Biopolymers for Biological Control of Plant Pathogens: Advances in Microencapsulation of Beneficial Microorganisms

Encapsulation of Active Substances in Natural Polymer Coatings

Already used in the food, pharmaceutical, cosmetic, and agrochemical industries, encapsulation is a strategy used to protect active ingredients from external degradation factors and to control their release kinetics. Various encapsulation techniques have been studied, both to optimise the level of protection with respect to the nature of the aggressor and to favour a release mechanism between diffusion of the active compounds and degradation of the barrier material. Biopolymers are of particular interest as wall materials because of their biocompatibility, biodegradability, and non-toxicity. By forming a stable hydrogel around the drug, they provide a 'smart' barrier whose behaviour can change in response to environmental conditions. After a comprehensive description of the concept of encapsulation and the main technologies used to achieve encapsulation, including micro- and nano-gels, the mechanisms of controlled release of active compounds are presented. A panorama of natural polymers as wall materials is then presented, highlighting the main results associated with each polymer and attempting to identify the most cost-effective and suitable methods in terms of the encapsulated drug.

Innovative Encapsulation Strategies for Food, Industrial, and Pharmaceutical Applications

Bioactive metabolites obtained from fruits and vegetables as well as many drugs have various capacities to prevent or treat various ailments. Nevertheless, their efficiency, in vivo, encounter many challenges resulting in lower efficacy as well as different side effects when high doses are used resulting in many challenges for their application. Indeed, demand for effective treatments with no or less unfavorable side effects is rising. Delivering active molecules to a particular site of action within the human body is an example of targeted therapy which remains a challenging field. Developments of nanotechnology and polymer science have great promise for meeting the growing demands of efficient options. Encapsulation of active ingredients in nano-delivery systems has become as a vitally tool for protecting the integrity of critical biochemicals, improving their delivery, enabling their controlled release and maintaining their biological features. Here, we examine a wide range of nano-delivery techniques, such as niosomes, polymeric/solid lipid nanoparticles, nanostructured lipid carriers, and nano-emulsions. The advantages of encapsulation in targeted, synergistic, and supportive therapies are emphasized, along with current progress in its application. Additionally, a revised collection of studies was given, focusing on improving the effectiveness of anticancer medications and addressing the problem of antimicrobial resistance. To sum up, this paper conducted a thorough analysis to determine the efficacy of encapsulation technology in the field of drug discovery and development.

Nature's coatings: Sodium alginate as a novel coating in safeguarding plants from frost damages

Frost damage remains a significant challenge for agricultural practices worldwide, leading to substantial economic losses and food insecurity. Practically, traditional methods for frost management have proven ineffective and come with several drawbacks, such as energy consumption and limited efficacy. Hence, proposing an anti-freezing coating can be an innovative idea. The potential of sodium alginate (SA) to construct anti-freezing hydrogels has been explored in several sciences. SA hydrogels can form protective films around plants as a barrier against freezing temperatures and ice crystals on the plant's surface. Sodium alginate exhibits excellent water retention, enhancing plant hydration during freezing conditions. This coating can provide insulation, effectively shielding the plant from frost damage. The advantages of SA as a coating material, such as its biocompatibility, biodegradability, and non-toxic nature, are highlighted. Therefore, the proposed use of SA as an innovative coating material holds promise for safeguarding plants from frost damage. Following SA potential and frost's huge damage, the present review provides a comprehensive overview of the recent developments in SA-based anti-freezing hydrogels, their applications, and their potential in agriculture as anti-freezing coatings. However, further research and field trials are necessary to optimize the application methods and understand the long-term effects on productivity.

Nano/Micro-Structural Supramolecular Biopolymers: Innovative Networks with the Boundless Potential in Sustainable Agriculture

Sustainable agriculture plays a crucial role in meeting the growing global demand for food while minimizing adverse environmental impacts from the overuse of synthetic pesticides and conventional fertilizers. In this context, renewable biopolymers being more sustainable offer a viable solution to improve agricultural sustainability and production. Nano/micro-structural supramolecular biopolymers are among these innovative biopolymers that are much sought after for their unique features. These biomaterials have complex hierarchical structures, great stability, adjustable mechanical strength, stimuli-responsiveness, and self-healing attributes. Functional molecules may be added to their flexible structure, for enabling novel agricultural uses. This overview scrutinizes how nano/micro-structural supramolecular biopolymers may radically alter farming practices and solve lingering problems in agricultural sector namely improve agricultural production, soil health, and resource efficiency. Controlled bioactive ingredient released from biopolymers allows the tailored administration of agrochemicals, bioactive agents, and biostimulators as they enhance nutrient absorption, moisture retention, and root growth. Nano/micro-structural supramolecular biopolymers may protect crops by appending antimicrobials and biosensing entities while their eco-friendliness supports sustainable agriculture. Despite their potential, further studies are warranted to understand and optimize their usage in agricultural domain. This effort seeks to bridge the knowledge gap by investigating their applications, challenges, and future prospects in the agricultural sector. Through experimental investigations and theoretical modeling, this overview aims to provide valuable insights into the practical implementation and optimization of supramolecular biopolymers in sustainable agriculture, ultimately contributing to the development of innovative and eco-friendly solutions to enhance agricultural productivity while minimizing environmental impact.

A review of chitosan nanoparticles: Nature's gift for transforming agriculture through smart and effective delivery mechanisms

Chitosan nanoparticles (CNPs) have emerged as a promising tool in agricultural advancements due to their unique properties including, biocompatability, biodegradability, non-toxicity and remarkable versatility. These inherent properties along with their antimicrobial, antioxidant and eliciting activities enable CNPs to play an important role in increasing agricultural productivity, enhancing nutrient absorption and improving pest management strategies. Furthermore, the nano-formulation of chitosan have the ability to encapsulate various agricultural amendments, enabling the controlled release of pesticides, fertilizers, plant growth promoters and biocontrol agents, thus offering precise and targeted delivery mechanisms for enhanced efficiency. This review provides a comprehensive analysis of the latest research and developments in the use of CNPs for enhancing agricultural practices through smart and effective delivery mechanisms. It discusses the synthesis methods, physicochemical properties, and their role in enhancing seed germination and plant growth, crop protection against biotic and abiotic stresses, improving soil quality and reducing the environmental pollution and delivery of agricultural amendments. Furthermore, the potential environmental benefits and future directions for integrating CNPs into sustainable agricultural systems are explored. This review aims to shed light on the transformative potential of chitosan nanoparticles as nature's gift for revolutionizing agriculture and fostering eco-friendly farming practices.

Advancements in coating technologies: Unveiling the potential of chitosan for the preservation of fruits and vegetables

Post-harvest losses of fruits and vegetables pose a significant challenge to the agriculture industry worldwide. To address this issue, researchers have turned to natural and eco-friendly solutions such as chitosan coatings. Chitosan, a biopolymer derived from chitin, has gained considerable attention due to its unique properties such as non-toxicity, biodegradability, biocompatibility and potential applications in post-harvest preservation. This review article provides an in-depth analysis of the current state of research on chitosan coatings for the preservation of fruits and vegetables. Moreover, it highlights the advantages of using chitosan coatings, including its antimicrobial, antifungal, and antioxidant properties, as well as its ability to enhance shelf-life and maintain the quality attributes of fresh product. Furthermore, the review discusses the mechanisms by which chitosan interacts with fruits and vegetables, elucidating its antimicrobial activity, modified gas permeability, enhanced physical barrier and induction of host defense responses. It also examines the factors influencing the effectiveness of chitosan coatings, such as concentration, molecular weight, deacetylation degree, pH, temperature, and application methods.

Advancing agriculture through bioresource technology: The role of cellulose-based biodegradable mulches

Agriculture plays a pivotal role in meeting the world's ever-growing food demands. However, traditional agricultural practices often have negative consequences for the environment, such as soil erosion and chemical runoff. Recently, there has been a pressing need for advance agricultural practices. Cellulose-based mulches offer a solution by optimizing agricultural productivity while minimizing harm. These mulches are made from renewable bioresources derived from cellulose-rich materials. Compared to plastic mulches, cellulose-based alternatives show potential in improving nutrient retention, soil health, weed suppression, water conservation, and erosion mitigation. The article investigates the characteristics and application methods of cellulose-based mulches, highlighting their biodegradability, water retention, crop protection, and weed suppression capabilities. It also evaluates their economic feasibility, emphasizing their potential to transform sustainable farming practices. Overall, cellulose-based mulches have the potential to revolutionize agriculture, addressing environmental concerns while optimizing productivity. They represent a significant step toward a more sustainable and resilient agricultural system.

A Simple Allelic Exchange Method for Efficient Seamless Knockout of Up to 34-kbp-Long Gene Cassettes in Pseudomonas

Gene knockout is a widely used technique for engineering bacterial genomes, investigating the roles of genes in metabolism, and conferring biological characteristics. Herein, we developed a rapid, efficient, and simple method for the knockout of long gene cassettes in Pseudomonas spp., based on a traditional allelic exchange strategy. The upstream and downstream sequences of the target gene cluster to be deleted were amplified using primers with 5'-end sequences identical to the multiple cloning sites of a suicide plasmid (mutant allele insert vector). The sequences were then fused with the linearized suicide plasmid in one step via seamless cloning. The resulting allelic exchange vector (recombinant plasmid) was introduced from the donor strain (Escherichia coli SM 10) into recipient cells (Pseudomonas putida, P. composti, and P. khazarica) via conjugation. Single-crossover merodiploids (integrates the vector into host chromosome by homologous recombination) were screened based on antibiotic resistance conferred by the plasmid, and double-crossover haploids (deleting the target gene clusters and inserted alien plasmid backbone) were selected using sucrose-mediated counterselection. Unlike other approaches, the method described herein introduces no selective marker genes into the genomes of the knockout mutants. Using our method, we successfully deleted polysaccharide-encoding gene clusters in P. putida, P. composti, and P. khazarica and generated four mutants with single-gene cassette deletions up to 18 kbp and one mutant with double-gene cassette deletion of approximately 34 kbp. Collectively, our results indicate that this method is ideal for the deletion of long genetic sequences, yielding seamless mutants of various Pseudomonas spp.

Can we control potato fungal and bacterial diseases? - microbial regulation

The potato plant is one of the main crops in the world. However, relatively little is known about key virulence factors of major fungal and bacterial diseases in potatoes, biocontrol measures to improve activity and stability, and the core driving forces in the control process. Here, we focus on analyzing the mechanisms by which genes, proteins, or (and) metabolites of potato pathogens as key virulence factors. Then, the single strain biocontrol agents, synthetic microbial communities, microbial microcapsule strategies were introduced, and the latter two strategies can improve stability and activity in biocontrol. Meanwhile, summarized the defense mechanisms of biocontrol and their specific issues in practical applications. Furthermore, explore how potato crop management, soil management, and climate effects, as crucial driving forces affect potato biocontrol in the system. Dynamic and systematic research, excavation of biocontrol strain resources, find the causes of regional disease resistance and exploration of biocontrol mechanism will provide promising solutions for biotic stress faced by potato in the future.

Characterization and biocontrol mechanism of Streptomyces olivoreticuli as a potential biocontrol agent against Rhizoctonia solani

Rhizoctonia solani is a widespread and devastating plant pathogenic fungus that infects many important crops. This pathogen causes tobacco target spot, a disease that is widespread in many tobacco-growing countries and is destructive to tobacco. To identify antagonistic microorganisms with biocontrol potential against this disease, we isolated Streptomyces strains from forest inter-root soil and screened a promising biocontrol strain, ZZ-21. Based on in vitro antagonism assays, ZZ-21 showed a significant inhibitory effect on R. solani and various other phytopathogens. ZZ-21 was identified as Streptomyces olivoreticuli by its phenotypic, genetic, physiological and biochemical properties. Complete genome sequencing revealed that ZZ-21 harbored numerous antimicrobial biosynthesis gene clusters. ZZ-21 significantly reduced the lesion length in detached inoculated leaf assays and reduced the disease index under greenhouse and field conditions. Based on an in vitro antagonistic assay of ZZ-21 culture, the strain exhibited an antifungal activity against R. solani in a dose-dependent manner. The culture filtrate could impair membrane integrity, possibly through membrane lipid peroxidation. ZZ-21 could secrete multiple extracellular enzymes and siderophores. According to a series of antifungal assays, the extracellular metabolites of ZZ-21 contained antimicrobial bioactive compounds composed of proteins/peptides extracted using ammonium sulfate precipitation, which were stable under stress caused by high temperature and protease K. The EC50 value for ammonium sulfate precipitation was determined to be 21.11 μg/mL in this study. Moreover, the proteins/peptides also exhibited biocontrol ability and were observed to alter the plasma membrane integrity of R. solani which were evaluated by biocontrol efficacy assays on detached tobacco leaves and PI staining. Overall, strain ZZ-21 shows the potential to be developed into a biopesticide against tobacco target spot disease.

Chitosan-Delivered Chlorantraniliprole for Pest Control: Preparation Optimization, Deposition Behavior, and Application Potential

Chitosan has emerged as a promising biopolymer carrier for the sustained release of pesticides owing to its good biocompatibility, biodegradability, and bioactivity. In this work, a controlled-release formulation of insecticide chlorantraniliprole was fabricated through coprecipitation-based synchronous encapsulation with chitosan, where the optimum preparation conditions, storage stability, deposition behavior, and application potential were investigated. Preparation of optimization data from response surface methodology showed high correlation coefficient (R2) of 0.9875 and adjusted coefficient (Radj2) of 0.9715. The resulting formulation displayed good loading content of 28.39%, high encapsulation efficiency of 75.71%, and good storage stability. Compared with the commercial suspension concentrate, the formulation exhibited better wettability and retention behaviors on plant leaves. Excitingly, effective control against one species of mealybug genus Paraputo Laing (outside the killing spectrum) on the Hippeastrum reticulatum plant was successfully achieved by spraying the controlled-release formulation at different time intervals. This work indicates the good potential of the developed formulation in expanding the application scope of chlorantraniliprole, which shows a new strategy for sustainable pest management.

Application of polysaccharides for the encapsulation of beneficial microorganisms for agricultural purposes: A review

Intensive farming practices have increased the consumption of chemical-based pesticides and fertilizers thereby creating health issues for humans and animals and also causing a deterioration in the natural ecosystem. The promotion of biomaterials synthesis could potentially lead to the replacement of synthetic products and improve soil fertility, protect plants from pathogen attacks, and enhance the productivity of the agricultural sector resulting in less environmental pollution. Microbial bioengineering involving the use and improvement of encapsulation using polysaccharides has the required potential to address environmental issues and promote green chemistry. This article describes various encapsulation techniques and polysaccharides which have an immense applicable capability to encapsulate microbial cells. The review elucidates the factors that may result in a reduced viable cell count during encapsulation, particularly using the spray drying method, where a high temperature is required to dry the suspension, this may damage the microbial cells. The environmental advantage of the application of polysaccharides as carriers of beneficial microorganisms, which do not pose a risk for soil due to their full biodegradability, was also shown. The encapsulated microbial cells may assist in addressing certain environmental problems such as ameliorating the unfavourable effects of plant pests and pathogens, and promoting agricultural sustainability.

Chitosan-based nanocomposites as coatings and packaging materials for the postharvest improvement of agricultural product: A review

The perishability nature of harvested fruits and vegetables, along with the effect of environmental factors, storage conditions, and transportation, reduce the products' quality and shelf-life. Considerable efforts have been allocated to alternate conventional coatings based on new edible biopolymers for packaging. Chitosan is an attractive alternative to synthetic plastic polymers due to its biodegradability, antimicrobial activity, and film-forming properties. However, its conservative properties can be improved by adding active compounds, limiting microbial agents' growth and biochemical and physical damages, and enhancing the stored products' quality, shelf-life, and consumer acceptability. Most of the research on chitosan-based coatings focuses on antimicrobial or antioxidant properties. Along with the advancement of polymer science and nanotechnology, novel chitosan blends with multiple functionalities are required and should be fabricated using numerous strategies, especially for application during storage. This review discusses recent developments in using chitosan as a matrix to fabricate bioactive edible coatings and their positive impacts on increasing the quality and shelf-life of fruits and vegetables.

Encapsulated plant growth regulators and associative microorganisms: Nature-based solutions to mitigate the effects of climate change on plants

Over the past decades, the atmospheric CO₂ concentration and global average temperature have been increasing, and this trend is projected to soon become more severe. This scenario of climate change intensifies abiotic stress factors (such as drought, flooding, salinity, and ultraviolet radiation) that threaten forest and associated ecosystems as well as crop production. These factors can negatively affect plant growth and development with a consequent reduction in plant biomass accumulation and yield, in addition to increasing plant susceptibility to biotic stresses. Recently, biostimulants have become a hotspot as an effective and sustainable alternative to alleviate the negative effects of stresses on plants. However, the majority of biostimulants have poor stability under environmental conditions, which leads to premature degradation, shortening their biological activity. To solve these bottlenecks, micro- and nano-based formulations containing biostimulant molecules and/or microorganisms are gaining attention, as they demonstrate several advantages over their conventional formulations. In this review, we focus on the encapsulation of plant growth regulators and plant associative microorganisms as a strategy to boost their application for plant protection against abiotic stresses. We also address the potential limitations and challenges faced for the implementation of this technology, as well as possibilities regarding future research.

Exploring the roles of starch for microbial encapsulation through a systematic mapping review

Microorganism encapsulation protects them from stressful conditions and assists in maintaining their viability, being especially beneficial when the carrier material is a renewable and biodegradable biopolymer, such as starch. Here, a systematic mapping was performed to provide a current overview on the use of starch-based systems for microbial encapsulation. Following well-established guidelines, a systematic mapping was conducted and the following could be drawn: 1) there was a significant increase in publications on microbial encapsulation using starch over the past decade, showing interest from the scientific community, 2) ionotropic gelation, emulsification and spray drying are the most commonly used techniques for starch-based microbial encapsulation, and 3) starch play important functions in the encapsulation matrix such as assisting in the survival of the microorganisms. The information gathered in this systematic mapping can be useful to guide researchers and industrial sectors on the development of innovative starch-based systems for microbial encapsulation.

Use of whey protein as a natural polymer for the encapsulation of plant biocontrol bacteria: A review

Climate changes, drought, the salinity of water and soil, the emergence of new breeds of pests and pathogens, the industrialization of countries, and environmental contamination are among the factors limiting the production of agricultural products. The use of chemicals (in the form of fertilizers, pesticides and fungicides) to enhance products against biotic and abiotic stresses has limitations. To eliminate the effects of agricultural chemicals, synthetic agrochemicals should be replaced with natural substances and useful microorganisms. To be more effective and efficient, plant biocontrol bacteria need a coating layer around themselves to protect them from adverse conditions. Whey protein, a valuable by-product of the cheese industry, is one of the important natural polymers. Due to its high protein content, safety, and biodegradability, whey can have many applications in agriculture and encapsulation of bacteria to resist pests and plant diseases. This compound is a rich source of amino acids that can activate plant defense systems and defense enzymes. Considering the amazing potentialities of formulation whey protein, this review attends to the efficiency of whey protein as coating layers on fruit and vegetables and in the packaging system to increase the shelf life of agricultural products against phytopathogens.

Chitosan/silica: A hybrid formulation to mitigate phytopathogens

Long-term and indiscriminate use of synthetic pesticides to mitigate plant pathogens have created serious issues of water health, soil contamination, non-target organisms, resistant species, and unpredictable environmental and human health hazards. These constraints have forced scientists to develop alternative plant disease management strategies to reduce synthetic chemical' dependency. During the last 20 years, biological agents and resistance elicitors have been the most important used alternatives. Silica-based materials/chitosan with a dual mode of action have been proposed as promising alternatives to prevent plant diseases through direct and indirect mechanisms. Moreover, the combined application of nano-silica and chitosan, due to their controllable morphology, high loading capacity, low toxicity, and efficient encapsulation, act as suitable carriers for biological agents, pesticides, and essential oils, making them proper candidates for mitigation of phytopathogens. Based on this potential, this literature study reviewed the silica and chitosan properties and their function in the plant. It also assessed their role in the fighting against soil and aerial phytopathogens, directly and indirectly, as novel hybrid formulations in future managing platforms.

Micro-/Nano-Carboxymethyl Cellulose as a Promising Biopolymer with Prospects in the Agriculture Sector: A Review

The increase in the population rate has increased the demand for safe and quality food products. However, the current agricultural system faces many challenges in producing vegetables and fruits. Indiscriminate use of pesticides and fertilizers, deficiency of water resources, short shelf life of products postharvest, and nontargeted delivery of agrochemicals are the main challenges. In this regard, carboxymethyl cellulose (CMC) is one of the most promising materials in the agriculture sector for minimizing these challenges due to its mechanical strength, viscosity, wide availability, and edibility properties. CMC also has high water absorbency; therefore, it can be used for water deficiency (as superabsorbent hydrogels). Due to the many hydroxyl groups on its surface, this substance has high efficacy in removing pollutants, such as pesticides and heavy metals. Enriching CMC coatings with additional substances, such as antimicrobial, antibrowning, antioxidant, and antisoftening materials, can provide further novel formulations with unique advantages. In addition, the encapsulation of bioactive materials or pesticides provides a targeted delivery system. This review presents a comprehensive overview of the use of CMC in agriculture and its applications for preserving fruit and vegetable quality, remediating agricultural pollution, preserving water sources, and encapsulating bioactive molecules for targeted delivery.

Chitin and its derivatives: Functional biopolymers for developing bioproducts for sustainable agriculture-A reality?

Chitinous materials (chitin and its derivatives) are obtained from renewable sources, mainly shellfish waste, having a great potential for the development of bioproducts as alternatives to synthetic agrochemicals. Recent studies have provided evidence that the use of these biopolymers can help control postharvest diseases, increase the content of nutrients available to plants, and elicit positive metabolic changes that lead to higher plant resistance against pathogens. However, agrochemicals are still widely and intensively used in agriculture. This perspective addresses the gap in knowledge and innovation to make bioproducts based on chitinous materials more competitive in the market. It also provides the readers with background to understand why these products are scarcely used and the aspects that need to be considered to increase their use. Finally, information on the development and commercialization of agricultural bioproducts containing chitin or its derivatives in the Chilean market is also provided.

Performance appraisal of Trichoderma viride based novel tablet and powder formulations for management of Fusarium wilt disease in chickpea

In developing a Trichoderma viride-based biocontrol program for Fusarium wilt disease in chickpea, the choice of the quality formulation is imperative. In the present study, two types of formulations i.e. powder for seed treatment (TvP) and tablet for direct application (TvT), employing T. viride as the biocontrol agent, were evaluated for their ability to control chickpea wilt under field conditions at three dosages i.e. recommended (RD), double of recommended (DD) and half of recommended (1/2 RD). A screening study for the antagonistic fungi strains based on volatile and non-volatile bioassays revealed that T. viride ITCC 7764 has the most potential among the five strains tested (ITCC 6889, ITCC 7204, ITCC 7764, ITCC 7847, ITCC 8276), which was then used to develop the TvP and TvT formulations. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of volatile organic compounds (VOCs) of T. viride strain confirmed the highest abundance of compositions comprising octan-3-one (13.92%), 3-octanol (10.57%), and 1-octen-3-ol (9.40%) in the most potential T. viride 7764. Further Physico-chemical characterization by standard Collaborative International Pesticides Analytical Council (CIPAC) methods revealed the optimized TvP formulation to be free flowing at pH 6.50, with a density of 0.732 g cm^-3. The TvT formulation showed a pH value of 7.16 and density of 0.0017 g cm^-3 for a complete disintegration time of 22.5 min. The biocontrol potential of TvP formulation was found to be superior to that of TvT formulation in terms of both seed germination and wilt incidence in chickpea under field conditions. However, both the developed formulations (TvP and TvT) expressed greater bioefficacy compared to the synthetic fungicide (Carbendazim 50% WP) and the conventional talc-based formulation. Further research should be carried out on the compatibility of the developed products with other agrochemicals of synthetic or natural origin to develop an integrated disease management (IDM) schedule in chickpea.

Novel Approaches for Encapsulation of Plant Probiotic Bacteria with Sustainable Polymer Gums: Application in the Management of Pests and Diseases

The unique attributes, biodegradability, biocompatibility, perfect accessibility, and low production costs led to the use of natural gums in a different section of our lives. Among them, we can mention gums obtained from microorganisms (xanthan gum and gellan gum), plant tissues (Arabic gum and gum tragacanth), seeds (konjac gum and guar gum), seaweeds (alginates, agar gum, and carrageenans). Gums have essential applications in the medical and pharmaceutical, food, biotechnology, and critical agricultural industries. Encapsulation is one of the new methods to increase the stability of bioactive compounds during processing and storage. Encapsulation technology using natural gums is a new way to improve the performance of microbial agents in various sciences, especially agriculture, which represents a bright future in this field.

Review and Perspectives of the Use of Alginate as a Polymer Matrix for Microorganisms Applied in Agro-Industry

Alginate is a polysaccharide with the property of forming hydrogels, which is economic production, zero toxicity, and biocompatibility. In the agro-industry, alginate is used as a super absorbent polymer, coating seeds, fruits, and vegetables and as a carrier of bacteria and fungi as plant-growth promoters and biocontrol. The latter has a high impact on agriculture since the implementation of microorganisms in a polymer matrix improves soil quality; plant nutrition, and is functional as a preventive measure for the appearance of phytopathogenic. Additionally, it minimizes losses of foods due to wrong post-harvest handling. In this review, we provide an overview of physicochemical properties of alginate, some methods for preparation and modification of capsules and coatings, to finally describe its application in agro-industry as a matrix of plant-growth-promoting microorganisms, its effectiveness in cultivation and post-harvest, and its effect on the environment, as well as the prospects for future agro-industrial applications.

Microencapsulation of Essential Oils: A Review

Essential oils (EOs) are complex mixtures of volatile compounds extracted from different parts of plants by different methods. There is a large diversity of these natural substances with varying properties that lead to their common use in several areas. The agrochemical, pharmaceutical, medical, food, and textile industry, as well as cosmetic and hygiene applications are some of the areas where EOs are widely included. To overcome the limitation of EOs being highly volatile and reactive, microencapsulation has become one of the preferred methods to retain and control these compounds. This review explores the techniques for extracting essential oils from aromatic plant matter. Microencapsulation strategies and the available technologies are also reviewed, along with an in-depth overview of the current research and application of microencapsulated EOs.

Encapsulation of Azotobacter vinelandii ATCC 12837 in Alginate-Na Beads as a Tomato Seedling Inoculant

Encapsulation is an immobilization method characterized by restricting microbial cells to a delimited area while preserving their metabolic viability. This technique represents an alternative to improve the adaptive capacity of bacteria in the face of interactions with native microorganisms and environmental factors that limit their inoculation. This study aimed to evaluate the effect of Azotobacter vinelandii ATCC 12837 encapsulated in alginate-Na beads as an inoculant of tomato (Solanum Lycopersicum L) seedlings. Two inoculation treatments were carried out: liquid and encapsulated, and the control without microorganisms. Physiological variables, microbial viability, and the presence of A. vinelandii were determined by qPCR. Inoculation with A. vinelandii in liquid and encapsulated form favored seedling growth. Plants with the encapsulated inoculum significantly increased germination percentage (20%), stem diameter (38%), seedling height (34%), root length (69%), NO₃ concentration (41%), and Na (30%); compared to the control. Encapsulation of A. vinelandii in alginate-Na macrocapsules allowed its establishment in the rhizosphere and was corroborated by viable count and molecular methods. The viability of the bacteria was maintained for 28 days using both inoculation methods, and not detected in the control treatment.

Salinity Stress: Toward Sustainable Plant Strategies and Using Plant Growth-Promoting Rhizobacteria Encapsulation for Reducing It

Salinity is one of the most important abiotic stresses that influences plant growth and productivity worldwide. Salinity affects plant growth by ionic toxicity, osmotic stress, hormonal imbalance, nutrient mobilization reduction, and reactive oxygen species (ROS). To survive in saline soils, plants have developed various physiological and biochemical strategies such as ion exchange, activation of antioxidant enzymes, and hormonal stimulation. In addition to plant adaption mechanisms, plant growth-promoting rhizobacteria (PGPR) can enhance salt tolerance in plants via ion homeostasis, production of antioxidants, ACC deaminase, phytohormones, extracellular polymeric substance (EPS), volatile organic compounds, accumulation of osmolytes, activation of plant antioxidative enzymes, and improvement of nutrients uptake. One of the important issues in microbial biotechnology is establishing a link between the beneficial strains screened in the laboratory with industry and the consumer. Therefore, in the development of biocontrol agents, it is necessary to study the optimization of conditions for mass reproduction and the selection of a suitable carrier for their final formulation. Toward sustainable agriculture, the use of appropriate formulations of bacterial agents as high-performance biofertilizers, including microbial biocapsules, is necessary to improve salt tolerance and crop productivity.

Encapsulation of Plant Biocontrol Bacteria with Alginate as a Main Polymer Material

One of the most favored trends in modern agriculture is biological control. However, many reports show that survival of biocontrol bacteria is poor in host plants. Providing biocontrol agents with protection by encapsulation within external coatings has therefore become a popular idea. Various techniques, including extrusion, spray drying, and emulsion, have been introduced for encapsulation of biocontrol bacteria. One commonly used biopolymer for this type of microencapsulation is alginate, a biopolymer extracted from seaweed. Recent progress has resulted in the production of alginate-based microcapsules that meet key bacterial encapsulation requirements, including biocompatibility, biodegradability, and support of long-term survival and function. However, more studies are needed regarding the effect of encapsulation on protective bacteria and their targeted release in organic crop production systems. Most importantly, the efficacy of alginate use for the encapsulation of biocontrol bacteria in pest and disease management requires further verification. Achieving a new formulation based on biodegradable polymers can have significant effects on increasing the quantity and quality of agricultural products.

Application of Streptomyces Antimicrobial Compounds for the Control of Phytopathogens

One of the relevant problems in today's agriculture is related to phytopathogenic microorganisms that cause between 30–40% of crop losses. Synthetic chemical pesticides and antibiotics have brought human and environmental health problems and microbial resistance to these treatments. So, the search for natural alternatives is necessary. The genus Streptomyces have broad biotechnological potential, being a promising candidate for the biocontrol of phytopathogenic microorganisms. The efficacy of some species of this genus in plant protection and their continued presence in the intensely competitive rhizosphere is due to its great potential to produce a wide variety of soluble bioactive secondary metabolites and volatile organic compounds. However, more attention is still needed to develop novel formulations that could increase the shelf life of streptomycetes, ensuring their efficacy as a microbial pesticide. In this sense, encapsulation offers an advantageous and environmentally friendly option. The present review aims to describe some phytopathogenic microorganisms with economic importance that require biological control. In addition, it focuses mainly on the Streptomyces genus as a great producer of secondary metabolites that act on other microorganisms and plants, exercising its role as biological control. The review also covers some strategies and products based on Streptomyces and the problems of its application in the field.