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

Microalgal density assessment based on quantum-dot light-emitting diodes and intelligent image edge detection

This study proposes an approach involving image capture, recognition, and processing using quantum dots for light conversion, which emit blue, green, orange, and red light. Microalgae species of Nannochloropsis sp. and Chaetoceros sp. are selected for observation. In addition to color differences and brightness distribution, an optimized composite detecting indicator (OCDI) is introduced, which combines six conventional edge detection indicators with adjustable weight coefficients. The performance obtained with the quantum-dot illumination system is compared with results obtained under non-specific lighting conditions by evaluating image edge characteristics, average brightness, color differences, and light intensity measurements. When evaluating OCDI under different colors, the proposed method achieves an accuracy (η) of 0.99 and a coefficient of determination (R2) of 0.99, as compared to conventional manual counting method. The proposed microalgal density assessment method, characterized by high accuracy, flexibility, and environmental friendliness, demonstrates potential applicability in smart marine agriculture and digital marine monitoring.

Review of biological algal fertilizer technology: Alleviating salinization, sequestering carbon, and improving crop productivity

Periphyton-based biofertilizer have a high potential for soil remediation, particularly for controlling soil salinization. This global environmental problem leads to low soil utilization and insufficient crop yields. Efficient and sustainable methods of managing saline soils are needed to reduce salinization and improve soil fertility and crop quality. Traditional methods such as physical mulching and chemical amendments, while improving soil conditions, exhibit limited effectiveness and may damage soil structure. This study aims to evaluate the feasibility of algae-based fertilizers in remediating saline-alkali soils and improving crop performance. The review delves into the and application prospects of algae-based fertilizers, highlighting their potential from both sustainable development and economic perspectives. It further advocates integrating other emerging technologies with the production and application of algae-based fertilizers to address the increasingly severe challenges posed by degraded soil resources and environmental instability. The review found that algal fertilizers are more environmentally friendly than traditional chemical fertilizers but are not inferior in function. This approach offers more efficient and sustainable solutions for managing saline-alkaline soils and effectively achieves sustainable agricultural production. Furthermore, it is necessary to conduct experimental research and monitoring evaluations of algal fertilizers to formulate scientific and rational fertilization plans to meet the increasingly serious challenges facing soil resources and unstable environments. The findings of this study will provide theoretical and technical support for using algae biofertilizers for soil remediation, improving crop quality and sequestering carbon.

Utilization of residues from microalgal industries for agricultural practices: A comprehensive review

Global consumptions of fertilizers and freshwater have been continuously growing due to increased food demand, leading to great concerns on food security. Bio-based resilient nutrient resources such as microalgae-derived waste biomass and wastewater have gained great attention as alternative fertilizer resources because they contain key nutrients (nitrogen and phosphorus), organic compounds (acting as soil conditioner, growth stimulators), and micronutrients. Thus, microalgae-derived solid and liquid fertilizers have great potential in promoting plant growth in soil and/or hydroponic farming, controlling release of nutrients to avoid nutrient leaching and volatilization, and facilitating to achieve circular economy in microalgal industries. However, several challenges, such as imbalanced nutrient element ratios, causes of heavy metal accumulation and increased pH/conductivity, may limit their wide applications. Several recent-published review articles have documented the application of fresh microalgal biomass as fertilizer sources via direct use and conversion methods or recycling cultivation medium for microalgal growth, but no review has been conducted on utilization of microalgal processing wastewater and biomass residues for agriculture practices. Herein, this article provides a comprehensive review on the processes relating to recovery of resources (water, nutrients, valuable plant growth compounds) from microalgae processing wastewater and biomass residues generated in microalgal biorefinery industries, and identifies the key factors that are associated with the resource recovery efficiency and their effects on plant growth.

Cyanobacterium Nostoc species mitigate soybean cyst nematode infection on soybean by shaping rhizosphere microbiota

Soybean cyst nematode (SCN, Heterodera glycines Ichinohe) is the most devastating and yield-limiting pathogen that threatens soybean production globally. Sustainable SCN disease management strategies are needed. In this study, a cyanobacterial strain was isolated from SCN-infected soybean soil and identified as Nostoc punctiforme using the cyanobacterial 16S rRNA gene sequence. When susceptible soybean plants were grown in the SCN-inoculated soil, N. punctiforme inoculants significantly reduced the total number of SCN eggs and second-stage juveniles (J2s), compared to the control with SCN inoculation only. Further microbial analysis showed that N. punctiforme inoculants changed the bacterial and fungal communities in the soybean rhizospheres and significantly increased the relative abundance of several bacterial and fungal species with potential nematicidal activities, suggesting the changes of soybean rhizosphere microbiota may partially contribute to the activity of N. punctiforme inoculants against SCN. However, N. punctiforme inoculants did not directly induce soybean defense reactions against SCN. Thus, N. punctiforme may be a potential microbial source against SCN invasion in soybean.

How to improve the potential of microalgal biostimulants for abiotic stress mitigation in plants?

Abiotic stress is among the most critical factors limiting crop productivity worldwide and its importance is further exacerbated by climate change. In recent years, microalgal biostimulants have gained attention for their potential to enhance plant resilience towards abiotic stress. However, significant hurdles still persist, particularly regarding the unknown modes of action of microalgal biostimulants, which is a concern for stringent regulatory requirements and product reliability. The aim of this review is to improve the potential of microalgal biostimulants for abiotic stress mitigation in plants by addressing different key parameters shaping the efficacy of microalgal biostimulants, encompassing cultivation approaches, extraction techniques, and application methods. Furthermore, it also highlights how microalgal biostimulants modulate plant morphology, physiology and biochemistry under drought, salinity, and heat stress-three predominant stressors anticipated to intensify under climate change. Notably, these biostimulants consistently enhance drought stress tolerance by improving biomass accumulation, nutrient uptake, and water use efficiency through enhanced photosynthesis and stomatal regulation. These effects are largely driven by the accumulation of osmoprotectants and antioxidant compounds. In contrast, salt stress mitigation is highly species-dependent, with some microalgae enhancing stress tolerance through osmoprotectant and antioxidant accumulation, while others reduce these compounds, potentially lowering stress perception via unknown mechanisms. Despite the significance of the abiotic stress, heat stress mitigation by microalgal biostimulants remains an underexplored research area. Additionally, indirect applications of microalgae-ranging from biotechnological innovations to desalination-underscore the broader potential of these organisms in agricultural resilience. Collectively, this review identifies three key gaps in the existing literature-the diversity gap, the practical gap, and the research gap-while outlining promising avenues for future research in microalgal biostimulant development.

Effects of Microalgae as Biostimulants on Plant Growth, Content of Antioxidant Molecules and Total Antioxidant Capacity in Chenopodium quinoa Exposed to Salt Stress

Chenopodium quinoa Willd. is a halophytic plant valued for its nutritional and nutraceutical properties, as well as its adaptability to diverse soil and climatic conditions. Biostimulant application enhances plant quality and resilience under adverse environmental conditions. The effects of microalgae extracts (Ettlia pseudoalveolaris and Chlorella vulgaris) and salt stress (NaCl 100, 200, 300 mM) were evaluated on 7-day-old seedlings of two quinoa varieties, 'Tunkahuan' and 'Regalona'. The analysis focused on the content of antioxidant molecules (total phenolics and flavonoids), total antioxidant capacity (measured by DPPH, 2,2-Diphenyl-1-picrylhydrazyl, and FRAP, Ferric Reducing Antioxidant Power, assays), reactive oxygen species (ROS), the levels of lutein, β-carotene, chlorophyll a and b. Microalgae extracts and salt stress treatments significantly increased antioxidant molecules in both quinoa varieties. The highest antioxidant activity, measured by the DPPH assay, was observed in 'Regalona', while a dose-dependent increase in antioxidant capacity, by the FRAP assay, was evident in 'Tunkahuan' treated with Ettlia. ROS level was reduced by Ettlia in 'Tunkahuan' but not in 'Regalona'. Pigment content increased with higher salt concentrations but decreased with the addition of biostimulants. These findings suggest that the application of microalgae extracts enhances bioactive compounds, improving salinity resistance and increasing the nutraceutical value of quinoa sprouts.

Biopriming of Cucumis sativus L. Seeds with a Consortium of Nitrofixing Cyanobacteria Treated with Static Magnetic Field

The growing demand for sustainable agriculture necessitates innovative strategies to enhance crop productivity while minimizing environmental impact. This study explores the biopriming potential of Cucumis sativus L. seeds using extracts derived from a consortium of nitrofixing cyanobacteria Nostoc commune, Calothrix sp., and Aphanothece minutissima subjected to static magnetic field (SMF) treatments. The cyanobacterial consortia were exposed to SMF at varying magnetic inductions (40-50 mT and 100-200 mT), followed by extract preparation and application as biopriming agents. Results demonstrated significant improvements in key seedling growth parameters, including root and stem length, vigor index I, and fresh biomass. The consortium treated with 40-50 mT SMF showed the most pronounced growth-stimulating activity, suggesting enhanced bioactive compound production under this treatment that might be related to auxin biosynthesis. Biopriming with cyanobacterial extracts maintained a balanced nutritional uptake and plant health, as indicated by stable fresh weight dry weight ratios. These findings highlight the potential of SMF-enhanced cyanobacterial consortia as biopriming agents for horticultural crops. Future research should elucidate the underlying modes of action and optimize conditions for broader crop applications.

Stepwise processing of Chlorella sorokiniana confers plant biostimulant that reduces mineral fertilizer requirements

We developed a stepwise method to transform Chlorella sorokiniana microalgal biomass into a potent biostimulant. The method, including maceration, high-pressure homogenization, and enzymatic hydrolysis, preserves the bioactive properties of the biomass as a biostimulant while minimizing plant inhibitory effects. Fractions were characterized individually, and optimal concentrations were determined using a rapid Arabidopsis root assay. A blend of optimal concentrations of fractions was identified as the most stimulating extract, increasing the root elongation by 25 %. When applied to tomato plants and monitored using high-throughput plant phenotyping, the blend displayed a 25 % reduction in mineral fertilizer use. Metabolomic analysis of the tomato plants showed significantly enhanced carbon and nitrogen metabolism in the leaves. Our findings indicate that the stepwise processing not only produces an effective biostimulant but also generates substantial residual biomass for a potential multiproduct biorefinery approach that can improve the overall techno-economic outlook.

Microalgae and microbial inoculant as partial substitutes for chemical fertilizer enhance Polygala tenuifolia yield and quality by improving soil microorganisms

Excessive utilization of chemical fertilizers degrades the quality of medicinal plants and soil. Bio-organic fertilizers (BOFs) including microbial inoculants and microalgae have garnered considerable attention as potential substitutes for chemical fertilizer to enhance yield. In this study, a field experiment was conducted to investigate the effects of BOF partially substituting chemical fertilizer on the growth and quality of medicinal plant Polygala tenuifolia. The growth parameters, bioactive component contents, soil properties and composition of rhizosphere microorganisms were measured. The results indicated that substituting 40% of chemical fertilizer with microalgae showed the most pronounced growth-promoting effect, leading to a 29.30% increase in underground biomass and a 19.72% increase in 3,6'-disinapoylsucrose (DISS) content. Substituting 20% of chemical fertilizer with microalgae improved soil quality, significantly increasing soil organic matter content by 15.68% (p<0.05). Microalgae addition significantly affected the rhizosphere bacterial community composition of P. tenuifolia, reducing the relative abundance of Cladosporium by 33.33% and 57.93%, while increasing the relative abundance of Chloroflexi by 31.06% and 38.27%, under 20% and 40% chemical fertilizer reduction, respectively. The relative abundance of Chloroflexi positively correlated with both the underground biomass and DISS content (p<0.05), indicating that microalgae may stimulate Chloroflexi species associated with carbon cycling, thereby enhancing soil fertility, nutrient absorption, and ultimately leading to increased biomass accumulation and production of bioactive components in P. tenuifolia. In addition, there was no significant difference in underground growth and bioactive component contents between reduced chemical fertilizer dosage combined with solid microbial inoculant (SMI) and polyglutamic microbial inoculant (PMI), compared with 100% chemical fertilizer. Correlation analysis revealed that PMI could increase soil phosphorus availability through Streptomyces recruitment. In conclusion, our findings demonstrated that bio-organic fertilizers can partially substitute chemical fertilizer to improve soil properties and microorganisms, enhancing the growth and quality of P. tenuifolia. This provides a theoretical basis for increasing medicinal plant productivity under chemical fertilizer reduction.

A critical review on the symbiotic effect of bacteria and microalgae on treatment of sewage with biofertilizer production

Wastes like sewage, kitchen and industrial are the major sources of environmental pollution and health hazards. Sewage contains 99.9% water and 0.1% solid waste including urinal waste and faecal matter alongwith large amounts of nitrate, nitrite, ammonium and phosphate ions. Sewage may also contain a variety of harmful contaminants like analgesics, antihypertensive drugs, antibiotics, dioxin, furans, polychlorinated biphenyls, chlorinated hydrocarbon pesticides, chlorine derivatives and plasticizers etc. making it more harmfull to environment and public health. Hence, sewage must be adequately treated by an effective process before its final discharge into the environment. Biological treatment of sewage is an emerging idea in recent years, which has diverse economic and environmental advantages. Sewage treatment by bacteria and microalgae has numerous advantages as it removes various excessive nutrients from waste with large biomass production and also prevents the utilization of toxic chemicals in conventional treatment process. Microalgae-bacterial biomass have potential to be used as biofertilizers, bio-stimulants and bio-seed primers in agricultural field as these contain various biologically active substances like polysaccharides, carotenoids, free fatty acids, phenols, and terpenoids. This review paper mainly discussing the sewage characteristics and different kinds of organic and inorganic pollutants it contained alongwith its harmfull impacts on environment and public health. It also deals the different conventional as well as emerging treatment technologies and different factors affecting the treatment efficiency. In addition, the utilization of developed microalgal and bacterial biomass as biofertilizer and its effects on crop plant alongwith future prospects has been also discussed in detail.

Employing microalgae cultivation on fruits and vegetable peel waste to produce biofuel, lutein, and biochar concurrently with an "Agro to Agro" algae biorefinery approach

The aim of the current investigation is to explore the novel application of pumpkin, papaya, and orange peels as growth substrates for microalgae cultivation, with the overarching goal of advancing a sustainable "Agro to Agro" biorefinery paradigm. The research evaluates the integration of waste management practices into microalgal production, optimizing growth parameters to maximize output. Optimal concentrations of 2.8 mg L-1 for orange peels, 35.5 mg L-1 for papaya peels, and 35.5 mg L-1 for pumpkin peels were identified, alongside a light intensity of 163.7 µmol m-2 s-1 and a nitrogen concentration of 0.8 g L-1. Under these conditions, Chlorella sorokiniana demonstrated peak biomass production of 3.16 g L-1, lipid productivity of 1.55 g L-1, and carotenoid productivity of 9.18 mg L-1, additionally, yielding significant amounts of palmitic acid (47.9%) and lutein. The study further explored the conversion of residual microalgae into biochar, with optimal pyrolysis conducted at 350 °C. The as-synthesized biochar was utilized effectively as a soil amendment for cultivating Vigna radiata. The present study underscores the viability of a closed-loop biorefinery approach, demonstrating the recycling of pumpkin, papaya, and orange peels as effective substrates for microalgae cultivation and subsequent biochar conversion for potential industrial applications. The promising results of the study advocate to the feasibility of this integrated model for sustainable future.

Efficacy of foliar application of Chlorella vulgaris extract on chemical composition and biological activities of the essential oil of spearmint (Mentha spicata L.)

The microalgal have an essential role in agriculture, where they are used as biofertilizers. This study aimed to determine the effect of C. vulgaris extract on the chemical composition and biological activities of the Essential Oil (EO) of Mentha spicata. The extract of C. vulgaris was prepared and applied at three different concentrations (50, 75, and 100 %). The EOs of M. spicata were analyzed by gas chromatography-mass spectrometry (GC-MS). The DPPH radical scavenging capability and Ferric Reducing Antioxidant Power (FRAP) techniques were used to assess the antioxidant activity of EOs. The antimicrobial activity of EO was evaluated using the microdilution method against Staphylococcus aureus. The results of GC-MS analysis of EOs identified 46 components, with Carvone (77.5-65.4 %), Limonene (10.31-6.9 %), β-elemene (1.56-0.98 %), and Caryophyllene (10.92-4.77 %) being the predominant constituents. From the highest concentration ranged from 100 % C. vulgaris extract to control respectively, yield and EO content ranged from 171.24 to 131.74 g/m2 and 0.34 to 0.18 %, respectively; Antioxidant activity by DPPH and FRAP methods varied from 1.56 to 4.45 mg/mL, and 405.63 to 68.68 μMFe2+/g, respectively; the Minimum Inhibitory Concentrations (MIC) ranged from 2.4 to 9.6 mg/mL in various treatments. The results indicated that the C. vulgaris extract significantly increased the yield, EO%, Carvone, Limonene, and antioxidant and antibacterial activities compared to the control. The extract of C. vulgaris showed promise as a biofertilizer to enhance the yield, chemical composition, and biological activities of M. spicata.

Exploring the versatility of Porphyridium sp.: A comprehensive review of cultivation, bio-product extraction, purification, and characterization techniques

Interest in red microalgae of the Porphyridium genus has surged due to their richness in phycobiliproteins, polyunsaturated fatty acids, and sulfated polysaccharides. These biomasses and their derivatives find applications across food, feed, nutraceutical, pharmaceutical, and cosmetic industries. A deeper understanding of their properties and extraction methods is essential to optimize downstream processing. This paper comprehensively reviews Porphyridium sp., focusing on cultivation techniques, bioproduct extraction, purification, and characterization. It delves into protein, lipid, and polysaccharide extraction, considering the influence of culture conditions on biomass yield. Various methods like chromatography, electrophoresis, and membrane-based techniques for cell lysis and bioproduct recovery are explored, highlighting their pros and cons. By offering diverse insights, this review aims to inspire innovative research and industry progress in red microalgae biotechnology, contributing to sustainable solutions across sectors.

Mitigation of Salt Stress in Lactuca sativa L. var. Gentile Rossa Using Microalgae as Priming Agents

Using renewable biomass in agriculture, particularly microalgae as a biostimulant, offers economic and environmental sustainability benefits by reducing costs, improving nutrient cycling, and enhancing water use efficiency. Microalgae contain bioactive compounds that boost crop tolerance to environmental stresses, including salinity. Saline soils, characterized by elevated sodium chloride (NaCl) levels, negatively impact many crops, resulting in low productivity and high remediation costs. Therefore, this study evaluates the biostimulant properties of a microalgae-based commercial preparation (MR) on lettuce (Lactuca sativa L.) plants grown hydroponically and exposed to saline stress. The extract was chemically characterized through elemental analysis, lipid composition (gas chromatography with flame ionization detector-GC-FID), the determination of functional groups (Fourier Transformed Infrared-FT-IR), structure (1H,13C Nuclear Magnetic Resonance-NMR), with their hormone-like activity also assessed. Lettuce plants were treated with or without the microalgae blend, in combination with 0, 50 mM, or 100 mM NaCl. The contents of nutrients, soluble proteins, chlorophylls, and phenols, as well as the lipid peroxidation, antioxidants and root traits of lettuce plants, were estimated. The microalgae applied to salt-stressed plants resulted in a significant increase in biomass, protein, and chlorophyll contents. Additionally, significant effects on the secondary metabolism and mitigation of salinity stress were observed in terms of increased phenol content and the activity of antioxidant enzymes, as well as decreased lipid peroxidation. The potassium (K+) content was increased significantly in plants treated with 100 mM NaCl after addition of microalgae, while the content of sodium (Na+) was concurrently reduced. In conclusion, our results demonstrate that using microalgae can be a potent approach for improving the cultivation of Lactuca sativa L. under saline stress conditions.

Improving Undernutrition with Microalgae

Undernutrition is an important global health problem, especially in children and older adults. Both reversal of maternal and child undernutrition and heathy ageing have become United Nations-supported global initiatives, leading to increased attention to nutritional interventions targeting undernutrition. One feasible option is microalgae, the precursor of all terrestrial plants. Most commercially farmed microalgae are photosynthetic single-celled organisms producing organic carbon compounds and oxygen. This review will discuss commercial opportunities to grow microalgae. Microalgae produce lipids (including omega-3 fatty acids), proteins, carbohydrates, pigments and micronutrients and so can provide a suitable and underutilised alternative for addressing undernutrition. The health benefits of nutrients derived from microalgae have been identified, and thus they are suitable candidates for addressing nutritional issues globally. This review will discuss the potential benefits of microalgae-derived nutrients and opportunities for microalgae to be converted into food products. The advantages of microalgae cultivation include that it does not need arable land or pesticides. Additionally, most species of microalgae are still unexplored, presenting options for further development. Further, the usefulness of microalgae for other purposes such as bioremediation and biofuels will increase the knowledge of these microorganisms, allowing the development of more efficient production of these microalgae as nutritional interventions.

Growth Characteristics of a Desmodesmus Species from the San Antonio Springs and Its Short-Term Impact on Soil Microbial Dynamics

A new Desmodesmus species was isolated from the largest of the San Antonio Springs, the Blue Hole, in San Antonio, Texas, and characterized for its potential applications in sustainable agriculture. The xenic isolate (XB) was established by enrichment and subcultured to produce the axenic isolate (AxB), which was identified based on morphological features and DNA profiling, confirming its close phylogenetic relationship with Desmodesmus spp. Growth characteristics, biomass composition, and pigment profiles were assessed for both the xenic and axenic isolates along with their growth in saline conditions and a range of seasonal Texas temperatures. Both Desmodesmus XB and Desmodesmus AxB exhibited optimal growth at 25 °C as well as robust growth at 37 °C and in weakly saline media (5 g/kg NaCl). Biomass analysis revealed levels of carbohydrates, proteins, lipids, chlorophylls, and carotenoids comparable to other desmids and pigment profiles supported the Desmodesmus classification. Soil studies demonstrated the persistence of Desmodesmus XB and influence on microbial activity, indicating the potential of this isolate for agricultural applications such as soil remediation.

Hydroponics with Microalgae and Cyanobacteria: Emerging Trends and Opportunities in Modern Agriculture

The global population is expected to reach 9.5 billion, which means that crop productivity needs to double to meet the growing population's food demand. Soil degradation and environmental factors, such as climate events, significantly threaten crop production and global food security. Furthermore, rapid urbanization has led to 55% of the world's population migrating to cities, and this proportion is expected to increase to 75% by 2050, which presents significant challenges in producing staple foods through conventional hinterland farming. Numerous studies have proposed various sustainable farming techniques to combat the shortage of farmable land and increase food security in urban areas. Soilless farming techniques such as hydroponics have gained worldwide popularity due to their resource efficiency and production of superior-quality fresh products. However, using chemical nutrients in a conventional hydroponic system can have significant environmental impacts, including eutrophication and resource depletion. Incorporating microalgae into hydroponic systems as biostimulants offers a sustainable and ecofriendly approach toward circular bioeconomy strategies. The present review summarizes the plant growth-promoting activity of microalgae as biostimulants and their mechanisms of action. We discuss their effects on plant growth parameters under different applications, emphasizing the significance of integrating microalgae into a closed-loop circular economy model to sustainably meet global food demands.

Reduction of Oxygen Production by Algal Cells in the Presence of O-Chlorobenzylidene Malononitrile

Chemical compounds, such as the CS gas employed in military operations, have a number of characteristics that impact the ecosystem by upsetting its natural balance. In this work, the toxicity limit and microorganism's reaction to the oxidative stress induced by O-chlorobenzylidenemalonitrile, a chemical found in CS gas, were assessed in relation to the green algae Chlorella pyrenoidosa. A number of parameters, including the cell growth curve, the percent inhibition in yield, the dry cell weight, the percentage viability and productivity of algal biomass flocculation activity, and the change in oxygen production, were analyzed in order to comprehend the toxicological mechanisms of O-chlorobenzylidenemalonitrile on algal culture. Using fluorescence and Fourier transform infrared spectroscopy (FTIR), the content of chlorophyll pigments was determined. The values obtained for pH during the adaptation period of the C. pyrenoidosa culture were between 6.0 and 6.8, O2 had values between 6.5 and 7.0 mg/L, and the conductivity was 165-210 µS/cm. For the 20 µg/mL O-chlorobenzylidenemalonitrile concentration, the cell viability percentage was over 97.4%, and for the 150 µg/mL O-chlorobenzylidenemalonitrile concentration was 74%. The ECb50 value for C. pyrenoidosa was determined from the slope of the calibration curve; it was estimated by extrapolation to the value of 298.24 µg/mL. With the help of this study, basic information on the toxicity of O-chlorobenzylidenemalonitrile to aquatic creatures will be available, which will serve as a foundation for evaluating the possible effects on aquatic ecosystems. The management of the decontamination of the impacted areas could take the results into consideration.

Valorization of treated swine wastewater and generated biomass by microalgae: Their effects and salt tolerance mechanisms on wheat seedling growth

The extensive use of mineral fertilizers has a negative impact on the environment, whereas wastewater and microalgal biomass can provide crops with nutrients such as nitrogen, phosphorus, and potassium, and have the potential to be used as a source of fertilizers in circular agriculture. In this study, a step-by-step resource utilization study of algae-containing wastewater generated from microalgae treatment of swine wastewater was carried out. When wheat seedlings were cultivated in the effluent after microalgae separation, the root fresh weight, seedling fresh weight, and total seedling length were increased by 3.44%, 14.45%, and 13.64%, respectively, compared with that of the algae-containing wastewater, and there was no significant difference in seedling fresh weight, total seedling length, maximum quantum yields of PSII photochemistry (Fv/Fm), and performance index (PIABS) from that of the Hogland solution group, which has the potential to be an alternative liquid fertilizer. Under salt stress, microalgae extract increased the contents of GA3, IAA, ABA, and SA in wheat seedlings, antioxidant enzymes maintained high activity, and the PIABS value increased. Low-dose microalgae extract (1 mL/L) increased the root fresh weight, seedling fresh weight, longest seedling length, and total seedling length by 30.73%, 31.28%, 16.43%, and 28.85%, respectively. Algae extract can act as a plant biostimulant to regulate phytohormone levels to attenuate the damage of salt stress and promote growth.

Using microalgae to reduce the use of conventional fertilizers in hydroponics and soil-based cultivation

The intensive use of agrochemicals has led to nutrient loss, greenhouse gas emissions, and resource depletion, thus the development of sustainable agricultural solutions is required. Microalgal biomass has the potential to provide nutrients such as nitrogen, phosphorus, and potassium, along with various plant growth promoters, to enhance crop productivity and impart disease resistance. This study provides a comprehensive assessment of the potential applications of microalgal extracts and biomass in the contexts of seed germination, hydroponic systems, and soil-based crop cultivation. The results revealed that the extracts from Chlorella sp. and Anabaena sp. have no significant impact on the germination of wheat seeds. High concentrations of Chlorella sp. and Anabaena sp. cell extracts in hydroponics enhanced the length of cucumber seedling stems by 81.7 % and 58.3 %, respectively. Additionally, the use of microalgal cell extracts hindered root elongation while stimulating the growth of lateral and fibrous roots. Furthermore, the study compared the performance of 5 different fertilizers: 1) inorganic fertilizer (IF), 2) organic fertilizer (OF), 3) microalgae-based biofertilizer (MF), 4) inorganic fertilizer + microalgae-based biofertilizer (IM), 5) organic fertilizer + microalgae-based biofertilizer (OM). The findings indicate that the plant growth and soil physicochemical properties in the groups supplied with different fertilizers are comparable and significantly higher than those in the control group. The levels of protein, chlorophyll A, and chlorophyll B in the MF group increased significantly by 40 %, 29.2 %, and 33.5 %, respectively, compared to the control group. However, it remained notably lower compared to groups supplied with inorganic and organic fertilizers (p < 0.05). Combining microalgae with organic fertilizer can simultaneously enhance the yield and quality of Chinese cabbage, representing a promising source of crop nutrition. In conclusion, this study suggests that it is promising to use microalgae to reduce the use of conventional fertilizers in hydroponics and soil-based cultivation.

Comparison of plant biostimulating properties of Chlorella sorokiniana biomass produced in batch and semi-continuous systems supplemented with pig manure or acetate

Microalgae-derived biostimulants provide an eco-friendly biotechnology for improving crop productivity. The strategy of circular economy includes reducing biomass production costs of new and robust microalgae strains grown in nutrient-rich wastewater and mixotrophic culture where media is enriched with organic carbon. In this study, Chlorella sorokiniana was grown in 100 l bioreactors under sub-optimal conditions in a greenhouse. A combination of batch and semi-continuous cultivation was used to investigate the growth, plant hormone and biostimulating effect of biomass grown in diluted pig manure and in nutrient medium supplemented with Na-acetate. C. sorokiniana tolerated the low light (sum of PAR 0.99 ± 0.18 mol/photons/(m2/day)) and temperature (3.7-23.7° C) conditions to maintain a positive growth rate and daily biomass productivity (up to 149 mg/l/day and 69 mg/l/day dry matter production in pig manure and Na-acetate supplemented cultures respectively). The protein and lipid content was significantly higher in the biomass generated in batch culture and dilute pig manure (1.4x higher protein and 2x higher lipid) compared to the Na-acetate enriched culture. Auxins indole-3-acetic acid (IAA) and 2-oxindole-3-acetic acid (oxIAA) and salicylic acid (SA) were present in the biomass with significantly higher auxin content in the biomass generated using pig manure (> 350 pmol/g DW IAA and > 84 pmol/g DW oxIAA) compared to cultures enriched with Na-acetate and batch cultures (< 200 pmol/g DW IAA and < 27 pmol/g DW oxIAA). No abscisic acid and jasmonates were detected. All samples had plant biostimulating activity measured in the mungbean rooting bioassay with the Na-acetate supplemented biomass eliciting higher rooting activity (equivalent to 1-2 mg/l IBA) compared to the pig manure (equivalent to 0.5-1 mg/l IBA) and batch culture (equivalent to water control) generated biomass. Thus C. sorokiniana MACC-728 is a robust new strain for biotechnology, tolerating low light and temperature conditions. The strain can adapt to alternative nutrient (pig manure) and carbon (acetate) sources with the generated biomass having a high auxin concentration and plant biostimulating activity detected with the mungbean rooting bioassay.

Dietary solutions for aluminum embryotoxicity: A study in Danio rerio using spirulina and okra-spirulina diets

Aluminum (Al) is a versatile element commonly employed in various industries and water treatment processes. However, its presence in aquatic ecosystems can elicit adverse effects on organisms, particularly the Danio rerio fish species. Aluminum exposure has been associated with a spectrum of issues, ranging from oxidative stress to behavioral anomalies, reproductive disruptions, and morphological alterations in these organisms. This research aimed to assess the impact of aluminum chloride (AlCl3) on D. rerio embryos and explore strategies to mitigate its effects. Three dietary groups (commercial, okra-spirulina, and spirulina) were studied, focusing on embryonic development, oxidative damage, and gene expression changes. The study revealed that diets enriched with spirulina and okra-spirulina effectively reduced aluminum-induced embryotoxicity, oxidative stress, and gene expression alterations, surpassing the commercial diet. However, all AlCl3-exposed groups experienced adverse effects on embryonic development, including hatching anomalies, structural deformities, and cardiac delays. The okra-spirulina group showed milder toxic responses. In conclusion, this study highlights the potential of spirulina and okra-spirulina diets in mitigating aluminum-triggered oxidative stress and apoptosis in D. rerio. It underscores the need for future research on embryonic development and carries significant implications for environmental conservation and the well-being of aquatic organisms in aluminum-contaminated environments.

Overview of microalgae and cyanobacteria-based biostimulants produced from wastewater and CO2 streams towards sustainable agriculture: A review

For a long time, marine macroalgae (seaweeds) have been used to produce commercial biostimulants in order to ensure both productivity and quality of agricultural crops under abiotic stress. With similar biological properties, microalgae have slowly attracted the scientific community and the biostimulant industry, in particular because of their ability to be cultivated on non-arable lands with high biomass productivity all year long. Moreover, the recent strategies of culturing these photosynthetic microorganisms using wastewater and CO2 opens the possibility to produce large quantity of biomass at moderate costs while integrating local and circular economy approaches. This paper aims to provide a state of the art review on the development of microalgae and cyanobacteria based biostimulants, focusing on the different cultivation, extraction and application techniques available in the literature. Emphasis will be placed on microalgae and cyanobacteria cultivation using liquid and gaseous effluents as well as emerging green-extraction approaches, taking in consideration the actual European regulatory framework.

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.

Chlamydomonas reinhardtii-A Reference Microorganism for Eukaryotic Molybdenum Metabolism

Molybdenum (Mo) is vital for the activity of a small but essential group of enzymes called molybdoenzymes. So far, specifically five molybdoenzymes have been discovered in eukaryotes: nitrate reductase, sulfite oxidase, xanthine dehydrogenase, aldehyde oxidase, and mARC. In order to become biologically active, Mo must be chelated to a pterin, forming the so-called Mo cofactor (Moco). Deficiency or mutation in any of the genes involved in Moco biosynthesis results in the simultaneous loss of activity of all molybdoenzymes, fully or partially preventing the normal development of the affected organism. To prevent this, the different mechanisms involved in Mo homeostasis must be finely regulated. Chlamydomonas reinhardtii is a unicellular, photosynthetic, eukaryotic microalga that has produced fundamental advances in key steps of Mo homeostasis over the last 30 years, which have been extrapolated to higher organisms, both plants and animals. These advances include the identification of the first two molybdate transporters in eukaryotes (MOT1 and MOT2), the characterization of key genes in Moco biosynthesis, the identification of the first enzyme that protects and transfers Moco (MCP1), the first characterization of mARC in plants, and the discovery of the crucial role of the nitrate reductase-mARC complex in plant nitric oxide production. This review aims to provide a comprehensive summary of the progress achieved in using C. reinhardtii as a model organism in Mo homeostasis and to propose how this microalga can continue improving with the advancements in this field in the future.