardous micropollutants (HMP), including NP, from wastewater. In this study, we tested the ability of the green microalga Desmodesmus sp. to accumulate CuO-NP or their components. We also assessed the tolerance of this microalga to the environmentally relevant concentrations of CuO-NP. Using scanning electron microscopy, we demonstrated that the average size of CuO-NP was 50-100 nm, and their purity was confirmed with elemental composition analysis. Tests of the colloidal suspensions of CuO-NP showed that the hydrodynamic diameter of CuO-NP and their aggregates was below 100 nm. Flow cytometry analysis showed that CuO-NP at a concentration of 100 µg L-1 slightly inhibited the viability of microalgae cells and led to an increase in their oxidative stress. The assessment of the condition of photosystem II showed that CuO-NP exert a multifaceted effect on the photosynthetic apparatus of Desmodesmus sp., depending on the concentration of and the exposure to the CuO-NP. Desmodesmus sp. turned to be relatively tolerant to CuO-NP. In addition, the ICP-MS method revealed increased bioaccumulation of copper by microalgae cells in the experimental groups. The outcomes of this study indicate that the Desmodesmus sp. has a significant potential for bioremoval of the copper-based nanostructured HMP from an aquatic environment.

Effect of ultrasound on Pseudoneochloris marina and Chlorella zofingiensis growth

The present work evaluated the ultrasound (US) effects on the growth of Pseudoneochloris marina and Chlorella zofingiensis. For P. marina, US treatment did not increase cell proliferation and reduced cell density when used for 60 min (exponential phase, for 5 days), indicating a possible occurrence of cell damage. For C. zofingiensis, the application of discontinuous US for 10 min resulted in an increase of 65 % in biomass concentration compared to the control. These distinct behaviors indicate that microalgae species react differently to physical stimuli. After US treatment, a reduction of carotenoid, chlorophyll, lipid and protein concentrations was observed, which may be related to changes in the metabolic pathways to produce these compounds. Overall, the results of the present study show the potential of discontinuous US to enhance microalgae cell proliferation.

Sublethal exposure to agrochemicals impairs zooplankton ability to face future global change challenges

Intensive agriculture is characterized by the application of multiple stressors that damage aquatic systems. Currently, ecotoxicological evaluations are considered insufficient to understand the environmental risks of stressor mixtures and their consequences in ecosystems. In addition, future global change scenarios could alter the predicted effects of agrochemicals in aquatic systems based on single exposures, making it necessary to consider the history of environmental disturbances that may result in vulnerability to subsequent environmental changes. The objectives of this study were to induce disturbance histories by exposure to sublethal glyphosate concentrations in microcosms and to assess whether this disturbance results in vulnerable populations using Daphnia magna as the target species. Populations were considered vulnerable if their sensitivity to new stressors (inanition, temperature and salinity) was higher than that of undisturbed populations. To induce disturbance history, microcosm aquatic communities (two cladocerans and one microalgae) were exposed to two glyphosate sublethal concentrations (below the No Observed Effect Concentration, NOEC values for D. magna, 0.1 and 1 mg L−1) in microcosms under controlled conditions in a culture chamber for 48 days. After this period, no significant differences were observed with respect to the control microcosms in the selected parameters (cladoceran abundance, microalgae cell abundance, microalgae colony formation, pH and dissolved oxygen). To test vulnerability, our target D. magna populations, which were previously exposed to different glyphosate treatments, were subjected to inanition, elevated temperature and salinity. Our results showed that D. magna populations with disturbance history performed worse in all the scenarios compared to the populations from undisturbed conditions. These results underscore the need to study how environmental disturbance history influences population responses to new and future stressors. Moreover, our findings raise concern regarding the sublethal effects of pesticides on aquatic populations.