Potential of microalgae as biopesticides to contribute to sustainable agriculture and environmental development

Comprehensive assessment of microalgal-based treatment processes for dairy wastewater

The dairy industry is becoming one of the biggest sectors within the global food industry, and these industries use almost 34% of the water. The amount of water used is governed by the production process and the technologies employed in the plants. Consequently, the dairy industries generate almost 0.2-10 L of wastewater per liter of processed milk, which must be treated before being discharged into water bodies. The cultivation of microalgae in a mixotrophic regime using dairy wastewater enhances biomass growth, productivity, and the accumulation of value-added product. The generated biomass can be converted into biofuels, thus limiting the dependence on petroleum-based crude oil. To fulfill the algal biorefinery model, it is important to utilize every waste stream in a cascade loop. Additionally, the harvested water generated from algal biomass production can be recycled for further microalgal growth. Economic and sustainable wastewater management, along with proper reclamation of nutrients from dairy wastewater, is a promising approach to mitigate the problem of water scarcity. A bibliometric study revealing limited work on dairy wastewater treatment using microalgae for biofuel production. And, limited work is reported on the pretreatment of dairy wastewater via physicochemical methods before microalgal-based treatment. There are still significant gaps remains in large-scale cultivation processes. It is also crucial to discover robust strains that are highly compatible with the specific concentration of contaminants, as this will lead to increased yields and productivity for the targeted bio-product. Finally, research on reutilization of culture media in photobioreactor is necessary to augument the productivity of the entire process. Therefore, the incorporation of the microalgal biorefinery with the wastewater treatment concept has great potential for promoting ecological sustainability.

Resources recovery from domestic wastewater by a combined process: anaerobic digestion and membrane photobioreactor

Anaerobic and membrane technologies are a promising combination to decrease the energy consumption associated with wastewater treatment, allowing the recovery of resources: organic matter as biomethane, nutrient assimilation by microalgae and reclaimed water. In this study, domestic wastewater was treated using a combination of an upflow anaerobic sludge blanket sludge reactor (UASB) and a membrane photobioreactor (MPBR). The outdoor facilities were operated continuously for three months under unfavourable environmental conditions such as lack of temperature control, winter season with lower solar irradiation and lower daylight hours which was a challenge for the present work, not previously described. The energetic valorisation of the organic matter present in the wastewater by biomethane produced in the UASB would contribute to reducing overall facilities' energy requirements. The ultrafiltration (UF) membrane facilitated the harvesting of biomass, operating at 10 L·h-1·m-2 during the experimental period. Although the main contribution to fouling was irreversible, chemical cleanings were not necessary due to effective fouling control, which prevented the final TMP from exceeding 25 kPa. In addition, microalgae-bacterial consortium developed without prior inoculation were harvested from the MPBR using membrane assistance. The obtained biomass was also successfully tested as a biostimulant for corn germination/growth, as well as a biopesticide against Rhizoctonia solani and Fusarium oxysporum.

Microbial Bioherbicides Based on Cell-Free Phytotoxic Metabolites: Analysis and Perspectives on Their Application in Weed Control as an Innovative Sustainable Solution

Weeds cause significant agricultural losses worldwide, and herbicides have traditionally been the main solution to this problem. However, the extensive use of herbicides has led to multiple cases of weed resistance, which could generate an increase in the application concentration and consequently a higher persistence in the environment, hindering natural degradation processes. Consequently, more environmentally friendly alternatives, such as microbial bioherbicides, have been sought. Although these bioherbicides are promising, their efficacy remains a challenge, as evidenced by their limited commercial and industrial production. This article reviews the current status of microbial-based bioherbicides and highlights the potential of cell-free metabolites to improve their efficacy and commercial attractiveness. Stirred tank bioreactors are identified as the most widely used for production-scale submerged fermentation. In addition, the use of alternative carbon and nitrogen sources, such as industrial waste, supports the circular economy. Furthermore, this article discusses the optimization of downstream processes using bioprospecting and in silico technologies to identify target metabolites, which leads to more precise and efficient production strategies. Bacterial bioherbicides, particularly those derived from Pseudomonas and Xanthomonas, and fungal bioherbicides from genera such as Alternaria, Colletotrichum, Trichoderma and Phoma, show significant potential. Nevertheless, limitations such as their restricted range of action, their persistence in the environment, and regulatory issues restrict their commercial availability. The utilization of cell-free microbial metabolites is proposed as a promising solution due to their simpler handling and application. In addition, modern technologies, including encapsulation and integrated management with chemical herbicides, are investigated to enhance the efficacy and sustainability of bioherbicides.

Chlorella vulgaris and Tetradesmus obliquus Protect Spinach (Spinacia oleracea L.) against Fusarium oxysporum

Chlorella vulgaris and Tetradesmus obliquus were tested as biocontrol agents against the phytopathogenic fungus Fusarium oxysporum. This evaluation was conducted through in vitro and in vivo trials with spinach (Spinacia oleracea L.). The in vitro trials showed that C. vulgaris and T. obliquus were able to inhibit the phytopathogen, showing a similar inhibitory effect to that of the positive controls (Rovral, BASF® and Biocontrol T34, Biocontrol Technologies® S.L.). C. vulgaris aqueous suspensions at 3.0 g L-1 led to a hyphal growth of 0.55 cm, each corresponding to a reduction of 63% of fungal growth. With T. obliquus, the hyphal growth was 0.53 cm when applied at a concentration of 0.75 g L-1, having an inhibition of fungus growth of 64%. Thereafter, these results were validated in an in vivo trial on spinach using the same controls. The results revealed a lower severity and disease incidence and a reduction in the disease's AUDPC (area under the disease progress curve) when spinach was treated with the microalgae suspensions. Overall, these findings highlight the potential of C. vulgaris and T. obliquus suspensions as promising biocontrol agents against F. oxysporum in spinach when applied through irrigation.

Effect of pretreated and anaerobically digested microalgae on the chemical and biochemical properties of soil and wheat grown on fluvisol

In this study, the effects of the potential application of digestate as an agricultural fertiliser obtained from anaerobically digested microalgae treated by three pretreatment methods, namely alkaline hydrogen peroxide (AHP), high temperature and pressure (HTP), and hydrodynamic cavitation (HC) on some properties of soil, and wheat growth and yield were investigated. For this purpose, pretreated and anaerobically digested microalgae digestates alone or together with diammonium phosphate (DAP) as a chemical fertiliser were applied to soil for wheat growth. The highest dosage of AHP pretreated digestate combined with a half dose of DAP applied to soil was rich in nutrients as 0.25%N and 7.19 mg kg-1 compared to all groups. The properties of the soils were enhanced by applying the highest dosage (0.06 g kg-1) of microalgae digestate combined with a half dose of DAP. 0.02 g kg-1 dosage of HC pretreated digestate combined with a half dose of DAP also greatly improved nitrogen use efficiency indices by up to 104%. The soils' enzyme activities increased in wheat growth experiments by applying either raw or pretreated microalgae digestates. The soils' β-glycosidase, alkaline phosphatase, and urease enzyme activities increased to 1.38 mg pNP g-1 soil, 4.91 mg pNP g-1 soil, and 2.27 mg NH4-N 100 g-1 soil respectively by the application of highest dosage of HC pretreated digestate. The digestates did not have a toxic effect on wheat growth, it was determined that applied pretreatment processes did not cause significant changes in wheat plant height or wet and dry weight.

Neochloris aquatica induces larval mortality, molting defects, and unstable flightless adults in the Asian tiger mosquito

The Asian tiger mosquito, Aedes albopictus, is a highly invasive and aggressive species capable of transmitting a large number of etiological agents of medical and veterinary importance, posing a high risk for the transmission of emerging viruses between animals and humans. In this work, we evaluated the mosquitocidal activity of Neochloris aquatica against A. albopictus throughout its development and analyzed whether this effect was potentiated when the microalga was cultivated under stress conditions due to nutrient deprivation. Our results suggest that N. aquatica produces metabolites that have negative effects on these insects, including larval mortality, interruption of pupal development, and incomplete emergence of adults when fed on microalgae in the larval stages. When microalgae were cultured under stress conditions, an increase in molting defects was recorded, and the number of healthy adults emerged drastically decreased. Histological studies revealed severe signs of total disintegration of different tissues and organs in the thorax and abdomen regions. The muscles and fat bodies in the midgut and foregut were severely distorted. In particular, larval intestinal tissue damage included vacuolization of the cytoplasm, destruction of brush border microvilli, and dilation of the intercellular space, which are distinctive morphological characteristics of apoptotic cells. Evidence suggests that N. aquatica produces metabolites with mosquitocidal effects that affect development and, therefore, the ability to vector etiological agents of medical and veterinary importance.

A step forward in sustainable pesticide production from Amphidinium carterae biomass via photobioreactor cultivation with urea as a nitrogen source

This study addresses the problem of replacing nitrate and ammonium with urea as a greener nitrogen source in the mass cultivation of the microalga Amphidinium carterae for the development of amphidinol-based phytosanitary products. To solve this problem, a nuclear magnetic resonance assisted investigation evaluated the effect of nitrogen sources on growth and metabolic profiles in photobioreactors. Urea-fed cultures exhibited growth kinetics comparable to nitrate-fed cultures (µmax = 0.30 day-1, Pbmax = 43 mgL-1day-1). Urea-fed cultures had protein, lipid, and carbohydrate contents of 39.5%, 14.5%, and 42.4%, respectively, while nitrate-fed cultures had 27.9 %, 17.5% and 48.1%, respectively. Metabolomics revealed nitrogen source-dependent metabotypes and a correlation between amphidinols and polyunsaturated fatty acids. The amphidinol-to-nitrogen yield coefficient in urea-fed cultures (135 mg/g) was approximately 2.5 times higher than in nitrate-fed cultures. The potent antiphytopathogenic activity exhibited by extracts from urea-fed cultures underscores the potential of urea as a sustainable nitrogen source in microalgae-based biorefineries.

Use of micro and macroalgae extracts for the control of vector mosquitoes

Mosquitoes are one of the most dangerous vectors of human diseases such as malaria, dengue, chikungunya, and Zika virus. Controlling these vectors is a challenging responsibility for public health authorities worldwide. In recent years, the use of products derived from living organisms has emerged as a promising approach for mosquito control. Among these living organisms, algae are of great interest due to their larvicidal properties. Some algal species provide nutritious food for larvae, while others produce allelochemicals that are toxic to mosquito larvae. In this article, we reviewed the existing literature on the larvicidal potential of extracts of micro- and macroalgae, transgenic microalgae, and nanoparticles of algae on mosquitoes and their underlying mechanisms. The results of many publications show that the toxic effects of micro- and macroalgae on mosquitoes vary according to the type of extraction, solvents, mosquito species, exposure time, larval stage, and algal components. A few studies suggest that the components of algae that have toxic effects on mosquitoes show through synergistic interaction between components, inhibition of feeding, damage to gut membrane cells, and inhibition of digestive and detoxification enzymes. In conclusion, algae extracts, transgenic microalgae, and nanoparticles of algae have shown significant larvicidal activity against mosquitoes, making them potential candidates for the development of new mosquito control products.

The combined effects of microbial insecticides and sodium chloride on the development and emergence of Chironomus xanthus

BACKGROUND

Freshwater organisms are facing increasing salinity levels, not only due to natural environmental processes, but also human activities, which can cause several physiological adaptations to osmotic stress. Additionally, these organisms might also have to deal with contamination by microbial insecticides. Our main goal was to use Chironomus xanthus to assess the chronic effects of increasing the salinity and commercial formulations of the microbial insecticides based on Bacillus thuringiensis subs. kurstaki (Btk) and Beauveria bassiana (Bb) as active ingredients, respectively.

RESULTS

A significant interaction of growth was observed between the biopesticide based on Bb and NaCl on the larvae of C. xanthus. Single exposure to NaCl and each one of the formulations demonstrated deleterious impacts not only on larval development, but also on the emergence success and emergence time of this nontarget insect, with potential consequences for freshwater ecosystems due to cascading effects.

CONCLUSION

The chronic effects induced by both bioinsecticides show that these formulations can have environmental impacts on nontarget freshwater insects. © 2023 Society of Chemical Industry.

The Potential of Allelochemicals from Microalgae for Biopesticides

Improvements in agricultural productivity are required to meet the demand of a growing world population. Phytopathogens, weeds, and insects are challenges to agricultural production. The toxicity and widespread application of persistent synthetic pesticides poses a major threat to human and ecosystem health. Therefore, sustainable strategies to control pests are essential for agricultural systems to enhance productivity within a green paradigm. Allelochemicals are a less persistent, safer, and friendly alternative to efficient pest management, as they tend to be less toxic to non-target organisms and more easily degradable. Microalgae produce a great variety of allelopathic substances whose biocontrol potential against weeds, insects, and phytopathogenic fungi and bacteria has received much attention. This review provides up-to-date information and a critical perspective on allelochemicals from microalgae and their potential as biopesticides.

Microalgae as next generation plant growth additives: Functions, applications, challenges and circular bioeconomy based solutions

Sustainable agriculture practices involve the application of environment-friendly plant growth promoters and additives that do not negatively impact the health of the ecosystem. Stringent regulatory frameworks restricting the use of synthetic agrochemicals and the increase in demand for organically grown crops have paved the way for the development of novel bio-based plant growth promoters. In this context, microalgae biomass and derived agrochemicals offer novel sources of plant growth promotors that enhance crop productivity and impart disease resistance. These beneficial effects could be attributed to the presence of wide range of biomolecules such as soluble amino acid (AA), micronutrients, polysaccharides, phytohormones and other signaling molecules in microalgae biomass. In addition, their phototrophic nature, high photosynthetic efficiency, and wide environmental adaptability make them an attractive source of biostimulants, biofertilizers and biopesticides. The present review aims to describe the various plant growth promoting metabolites produced by microalgae and their effects on plant growth and productivity. Further, the effects elicited by microalgae biostimulants with respect to different modes of applications such as seed treatments, foliar spray and soil/root drenching is reviewed in detail. In addition, the ability of microalgae metabolites to impart tolerance against various abiotic and biotic stressors along with the mechanism of action is discussed in this paper. Although the use of microalgae based biofertilizers and biostimulants is gaining popularity, the high nutrient and water requirements and energy intensive downstream processes makes microalgae based technology commercially unsustainable. Addressing this challenge, we propose a circular economy model of microalgae mediated bioremediation coupled with biorefinery approaches of generating high value metabolites along with biofertilizer applications. We discuss and review new trends in enhancing the sustainability of microalgae biomass production by co-cultivation of algae with hydroponics and utilization of agriculture effluents.

The bioherbicidal potential of isolated fungi cultivated in microalgal biomass

This study evaluated the bioherbicidal potential of wild fungi grown on microalgal biomass from the digestate treatment of biogas production. Four fungal isolates were used and the extracts were evaluated for the activity of different enzymes and characterized by gas chromatography coupled with mass spectrometry. The bioherbicidal activity was assessed by application on Cucumis sativus, and the leaf damage was visually estimated. The microorganisms showed potential as agents producing an enzyme pool. The obtained fungal extracts presented different organic compounds, most acids, and when applied to Cucumis sativus, showed high levels of leaf damage (80-100 ± 3.00%, deviation relative to the observed average damage). Therefore, the microbial strains are potential biological control agents of weeds, which, together with the microalgae biomass, offer the appropriate conditions to obtain an enzyme pool of biotechnological relevance and with favorable characteristics to be explored as bioherbicides, addressing aspects within the environmental sustainability.

Robust fractional control based on high gain observers design (RNFC) for a Spirulina maxima culture interfaced with an advanced oxidation process

In this article, the theory of fractional control and state estimation applied to biological science is studied, particularly in hybrid wastewater treatment. For nonlinear systems with stable and known states, an interconnected fractional robust control design with high gain state estimation is proposed to generate a control insensitive to nutritional perturbations originated by an advanced oxidation process in a microalgae culture. An online study is proposed for the mineralization of glyphosate and its feedback in a microalgae cultivation process where through the designed control the light dynamics is manipulated to robustly and automatically regulate the biomass signal provided by an analog sensor and nutrient estimation via state observers. In the literature, there are few results developed with real-time results. This work is a multidisciplinary study with online results where the performance and improvement of the proposed complex process are concluded.

Microalgal remediation and valorisation of polluted wastewaters for zero-carbon circular bioeconomy

Overexploitation of natural resources to meet human needs has considerably impacted CO₂ emissions, contributing to global warming and severe climatic change. This review furnishes an understanding of the sources, brutality, and effects of CO₂ emissions and compelling requirements for metamorphosis from a linear to a circular bioeconomy. A detailed emphasis on microalgae, its types, properties, and cultivation are explained with significance in attaining a zero-carbon circular bioeconomy. Microalgal treatment of a variety of wastewaters with the conversion of generated biomass into value-added products such as bio-energy and pharmaceuticals, along with agricultural products is elaborated. Challenges encountered in large-scale implementation of microalgal technologies for low-carbon circular bioeconomy are discussed along with solutions and future perceptions. Emphasis on the suitability of microalgae in wastewater treatment and its conversion into alternate low-carbon footprint bio-energies and value-added products enforcing a zero-carbon circular bioeconomy is the major focus of this review.

Stochastic Ex-Ante LCA under Multidimensional Uncertainty: Anticipating the Production of Undiscovered Microalgal Compounds in Europe

Due to their biodiversity, microalgae represent a promising source of high-value compounds that bioprospecting is aiming to reveal. Performing an ex-ante Life Cycle Assessment (LCA) to anticipate and potentially minimize the environmental burden associated with the European production of a bioprospected microalgal compound is subject to substantial and multi-factorial uncertainty as the compound remains undiscovered. Given that any microalgal strain could potentially host the compound of interest, the ex-ante LCA should consider this bioprospecting uncertainty together with the uncertainty on the technology and the production mix. Using a parameterized cultivation simulation and consequential LCA model and an extensive stochastic pseudo Monte Carlo approach, we define and propagate techno-operational, bioprospecting, and production mix uncertainties for a microalgal compound being currently bioprospected in Europe. We perform global sensitivity analysis using different sampling strategies to identify the main contributors to the total output variance. Overall, the uncertainty propagation allowed us to define and analyze the probabilistic scope for the potential environmental impacts in the emerging production of high-value microalgal compounds in Europe based on current knowledge. These findings can support policy-making as well as actors in the microalgal sector toward technological paths with lower environmental impact.

High-Throughput Sequencing as a Tool for the Quality Control of Microbial Bioformulations for Agriculture

Microbial bioformulations, due to their positive impact on the growth and development of plants, as well as the absence of harmful effects on the environment and humans, have a vast potential for mass introduction into agriculture. Assessing the quality of bioformulations, especially complex ones, is a difficult task. In this study, we show that high-throughput sequencing can be an effective tool for the quality control and safety of microbial bioformulations. By the method of high-throughput sequencing on the MiSeq platform, we studied 20 samples of commercially available microbial bioformulations. In parallel with this, bioformulations were studied by classical microbiological methods. The analysis showed the presence of extraneous undeclared bacterial genera by the manufacturer. Only 10% of the bioformulations fully corresponded to the commercial composition, and another 10% of the bioformulations did not contain the bacteria declared by the manufacturer in their composition at all. The bacterial composition of 80% of the bioformulations partially corresponded to the composition indicated on the package. The most frequent microbial bioformulations contaminants were Enterococcus, Lactobacillaceae, Klebsiella, Escherichia-Shigella and Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium. Universal methods for the quality control of bioformulations are needed. The advantages of high-throughput sequencing for the evaluation of bioformulations are considered in this work.

Microalgae Polysaccharides: An Alternative Source for Food Production and Sustainable Agriculture

Carbohydrates or polysaccharides are the main products derived from photosynthesis and carbon fixation in the Calvin cycle. Compared to other sources, polysaccharides derived from microalgae are safe, biocompatible, biodegradable, stable, and versatile. These polymeric macromolecules present complex biochemical structures according to each microalgal species. In addition, they exhibit emulsifying properties and biological characteristics that include antioxidant, anti-inflammatory, antitumor, and antimicrobial activities. Some microalgal species have a naturally high concentration of carbohydrates. Other species can adapt their metabolism to produce more sugars from changes in temperature and light, carbon source, macro and micronutrient limitations (mainly nitrogen), and saline stress. In addition to growing in adverse conditions, microalgae can use industrial effluents as an alternative source of nutrients. Microalgal polysaccharides are predominantly composed of pentose and hexose monosaccharide subunits with many glycosidic bonds. Microalgae polysaccharides can be structural constituents of the cell wall, energy stores, or protective polysaccharides and cell interaction. The industrial use of microalgae polysaccharides is on the rise. These microorganisms present rheological and biological properties, making them a promising candidate for application in the food industry and agriculture. Thus, microalgae polysaccharides are promising sustainable alternatives for potential applications in several sectors, and the choice of producing microalgal species depends on the required functional activity. In this context, this review article aims to provide an overview of microalgae technology for polysaccharide production, emphasizing its potential in the food, animal feed, and agriculture sector.

Climate-Resilient Microbial Biotechnology: A Perspective on Sustainable Agriculture

We designed this review to describe a compilation of studies to enlighten the concepts of plant–microbe interactions, adopted protocols in smart crop farming, and biodiversity to reaffirm sustainable agriculture. The ever-increasing use of agrochemicals to boost crop production has created health hazards to humans and the environment. Microbes can bring up the hidden strength of plants, augmenting disease resistance and yield, hereafter, crops could be grown without chemicals by harnessing microbes that live in/on plants and soil. This review summarizes an understanding of the functions and importance of indigenous microbial communities; host–microbial and microbial–microbial interactions; simplified experimentally controlled synthetic flora used to perform targeted operations; maintaining the molecular mechanisms; and microbial agent application technology. It also analyzes existing problems and forecasts prospects. The real advancement of microbiome engineering requires a large number of cycles to obtain the necessary ecological principles, precise manipulation of the microbiome, and predictable results. To advance this approach, interdisciplinary collaboration in the areas of experimentation, computation, automation, and applications is required. The road to microbiome engineering seems to be long; however, research and biotechnology provide a promising approach for proceeding with microbial engineering and address persistent social and environmental issues.

Antifungal potential, chemical composition of Chlorella vulgaris and SEM analysis of morphological changes in Fusarium oxysporum

In pursuit of an environmentally benign fungicide alternative, the current study explored the antifungal activity of Chlorella vulgaris extracts against six plant pathogenic fungi (in vitro). The well diffusion agar method was used to investigate the growth inhibition of Fusarium oxysporum, Fusarium sp., Fusarium solani, A. flavus, A. niger, and A. alternata using the three C. vulgaris extracts viz. methanol (CvME), acetone (CvAE), and diethyl ether (CvDE). Different concentrations of CvDE were also investigated against F. oxysporum. The morphological modifications in F. oxysporum treated with CvDE (5 mg/kg) were studied using SEM and the chemical composition of CvDE was also determined by GC–MS analysis. All extracts, with the exception of A. alternata, were found to be effective in inhibiting the growth of plant pathogenic fungi. The CvDE extract, followed by CvME and CvAE, was found to be efficient against tested fungi. The CvDE was most effective against F. oxysporum with a 73.3% growth inhibition. The effects of various CvDE concentrations on F. oxysporum were found to be dosage dependent. The SEM micrograph revealed that CvDE-treated F. oxysporum had substantially less conidia than the control. The CvDE treatment damaged the mycelial structure as well. Major chemical components detected in CvDE were Heptaldehyde (15.7%), Octadecenoic acid, methyl ester (12.6%), Hexadecanoic acid (12%), 3-Decyn-2-Ol (10.98%), (E)-3,7,11,15-tetramethylhexadec-2-ene (9.76%), heptadecane-1,2,3,4,5-pentol (8.7%), Docosane, 4-methyl (7.28%).

Screening and evaluation of different algal extracts and prospects for controlling the disease vector mosquito Culex pipiens L

Continual application of synthetic insecticides in controlling mosquito larvae has resulted in several problems as build-up of mosquito resistance beside to negative impacts on human health and environment. Discovering new and affordable bio-insecticidal agents with high efficiency, cost effective and target specific become a crucial need. The current study assessed the larvicidal activity of eight methanolic algal extracts belong to three different algal divisions against the 3^rd larval instar of Culex pipiens L. (Diptera: Culicidae). Comparative studies showed that four species of red and green algal extracts exhibited good larvicidal activity. Galaxaura elongata and Jania rubens (Rhodophyta), Codium tomentosum and Ulva intestinales (Chlorophyta) showed higher larvicidal potencies than Padina boryana, Dictyota dichotoma, and Sargassum dentifolium (Phaeophyta) and Gelidium latifolium (Rhodophyta). The maximum level of toxicity was achieved by exposure to G. elongata extract with LC₅₀ (31.13 ppm), followed by C. tomentosum (69.85 ppm) then J. rubens (84.82 ppm) and U. intestinalis (97.54 ppm), while the lowest toxicity exhibited by G. latifolium (297.38 ppm) at 72 h post- treatment. The application of LC₅₀ values of G. elongate, J. rubens, C. tomentosum, and U. intestinalis extracts affected the activities of antioxidant enzymes viz. superoxide dismutase, catalase and glutathione peroxidase as oxidative stress markers. An increase of antioxidant enzymes activities was recorded. Therefore, a significant elimination of free radicals, causing toxic effects. Overall, this study casts light on the insecticidal activity of some algal extracts, suggesting the possibility of application of these bio- agents as novel and cost- effective larvicides.

Advances in microalgal research for valorization of industrial wastewater

This review article focuses on recent updates on remediation of industrial wastewater (IWW) through microalgae cultivation. These include how adding additional supplements of nutrient to some specific IWWs lacking adequate nutrients improving the microalgae growth and remediation simultaneously. Various pretreatments strategy recently employed for IWWs treatment other than dealing with microalgae was discussed. Various nutrient-rich IWW could be utilized directly with additional dilution, supplement of nutrients and without any pretreatment. Recent advances in various approaches and new tools used for cultivation of microalgae on IWW such as two-step cultivation, pre-acclimatization, novel microalgal-bioelectrical systems, integrated catalytic intense pulse-light process, sequencing batch reactor, use of old stabilized algal-bacterial consortium, immobilized microalgae cells, microalgal bacterial membrane photobioreactor, low-intensity magnetic field, BIO_ALGAE simulation tool, etc. are discussed. In addition, biorefinery of microalgal biomass grown on IWW and its end-use applications are reviewed.

Microalgae as biostimulants: a new approach in agriculture

This review aims to elucidate the state of the art of microalgae-based biostimulants as a tool in agriculture by summarizing the biologically active compounds factors that influence the use of microalgae biostimulants and their application methods in the field. Additionally, we examined the factors that support the use of microalgal biostimulants to face abiotic and biotic stress in crop plants. The use of microalgae in crop production and the benefits of seed preparation, foliar application, soil drenching, and hydroponic treatments were discussed. Furthermore, the use of these biostimulants in crop plants and their multiple benefits such as, better rooting, higher crop, fruit yields, drought and salinity tolerance, photosynthetic activity and pathogen resistance was thoroughly presented. The present situation of microalgal biostimulants and their difficulties in the market was analyzed, as well as the perspectives of their use. However, data shows that microalgal derived biostimulants can be used as an alternative for the protection of crops and plant growth regulators and play a significant key role in increasing the levels of production, yield and health of crops. Special interest needs to focus on investigating more microalgae species and their biological active compound factors, due to the largely untapped field. Perspectives regarding future research lines and development priorities were included.

What do patents tell us about microalgae in agriculture?

Microalgae have been used widely as a biological source for several industries, such as biofuel, pharmaceutical and food. Recently, the agricultural industry has also began using microalgae as an alternative source for sustainable products to replace agrochemicals. Due to the lack of scientific articles in this research area, the objective of this study was to search for applications of microalgae and to characterize its use in agriculture using the patent documents available in three patent databases, World Intellectual Property Organization (WIPO), European Patent Office (EPO) and Brazilian Institute of Industrial Property (INPI). The search was carried out using the keyword “microalgae” and applying the filter for International Patent Classification (IPC) code “A01N” which corresponds to patents related to agriculture and cultivation of microalgae. Our patent database search returned 669 documents and 132 patents were selected for the study based on their abstracts. The first patent was registered in 1982 and described the use of microalgae Chlorella extract as a plant growth promoter. After that, no patent was registered for 15 years. From 2005 to 2014, only seven patents were found. However, the scenario changed from 2015 when the number of patents increased mainly in the United States, China and Europe. The patent analysis showed several applications for microalgae in the agricultural sector, such as plant growth promotion, biofertilization, plant disease control, weed management, and post-harvest quality. This review confirmed the increasing interest in microalgae-derived products in agriculture and the value of using patent documents to assess innovative areas.

Effect of storage on plant biostimulant and bioactive properties of freeze-dried Chlorella vulgaris biomass

Microalgae are potential plant biostimulants and biocontrol agents. A major hurdle towards their commercialization is the production of large volumes of biomass at the correct time of year. Secondary metabolites are unstable and the "shelf-life" of bioactive microalgal biomass needs to be investigated. The aim of the study was to investigate the effects of storage conditions on freeze-dried microalgae to determine how long the biomass retained its growth promoting and bioactive properties under various temperature and light conditions. Chlorella vulgaris biomass was stored in the dark at - 70 °C, 10 °C, and 25 °C and in the light at 25 °C. Samples were tested every 3-4 months for 15 months. Storage time significantly influenced the rate of change in the bioactivity in the C. vulgaris biomass with storage temperature also having some effect. Rooting activity decreased in the mungbean rooting assay over time up to 12 months and then increased slightly. Antimicrobial activity increased against Staphylococcus aureus and Escherichia coli for up to 12 months and then declined. Antioxidant activity measured in the DPPH assay remained relatively stable for up to 12 months and then significantly decreased with longer storage. The change in bioactivity over time was attributed to the gradual breakdown of the rigid cell wall of C. vulgaris, thereby improving extraction efficiency but exposing the secondary metabolites to oxygen, thus quickening their degradation. Biomass produced for commercial purposes requires preliminary validation as the results of the present study showed that bioactive compounds are susceptible to degradation over time.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10811-021-02596-9.

Ecotoxicological evaluation of fruit extracts from yerba mate progenies (Ilex paraguariensis a St-Hil.): a natural biopesticide

This study evaluated the biocidal activity of aqueous fruit extracts from Ilex paraguariensis progenies at different ripening stages in two ecotoxicity assays using Pomacea canaliculata juveniles and Danio rerio larvae. Mutagenicity was verified by the Salmonella/microsome assay (TA 98 and TA 100) in the presence and absence of hepatic metabolism in vitro. The results showed that the snails were more sensitive than the larvae to the P.1 progeny extracts in all three evaluated ripening stages. P.3 progeny extracts were the most toxic to Danio rerio larvae after 96 hours of exposure. The toxicity results indicate that the progenies' selection influenced the metabolic contents present in the fruits in all ripening stages over time, indicating high molluscicidal activity for the P.1 progeny. In the Salmonella/microsome assays, the semi-ripe and ripe extracts from progenies P.1 and P.3 showed mainly base pair substitution mutation in assays with metabolism, but at higher doses than the toxic concentrations detected for Danio rerio or Pomacea canaliculata. Therefore, the toxicological investigation of the progenies' extracts can be interesting, given the selection of plant materials influenced the response of the bioassays.

Systematic Investigation of the Effects of Seven Plant Extracts on the Physiological Parameters, Yield, and Nutritional Quality of Radish (Raphanus sativus var. sativus)

The modern agricultural sector faces the challenge of addressing the needs of the fast-growing global population. This process should be both high-yielding and sustainable, without creating risks for the environment and human health. Therefore, natural products are gaining attention in the production of safe and nutritious food. In a systematic effort to develop affordable and effective biostimulants, we examined the impact of botanical extracts on the growth and physiological parameters of radish plants under field conditions. Ultrasound-assisted extraction, mechanical homogenization, and water were used for the production of potential plant-based biostimulants. Foliar applications of the bio-products, developed and used in our study, have led to an increase in the examined parameters (total yield, dry weight, photosynthetic pigments, vitamin C, nitrates, and micro- and macroelements). A decrease in the total phenolic compounds content was also noted, as well as a varied impact on the steam volatile compounds, fatty acids, sterol, and glucosinolates composition. The most beneficial effects on radish, in terms of physiological and biochemical properties, were found in groups treated with extracts based on the common dandelion, valerian, and giant goldenrod. This innovative approach presented in our study could provide a valuable tool for sustainable horticultural production.

An Overview of Some Biopesticides and Their Importance in Plant Protection for Commercial Acceptance

Biopesticides are natural, biologically occurring compounds that are used to control various agricultural pests infesting plants in forests, gardens, farmlands, etc. There are different types of biopesticides that have been developed from various sources. This paper underscores the utility of biocontrol agents composed of microorganisms including bacteria, cyanobacteria, and microalgae, plant-based compounds, and recently applied RNAi-based technology. These techniques are described and suggestions are made for their application in modern agricultural practices for managing crop yield losses due to pest infestation. Biopesticides have several advantages over their chemical counterparts and are expected to occupy a large share of the market in the coming period.

Emerging nanobiotechnology in agriculture for the management of pesticide residues

Utilization of pesticides is often necessary for meeting commercial requirements for crop quality and yield. However, incessant global pesticide use poses potential risks to human and ecosystem health. This situation increases the urgency of developing nano-biotechnology-assisted pesticide formulations that have high efficacy and low risk of side effects. The risks associated with both conventional and nanopesticides are summarized in this review. Moreover, the management of residual pesticides is still a global challenge. The contamination of soil and water resources with pesticides has adverse impact over agricultural productivity and food security; ultimately posing threats to living organisms. Pesticide residues in the eco-system may be treated via several biological and physicochemical processes, such as microbe-based degradation and advanced oxidation processes. With these issues in mind, we present a review that explores both existing and emerging techniques for management of pesticide residues and environmental risks. These techniques can offer a sustainable solution to revitalize the tarnished water/soil resources. Further, state-of-the-art research approaches to investigate biotechnological alternatives to conventional pesticides are discussed along with future prospects and mitigation techniques are recommended.

Seriphidium brevifolium essential oil: a novel alternative to synthetic insecticides against the dengue vector Aedes albopictus

The Aedes albopictus mosquito is a vector of several deadly diseases of humans and domesticated animals. Usually, synthetic insecticides are used for mosquito control. The excessive use of synthetic insecticides is hazardous for humans and the environment. Therefore, there is a need to develop environment-friendly and novel mosquito larvicides. In the current study, we evaluated larvicidal and bite protection properties of Seriphidium brevifolium essential oil (SBEO) and its active constituents against this mosquito. SBEO and its active constituents, α, β-thujone, and limonene, were toxic to A. albopictus, with LC50 values of 21.43, 45.99, 47.38, and 49.46 μg/mL. The cream formulation of EO at 5 % (w/v) provided complete protection against mosquito bites until 70 min after application. Among the EO constituents tested, α and β-thujone showed considerable protections against mosquito bites but lower as compared with the whole oil. Furthermore, 1:1 combinations of active constituent α-thujone and β-thujone and 1:1:1 combinations of α-thujone, β-thujone, and limonene displayed a synergistic effect against the larvae. Particularly, the EO and its active constituents were safer to Poecilia reticulata a mosquito predator, with LC50 ranging from 3934.33 to 14,432.11 μg/mL. Our current study indicated that SBEO and some of its constituents can be used for the control of A. albopictus mosquito, as a novel alternative to hazardous synthetic insecticides and to overcome the problem of increasing insecticides resistance.