Bacterial alginate production: an overview of its biosynthesis and potential industrial production

Enhanced wound healing properties of biodegradable PCL/alginate core-shell nanofibers containing Salvia abrotanoides essential oil and ZnO nanoparticles

Electrospun nanofibrous membranes, with their unique structural features, can potentially enhance wound healing through controlled delivery of active agents. Here, an innovative porous nanofibrous membrane was developed as a dressing patch with antibacterial and anti-inflammatory functionalities for cutaneous wound healing. Zinc oxide nanoparticles (ZnO NPs) and Salvia abrotanoides essential oil (SAEO) were incorporated into sodium alginate, which served as the shell. Poly(ε-caprolactone) was used as the core of coaxial electrospun wound dressing nanofibers (PCL/SA@ZnO/SAEO). With the addition of ZnO NPs and SAEO, the average diameter of nanofibers was 187 ± 51 nm, with improved tensile strength (4.7 ± 0.4 MPa), elongation at break (32.9 ± 2.1), and elastic modulus (21.4 ± 2.0). Concurrent application of ZnO NPs and SAEO increased antimicrobial activity against Staphylococcus aureus and Escherichia coli and promoted the proliferation, attachment, and viability (>90 %) of L929 cells. The PCL/SA@ZnO/SAEO scaffold accelerated the healing time with total wound healing over 14 days in mouse models carrying full-thickness wounds compared to the nanofibrous scaffold without additives. Histopathological examinations demonstrated better tissue regeneration, i.e., enhanced collagen deposition, improved re-epithelialization, and neovascularization, and increased quantity of hair follicles. Moreover, the chicken chorioallantoic membrane assay confirmed the synergistic angiogenic effects of SAEO and ZnO NPs. Finally, the in vitro and in vivo results proposed the bioactive core-shell nanofibers synthesized as encouraging wound dressing materials for hastening the healing of cutaneous wounds.

A Homolog of the Histidine Kinase RetS Controls the Synthesis of Alginates, PHB, Alkylresorcinols, and Motility in Azotobacter vinelandii

The two-component system GacS/A and the posttranscriptional control system Rsm constitute a genetic regulation pathway in Gammaproteobacteria; in some species of Pseudomonas, this pathway is part of a multikinase network (MKN) that regulates the activity of the Rsm system. In this network, the activity of GacS is controlled by other kinases. One of the most studied MKNs is the MKN-GacS of Pseudomonas aeruginosa, where GacS is controlled by the kinases RetS and LadS; RetS decreases the kinase activity of GacS, whereas LadS stimulates the activity of the central kinase GacS. Outside of the Pseudomonas genus, the network has been studied only in Azotobacter vinelandii. In this work, we report the study of the RetS kinase of A. vinelandii; as expected, the phenotypes affected in gacS mutants, such as production of alginates, polyhydroxybutyrate, and alkylresorcinols and swimming motility, were also affected in retS mutants. Interestingly, our data indicated that RetS in A. vinelandii acts as a positive regulator of GacA activity. Consistent with this finding, mutation in retS also negatively affected the expression of small regulatory RNAs belonging to the Rsm family. We also confirmed the interaction of RetS with GacS, as well as with the phosphotransfer protein HptB.

Structural basis for the minimal bifunctional alginate epimerase AlgE3 from Azotobacter chroococcum

Among the epimerases specific to alginate, some of them in Azotobacter genera convert β-d-mannuronic acid to α-l-guluronic acid but also have lyase activity to degrade alginate. The remarkable characteristics of these epimerases make it a promising enzyme for tailoring alginates to meet specific demands. Here, we determined the structure of the bifunctional mannuronan C-5 epimerase AlgE3 from Azotobacter chroococcum (AcAlgE3) in complex with several mannuronic acid oligomers as well as in apo form, which allowed us to elucidate the binding manner of each mannuronic acid oligomer, and the structural plasticity, which is dependent on calcium ions. Moreover, a comprehensive analysis of the lyase activity profiles of AcAlgE3 combined with structural characteristics explained the preference for different chain length oligomers.

Advances in alginate lyases and the potential application of enzymatic prepared alginate oligosaccharides: A mini review

Alginate is mainly a linear polysaccharide composed of randomly arranged β-D-mannuronic acid and α-L-guluronic acid linked by α, β-(1,4)-glycosidic bonds. Alginate lyases degrade alginate mainly adopting a β-elimination mechanism, breaking the glycosidic bonds between the monomers and forming a double bond between the C4 and C5 sugar rings to produce alginate oligosaccharides consisting of 2-25 monomers, which have various physiological functions. Thus, it can be used for the continuous industrial production of alginate oligosaccharides with a specific degree of polymerization, in accordance with the requirements of green exploitation of marine resources. With the development of structural analysis, the quantity of characterized alginate lyase structures is progressively growing, leading to a concomitant improvement in understanding the catalytic mechanism. Additionally, the use of molecular modification methods including rational design, truncated expression of non-catalytic domains, and recombination of conserved domains can improve the catalytic properties of the original enzyme, enabling researchers to screen out the enzyme with the expected excellent performance with high success rate and less workload. This review presents the latest findings on the catalytic mechanism of alginate lyases and outlines the methods for molecular modifications. Moreover, it explores the connection between the degree of polymerization and the physiological functions of alginate oligosaccharides, providing a reference for enzymatic preparation development and utilization.

Bacteria for Bioplastics: Progress, Applications, and Challenges

Bioplastics are one of the answers that can point society toward a sustainable future. Under this premise, the synthesis of polymers with competitive properties using low-cost starting materials is a highly desired factor in the industry. Also, tackling environmental issues such as nonbiodegradable waste generation, high carbon footprint, and consumption of nonrenewable resources are some of the current concerns worldwide. The scientific community has been placing efforts into the biosynthesis of polymers using bacteria and other microbes. These microorganisms can be convenient reactors to consume food and agricultural wastes and convert them into biopolymers with inherently attractive properties such as biodegradability, biocompatibility, and appreciable mechanical and chemical properties. Such biopolymers can be applied to several fields such as packing, cosmetics, pharmaceutical, medical, biomedical, and agricultural. Thus, intending to elucidate the science of microbes to produce polymers, this review starts with a brief introduction to bioplastics by describing their importance and the methods for their production. The second section dives into the importance of bacteria regarding the biochemical routes for the synthesis of polymers along with their advantages and disadvantages. The third section covers some of the main parameters that influence biopolymers' production. Some of the main applications of biopolymers along with a comparison between the polymers obtained from microorganisms and the petrochemical-based ones are presented. Finally, some discussion about the future aspects and main challenges in this field is provided to elucidate the main issues that should be tackled for the wide application of microorganisms for the preparation of bioplastics.

From Nature-Sourced Polysaccharide Particles to Advanced Functional Materials

Polysaccharides constitute over 90% of the carbohydrate mass in nature, which makes them a promising feedstock for manufacturing sustainable materials. Polysaccharide particles (PSPs) are used as effective scavengers, carriers of chemical and biological cargos, and building blocks for the fabrication of macroscopic materials. The biocompatibility and degradability of PSPs are advantageous for their uses as biomaterials with more environmental friendliness. This review highlights the progresses in PSP applications as advanced functional materials, by describing PSP extraction, preparation, and surface functionalization with a variety of functional groups, polymers, nanoparticles, and biologically active species. This review also outlines the fabrication of PSP-derived macroscopic materials, as well as their applications in soft robotics, sensing, scavenging, water harvesting, drug delivery, and bioengineering. The paper is concluded with an outlook providing perspectives in the development and applications of PSP-derived materials.

A Review on Hydrophobically Associated Alginates: Approaches and Applications

Alginates are linear anionic polysaccharides, which are well-known for their biocompatible, nontoxic, and biodegradable nature. The polymer consists of alternating units of β-(1 → 4)-linked D-mannuronic acid (M) and α-(1 → 4)-linked L-guluronic acid (G) that have hydroxyl and carboxyl groups as the main functional groups. As a large number of free carboxyl and hydroxyl groups are present in the polymeric chain, the polymer is predominantly hydrophilic. The food and pharmaceutical industries have been the most extensive utilizers of alginates to produce gelling and thickening agents. However, by imparting hydrophobicity to alginates, the range of applications can be widened. Although there are reviews on alginate and its chemical modifications, reviews focusing on hydrophobically associated alginates have not been presented. The commonly used chemical modifications to incorporate hydrophobicity include esterification, Ugi reaction, reductive amination, and graft copolymerization. The hydrophobically modified alginates play an important role in delivery of hydrophobic drugs and pesticides as the modification increases the affinity toward hydrophobic components and helps in their sustained release. Due to their nontoxic and edible nature, they find use in the food industry as emulsion stabilizer to stabilize oil-in-water emulsions and to improve creaming ability. Further, alginate-based materials such as membranes, aerogels, and films are hydrophobically modified to improve their functionality and applicability to water treatment and food packaging. This Review aims to highlight the important chemical modifications and methods that are done to impart hydrophobicity to alginate, and the applications of hydrophobically modified alginates in different sectors ranging from drug delivery to food packaging are discussed.

Alginate/hyaluronic acid-based systems as a new generation of wound dressings: A review

Skin is the largest organ of the human body, which acts as a protective barrier against pathogens. Therefore, a lot of research has been carried out on wound care and healing. Creating an ideal environment for wound healing and optimizing the local and systemic conditions of the patient play critical roles in successful wound care. Many products have been developed for improving the wound environment and providing a protected and moist area for fast healing. However, there is still high demand for new systems with high efficiency. The first generation of wound dressings merely covered the wound, while the subsequent/last generations covered it and aided in healing it in different ways. In modern wound dressings, the kind of used materials and their complexity play a crucial role in the healing process. These new systems support wound healing by lowering inflammation, exudate, slough, and bacteria. This study addresses a review of alginate/hyaluronic acid-based wound dressings developed so far as well as binary and ternary systems and their role in wound healing. Our review corroborates that these systems can open up a new horizon for wounds that do not respond to usual treatments and have a long curing period.

Enhancing Soil Resilience: Bacterial Alginate Hydrogel vs. Algal Alginate in Mitigating Agricultural Challenges

Erosion and tillage changes negatively the soil physical structure, which directly impacts agricultural systems and consequently food security. To mitigate these adverse modifications, different polymeric materials from synthetic and natural sources, have been used as soil conditioners to improve the hydro-mechanical behavior of affected soils. One of the most interesting and used natural polymers is the alginate hydrogel. Although commercially available alginate hydrogels are primarily sourced from algal, they can also be sourced from bacteria. The gelation capacity of these hydrogels is determined by their molecular properties, which, in turn, are influenced by the production conditions. Bacterial alginate hydrogel production offers the advantage of precise control over environmental conditions during cultivation and extraction, thereby maintaining and enhancing their molecular properties. This, in turn, results in higher molecular weight and improved gelation capacity. In this study, we compared the effects of bacterial alginate (BH) and algal alginate (AH) hydrogels over the mechanical, hydraulic, and structural behavior of coarse quartz sand as a model soil. Mechanically, it was observed that the treatment with the lowest concentration of bacteria alginate hydrogel (BH1) reached higher values of yield strength, Young's modulus (E), shear modulus (G) and strain energy (U) than those treatments with algal alginate hydrogel (AH). Furthermore, the increase in the aggregate stability could be associated with the improvement of mechanical parameters. On the other hand, a greater water retention capacity was observed in the BH treatments, as well as a greater decrease in hydraulic conductivity with respect to the AH and control treatments. All these changes could be explained by the formation of bridge-like structures between the sand particles and the hydrogel, and this alteration may result in a shift in the mechanical and wettability characteristics of the treated soils. Finally, our findings emphasize the superior impact of bacterial alginate hydrogel on enhancing the mechanical and hydraulic properties of coarse quartz sand compared to traditional algal alginate. Besides, the use of bacterial alginate hydrogel could be useful to counteract erosion and water scarcity scenarios in agricultural systems.

Smart stimuli-responsive polysaccharide nanohydrogels for drug delivery: a review

Polysaccharides have found extensive utilization as biomaterials in drug delivery systems owing to their remarkable biocompatibility, simple functionalization, and inherent biological properties. Within the array of polysaccharide-based biomaterials, there is a growing fascination for self-assembled polysaccharide nanogels (NG) due to their ease of preparation and enhanced appeal across diverse biomedical appliances. Nanogel (or nanohydrogel), networks of nanoscale dimensions, are created by physically or chemically linking polymers together and have garnered immense interest as potential carriers for delivering drugs due to their favorable attributes. These include biocompatibility, high stability, the ability to adjust particle size, the capacity to load drugs, and their inherent potential to modify their surface to actively target specific cells or tissues via the attachment of ligands that can recognize corresponding receptors. Nanogels can be engineered to respond to specific stimuli, such as pH, temperature, light, or redox conditions, allowing controlled release of the encapsulated drugs. This intelligent targeting capability helps prevent drug accumulation in unintended tissues and reduces the potential side effects. Herein, an overview of nanogels is offered, comprising their methods of preparation and the design of stimulus-responsive nanogels that enable controlled release of drugs in response to specific stimuli.

Polysaccharides, proteins, and synthetic polymers based multimodal hydrogels for various biomedical applications: A review

Nature-derived or biologically encouraged hydrogels have attracted considerable interest in numerous biomedical applications owing to their multidimensional utility and effectiveness. The internal architecture of a hydrogel network, the chemistry of the raw materials involved, interaction across the interface of counter ions, and the ability to mimic the extracellular matrix (ECM) govern the clinical efficacy of the designed hydrogels. This review focuses on the mechanistic viewpoint of different biologically driven/inspired biomacromolecules that encourages the architectural development of hydrogel networks. In addition, the advantage of hydrogels by mimicking the ECM and the significance of the raw material selection as an indicator of bioinertness is deeply elaborated in the review. Furthermore, the article reviews and describes the application of polysaccharides, proteins, and synthetic polymer-based multimodal hydrogels inspired by or derived from nature in different biomedical areas. The review discusses the challenges and opportunities in biomaterials along with future prospects in terms of their applications in biodevices or functional components for human health issues. This review provides information on the strategy and inspiration from nature that can be used to develop a link between multimodal hydrogels as the main frame and its utility in biomedical applications as the primary target.

Synthesis and Evaluation of Alginate-Based Nanogels as Sustained Drug Carriers for Caffeine

The objective of this study is to design a polymeric network of nanogels for sustained release of caffeine. Therefore, alginate-based nanogels were fabricated by a free-radical polymerization technique for the sustained delivery of caffeine. Polymer alginate was crosslinked with monomer 2-acrylamido-2-methylpropanesulfonic acid by crosslinker N',N'-methylene bisacrylamide. The prepared nanogels were subjected to sol-gel fraction, polymer volume fraction, swelling, drug loading, and drug release studies. A high gel fraction was seen with the increasing feed ratio of polymer, monomer, and crosslinker. Greater swelling and drug release were observed at pH 4.6 and 7.4 as compared to pH 1.2 due to the deprotonation and protonation of functional groups of alginate and 2-acrylamido-2-methylpropanesulfonic acid. An increase was observed in swelling, loading, and release of the drug with the incorporation of a high feed ratio of polymer and monomer, while a reduction was seen with the increase in crosslinker feed ratio. Similarly, an HET-CAM test was used to evaluate the safety of the prepared nanogels, which showed that the prepared nanogels have no toxic effect on the chorioallantoic membrane of fertilized chicken eggs. Similarly, different characterizations techniques such as FTIR, DSC, SEM, and particle size analysis were carried out to determine the development, thermal stability, surface morphology, and particle size of the synthesized nanogels, respectively. Thus, we can conclude that the prepared nanogels can be used as a suitable agent for the sustained release of caffeine.

Alginate: Microbial production, functionalization, and biomedical applications

Alginates are natural polysaccharides widely participating in food, pharmaceutical, and environmental applications due to their excellent gelling capacity. Their excellent biocompatibility and biodegradability further extend their application to biomedical fields. The low consistency in molecular weight and composition of algae-based alginates may limit their performance in advanced biomedical applications. It makes microbial alginate production more attractive due to its potential for customizing alginate molecules with stable characteristics. Production costs remain the primary factor limiting the commercialization of microbial alginates. However, carbon-rich wastes from sugar, dairy, and biodiesel industries may serve as potential substitutes for pure sugars for microbial alginate production to reduce substrate costs. Fermentation parameter control and genetic engineering strategies may further improve the production efficiency and customize the molecular composition of microbial alginates. To meet the specific needs of biomedical applications, alginates may need functionalization, such as functional group modifications and crosslinking treatments, to achieve enhanced mechanical properties and biochemical activities. The development of alginate-based composites incorporated with other polysaccharides, gelatin, and bioactive factors can integrate the advantages of each component to meet multiple requirements in wound healing, drug delivery, and tissue engineering applications. This review provided a comprehensive insight into the sustainable production of high-value microbial alginates. It also discussed recent advances in alginate modification strategies and alginate-based composites for representative biomedical applications.

Yeast extracts from different manufacturers and supplementation of amino acids and micro elements reveal a remarkable impact on alginate production by A. vinelandii ATCC9046

BACKGROUND

In research and production, reproducibility is a key factor, to meet high quality and safety standards and maintain productivity. For microbial fermentations, complex substrates and media components are often used. The complex media components can vary in composition, depending on the lot and manufacturing process. These variations can have an immense impact on the results of biological cultivations. The aim of this work was to investigate and characterize the influence of the complex media component yeast extract on cultivations of Azotobacter vinelandii under microaerobic conditions. Under these conditions, the organism produces the biopolymer alginate. The focus of the investigation was on the respiration activity, cell growth and alginate production.

RESULTS

Yeast extracts from 6 different manufacturers and 2 different lots from one manufacturer were evaluated. Significant differences on respiratory activity, growth and production were observed. Concentration variations of three different yeast extracts showed that the performance of poorly performing yeast extracts can be improved by simply increasing their concentration. On the other hand, the results with well-performing yeast extracts seem to reach a saturation, when their concentration is increased. Cultivations with poorly performing yeast extract were supplemented with grouped amino acids, single amino acids and micro elements. Beneficial results were obtained with the supplementation of copper sulphate, cysteine or a combination of both. Furthermore, a correlation between the accumulated oxygen transfer and the final viscosity (as a key performance indicator), was established.

CONCLUSION

The choice of yeast extract is crucial for A. vinelandii cultivations, to maintain reproducibility and comparability between cultivations. The proper use of specific yeast extracts allows the cultivation results to be specifically optimised. In addition, supplements can be applied to modify and improve the properties of the alginate. The results only scratch the surface of the underlying mechanisms, as they are not providing explanations on a molecular level. However, the findings show the potential of optimising media containing yeast extract for alginate production with A. vinelandii, as well as the potential of targeted supplementation of the media.

Bacterial extracellular polymeric substances: Biosynthesis and interaction with environmental pollutants

Extracellular polymeric substances (EPS) are highly hydrated matrices produced by bacteria, containing various polymers such as polysaccharides, proteins, lipids, and DNA. Extracellular polymer concentrations, ions, and functional groups provide physical stability to the EPS. Constituents of EPS form the three-dimensional architecture and help acquire nutrition for the bacteria. Structural and functional diversity of the extracellular polymer depends on the specific glycosyltransferases, polymerase and transporter proteins. These enzymes are encoded by specific genes present in operons such as crd, alg, wca, and gum reported in Agrobacterium, Pseudomonas, Enterobacteriaceae, and Xanthomonas. The operons regulate the biosynthesis of extracellular polymers such as curdlan, alginate, colonic acid, and xanthan, respectively. Various functional groups in the EPS, such as carbonyl, hydroxyl, phosphoryl, and amide, provide the sorption site for interaction with environmental pollutants. Hydrophobic interactions and coordinate bonds mainly dominate the binding of EPS with environmental pollutants. EPS binds, emulsifies, and solubilizes the organic compounds, enhancing the degradation process. EPS binds with heavy metals through complexation, surface adsorption, precipitation, and ion exchange mechanisms. The biodegradability efficiency and nontoxicity properties of EPS make it an excellent biopolymer for decontaminating environmental pollutants. This review summarizes an overview of the biosynthetic mechanisms and interaction of the bacterial extracellular polymer with environmental pollutants. Interaction mechanisms of pollutants with EPS and EPS-mediated bioremediation will help develop removal applications. Moreover, understanding the genes responsible for EPS production, and implementation of new genetic methodology can be helpful for the enhanced biosynthesis of EPS to control pollution by sequestrating more environmental pollutants.

Identification of Pseudomonas aeruginosa exopolysaccharide Psl in biofilms using 3D OrbiSIMS

Secondary ion mass spectrometry (SIMS) offers advantages over both liquid extraction mass spectrometry and matrix assisted laser desorption mass spectrometry in that it provides the direct in situ analysis of molecules and has the potential to preserve the 3D location of an analyte in a sample. Polysaccharides are recognized as challenging analytes in the mass spectrometry of liquids and are also difficult to identify and assign using SIMS. Psl is an exopolysaccharide produced by Pseudomonas aeruginosa, which plays a key role in biofilm formation and maturation. In this Letter, we describe the use of the OrbiTrap analyzer with SIMS (3D OrbiSIMS) for the label-free mass spectrometry of Psl, taking advantage of its high mass resolving power for accurate secondary ion assignment. We study a P. aeruginosa biofilm and compare it with purified Psl to enable the assignment of secondary ions specific to the Psl structure. This resulted in the identification of 17 peaks that could confidently be ascribed to Psl fragments within the biofilm matrix. The complementary approach of the following neutral loss sequences is also shown to identify multiple oligosaccharide fragments without the requirement of a biological reference sample.

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.

Alginate-Based Materials Loaded with Nanoparticles in Wound Healing

Alginate is a naturally derived polysaccharide widely applied in drug delivery, as well as regenerative medicine, tissue engineering and wound care. Due to its excellent biocompatibility, low toxicity, and the ability to absorb a high amount of exudate, it is widely used in modern wound dressings. Numerous studies indicate that alginate applied in wound care can be enhanced with the incorporation of nanoparticles, revealing additional properties beneficial in the healing process. Among the most extensively explored materials, composite dressings with alginate loaded with antimicrobial inorganic nanoparticles can be mentioned. However, other types of nanoparticles with antibiotics, growth factors, and other active ingredients are also investigated. This review article focuses on the most recent findings regarding novel alginate-based materials loaded with nanoparticles and their applicability as wound dressings, with special attention paid to the materials of potential use in the treatment of chronic wounds.

Antimicrobial Nano-Zinc Oxide Biocomposites for Wound Healing Applications: A Review

Chronic wounds are a major concern for global health, affecting millions of individuals worldwide. As their occurrence is correlated with age and age-related comorbidities, their incidence in the population is set to increase in the forthcoming years. This burden is further worsened by the rise of antimicrobial resistance (AMR), which causes wound infections that are increasingly hard to treat with current antibiotics. Antimicrobial bionanocomposites are an emerging class of materials that combine the biocompatibility and tissue-mimicking properties of biomacromolecules with the antimicrobial activity of metal or metal oxide nanoparticles. Among these nanostructured agents, zinc oxide (ZnO) is one of the most promising for its microbicidal effects and its anti-inflammatory properties, and as a source of essential zinc ions. This review analyses the most recent developments in the field of nano-ZnO–bionanocomposite (nZnO-BNC) materials—mainly in the form of films, but also hydrogel or electrospun bandages—from the different preparation techniques to their properties and antibacterial and wound-healing performances. The effect of nanostructured ZnO on the mechanical, water and gas barrier, swelling, optical, thermal, water affinity, and drug-release properties are examined and linked to the preparation methods. Antimicrobial assays over a wide range of bacterial strains are extensively surveyed, and wound-healing studies are finally considered to provide a comprehensive assessment framework. While early results are promising, a systematic and standardised testing procedure for the comparison of antibacterial properties is still lacking, partly because of a not-yet fully understood antimicrobial mechanism. This work, therefore, allowed, on one hand, the determination of the best strategies for the design, engineering, and application of n-ZnO-BNC, and, on the other hand, the identification of the current challenges and opportunities for future research.

Computational modeling of the molecular basis for the calcium-dependence of the mannuronan C-5 epimerase AvAlgE6 from Azotobacter vinelandii

The mannuronan C-5 epimerases catalyze epimerization of β-d-mannuronic acid to α-l-guluronic acid in alginate polymers. The seven extracellular Azotobacter vinelandii epimerases (AvAlgE1-7) are calcium-dependent, and calcium is essential for the structural integrity of their carbohydrate binding R-modules. Ca²⁺ is also found in the crystal structures of the A-modules, where it is suggested to play a structural role. In this study, the structure of the catalytic A-module of the A. vinelandii mannuronan C-5 epimerase AvAlgE6 is used to investigate the role of this Ca²⁺. Molecular dynamics (MD) simulations with and without calcium reveal the possible importance of the bound Ca²⁺ in the hydrophobic packing of β-sheets. In addition, a putative calcium binding site is found in the active site, indicating a potential direct role of this calcium in the catalysis. According to the literature, two of the residues coordinating calcium in this site are essential for the activity. MD simulations of the interaction with bound substrate indicate that the presence of a calcium ion in this binding site increases the binding strength. Further, explicit calculations of the substrate dissociation pathways with umbrella sampling simulations show and energetically higher dissociation barrier when calcium is present. The present study eludes to a putative catalytic role of calcium in the charge neutralizing first step of the enzymatic reaction. In addition to the importance for understanding these enzymes' molecular mechanisms, this could have implications for engineering strategies of the epimerases in industrial alginate processing.

Natural Gums in Drug-Loaded Micro- and Nanogels

Gums are polysaccharide compounds obtained from natural sources, such as plants, algae and bacteria. Because of their excellent biocompatibility and biodegradability, as well as their ability to swell and their sensitivity to degradation by the colon microbiome, they are regarded as interesting potential drug carriers. In order to obtain properties differing from the original compounds, blends with other polymers and chemical modifications are usually applied. Gums and gum-derived compounds can be applied in the form of macroscopic hydrogels or can be formulated into particulate systems that can deliver the drugs via different administration routes. In this review, we present and summarize the most recent studies regarding micro- and nanoparticles obtained with the use of gums extensively investigated in pharmaceutical technology, their derivatives and blends with other polymers. This review focuses on the most important aspects of micro- and nanoparticulate systems formulation and their application as drug carriers, as well as the challenges related to these formulations.

Alginates Combined with Natural Polymers as Valuable Drug Delivery Platforms

Alginates (ALG) have been used in biomedical and pharmaceutical technologies for decades. ALG are natural polymers occurring in brown algae and feature multiple advantages, including biocompatibility, low toxicity and mucoadhesiveness. Moreover, ALG demonstrate biological activities per se, including anti-hyperlipidemic, antimicrobial, anti-reflux, immunomodulatory or anti-inflammatory activities. ALG are characterized by gelling ability, one of the most frequently utilized properties in the drug form design. ALG have numerous applications in pharmaceutical technology that include micro- and nanoparticles, tablets, mucoadhesive dosage forms, wound dressings and films. However, there are some shortcomings, which impede the development of modified-release dosage forms or formulations with adequate mechanical strength based on pure ALG. Other natural polymers combined with ALG create great potential as drug carriers, improving limitations of ALG matrices. Therefore, in this paper, ALG blends with pectins, chitosan, gelatin, and carrageenans were critically reviewed.

Optimization of Antibacterial, Structures, and Thermal Properties of Alginate-ZrO2 Bionanocomposite by the Taguchi Method

Developing novel antibacterial chemicals is constantly necessary since bacterial resistance to antibiotics is an inevitable occurrence. This research aimed to find the ideal conditions for using antibacterial zirconia (ZrO2) NPs with polymer alginate nanocomposites. Using the Taguchi method, alginate biopolymer, zirconia NPs, and stirring time were utilized to construct nine nanocomposites. Analysis of Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-vis), spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA) indicated the development of nanocomposites with appropriate structural properties. Antibacterial efficacy against Streptococcus mutans (S. mutans) biofilm was the highest when the nanocomposite was formed under the circumstances of experiment 6 (zirconia 8 mg/ml, alginate 70 mg/ml, and 40 min stirring time). Alginate/zirconia bionanocomposites generated using the in situ technique proved efficient against S. mutans. Nanoparticles have a high surface-to-volume ratio and surface energy, which can cause them to agglomerate and make their antimicrobial effectiveness problematic. Using zirconia nanoparticles in an alginate polymer matrix in the form of nanocomposite can increase the stability of nanoparticles. Due to the advantageous antibacterial qualities of this bionanocomposite, it can be utilized in various medical materials and dental appliances.

Characterization of a Novel Alginate Lyase with Two Alginate Lyase Domains from the Marine Bacterium Vibrio sp. C42

Alginate is abundant in the cell walls of brown algae. Alginate lyases can degrade alginate, and thus play an important role in the marine carbon cycle and industrial production. Currently, most reported alginate lyases contain only one functional alginate lyase domain. AlyC8 is a putative alginate lyase with two alginate lyase domains (CD1 and CD2) from the marine alginate-degrading strain Vibrio sp. C42. To characterize AlyC8 and its two catalytic domains, AlyC8 and its two catalytic domain-deleted mutants, AlyC8-CD1 and AlyC8-CD2, were expressed in Escherichia coli. All three proteins have noticeable activity toward sodium alginate and exhibit optimal activities at pH 8.0-9.0 and at 30-40 °C, demonstrating that both CD1 and CD2 are functional. However, CD1 and CD2 showed opposite substrate specificity. The differences in substrate specificity and degradation products of alginate between the mutants and AlyC8 demonstrate that CD1 and CD2 can act synergistically to enable AlyC8 to degrade various alginate substrates into smaller oligomeric products. Moreover, kinetic analysis indicated that AlyC8-CD1 plays a major role in the degradation of alginate by AlyC8. These results demonstrate that AlyC8 is a novel alginate lyase with two functional catalytic domains that are synergistic in alginate degradation, which is helpful for a better understanding of alginate lyases and alginate degradation.

Biomolecule-Based Optical Metamaterials: Design and Applications

Metamaterials are broadly defined as artificial, electromagnetically homogeneous structures that exhibit unusual physical properties that are not present in nature. They possess extraordinary capabilities to bend electromagnetic waves. Their size, shape and composition can be engineered to modify their characteristics, such as iridescence, color shift, absorbance at different wavelengths, etc., and harness them as biosensors. Metamaterial construction from biological sources such as carbohydrates, proteins and nucleic acids represents a low-cost alternative, rendering high quantities and yields. In addition, the malleability of these biomaterials makes it possible to fabricate an endless number of structured materials such as composited nanoparticles, biofilms, nanofibers, quantum dots, and many others, with very specific, invaluable and tremendously useful optical characteristics. The intrinsic characteristics observed in biomaterials make them suitable for biomedical applications. This review addresses the optical characteristics of metamaterials obtained from the major macromolecules found in nature: carbohydrates, proteins and DNA, highlighting their biosensor field use, and pointing out their physical properties and production paths.

Direct production of polyhydroxybutyrate and alginate from crude glycerol by Azotobacter vinelandii using atmospheric nitrogen

While biodiesel is drawing attention as an eco-friendly fuel, the use of crude glycerol, a byproduct of the fuel production process, has increasingly become a concern to be addressed. Here we show the development of a low-cost fermentation technology using an atmospheric nitrogen-fixing bacterium to recycle crude glycerol into functional biopolymers. Azotobacter vinelandii showed substantial growth on tap water-diluted crude glycerol without any pretreatment. The number of viable A. vinelandii cells increased over 1000-fold under optimal growth conditions. Most of the glycerol content (~ 0.2%) in the crude glycerol medium was completely depleted within 48 h of culture. Useful polymers, such as polyhydroxybutyrate and alginate, were also produced. Polyhydroxybutyrate productivity was increased ten-fold by blocking the alginate synthesis pathway. Although there are few examples of using crude glycerol directly as a carbon source for microbial fermentation, there are no reports on the use of crude glycerol without the addition of a nitrogen source. This study demonstrated that it is possible to develop a technology to produce industrially useful polymers from crude glycerol through energy-saving and energy-efficient fermentation using the atmospheric nitrogen-fixing microorganism A. vinelandii.

Genetic Regulation of Alginate Production in Azotobacter vinelandii a Bacterium of Biotechnological Interest: A Mini-Review

Alginates are a family of polymers composed of guluronate and mannuronate monomers joined by β (1–4) links. The different types of alginates have variations in their monomer content and molecular weight, which determine the rheological properties and their applications. In industry, alginates are commonly used as additives capable of viscosifying, stabilizing, emulsifying, and gelling aqueous solutions. Recently, additional specialized biomedical uses have been reported for this polymer. Currently, the production of alginates is based on the harvesting of seaweeds; however, the composition and structure of the extracts are highly variable. The production of alginates for specialized applications requires a precise composition of monomers and molecular weight, which could be achieved using bacterial production systems such as those based on Azotobacter vinelandii, a free-living, non-pathogenic bacterium. In this mini-review, we analyze the latest advances in the regulation of alginate synthesis in this model.

HrgS (Avin 34990), a novel histidine-kinase related to GacS, regulates alginate synthesis in Azotobacter vinelandii

Azotobacter vinelandii is a soil bacterium that produces alginates, a family of polymers of biotechnological interest. In A. vinelandii, alginate production is controlled by the two-component system GacS/GacA. GacS/GacA, in turn, regulates the Rsm post-transcriptional regulatory system establishing a cascade that regulates alginate biosynthesis by controlling the expression of the algD biosynthetic gene. In Pseudomonas aeruginosa, GacS/GacA is influenced by other histidine-kinases constituting a multicomponent signal transduction system. In this study, we explore the presence of GacS-related histidine-kinases in A. vinelandii and discover a novel histidine-kinase (Avin_34990, renamed HrgS). This histidin-kinase acts as a negative regulator of alginate synthesis by controlling the transcription of the sRNAs belonging to the Rsm post-transcriptional regulatory system, for which a functional GacS is required.

Bacterial Alginate-Based Hydrogel Reduces Hydro-Mechanical Soil-Related Problems in Agriculture Facing Climate Change

Agricultural systems are facing the negative impacts of erosion and water scarcity, directly impacting the hydro-mechanical behavior of soil aggregation. Several technologies have been proposed to reduce hydro-mechanical soil-related problems in agriculture. Biopolymer-based hydrogels have been reported to be a great tool to tackle these problems in soils. In this study, we investigated the hydro-mechanical behavior of different soils media treated with Ca-bacterial alginate hydrogel. We used an unconfined uniaxial compression test, aggregate stability test and hydraulic conductivity measurements to investigate the mechanical and hydraulic behavior of treated soils media. Our results from unconfined uniaxial compression test showed that yield stress (i.e., strength) increased in treated soils with higher kaolinite and water content (i.e., HCM3), compared with untreated coarse quartz sand (i.e., CM1). Furthermore, we found that temperature is an important factor in the gelation capacity of our hydrogel. At room temperature, HCM3 displayed the higher aggregate stability, almost 5.5-fold compared with treated coarse quartz sand (HCM1), while this differential response was not sustained at warm temperature. In general, the addition of different quantities of kaolinite decreased the saturated hydraulic conductivity for all treatments. Finally, bright field microscopy imaging represents the soil media matrix between sand and clay particles with Ca-bacterial alginate hydrogel that modify the hydro-mechanical behavior of different soils media. The results of this study could be helpful for the soil-related problems in agriculture facing the negative effects of climate change.

A Novel Alginate Lyase: Identification, Characterization, and Potential Application in Alginate Trisaccharide Preparation

Alginate oligosaccharides (AOS) have many biological activities and significant applications in prebiotics, nutritional supplements, and plant growth development. Alginate lyases have unique advantages in the preparation of AOS. However, only a limited number of alginate lyases have been so far reported to have potentials in the preparation of AOS with specific degrees of polymerization. Here, an alginate-degrading strain Pseudoalteromonasarctica M9 was isolated from Sargassum, and five alginate lyases were predicted in its genome. These putative alginate lyases were expressed and their degradation products towards sodium alginate were analyzed. Among them, AlyM2 mainly generated trisaccharides, which accounted for 79.9% in the products. AlyM2 is a PL6 lyase with low sequence identity (≤28.3%) to the characterized alginate lyases and may adopt a distinct catalytic mechanism from the other PL6 alginate lyases based on sequence alignment. AlyM2 is a bifunctional endotype lyase, exhibiting the highest activity at 30 °C, pH 8.0, and 0.5 M NaCl. AlyM2 predominantly produces trisaccharides from homopolymeric M block (PM), homopolymeric G block (PG), or sodium alginate, with a trisaccharide production of 588.4 mg/g from sodium alginate, indicating its promising potential in preparing trisaccharides from these polysaccharides.

The Regulatory Hierarchy Following Signal Integration by the CbrAB Two-Component System: Diversity of Responses and Functions

CbrAB is a two-component system, unique to bacteria of the family Pseudomonaceae, capable of integrating signals and involved in a multitude of physiological processes that allow bacterial adaptation to a wide variety of varying environmental conditions. This regulatory system provides a great metabolic versatility that results in excellent adaptability and metabolic optimization. The two-component system (TCS) CbrA-CbrB is on top of a hierarchical regulatory cascade and interacts with other regulatory systems at different levels, resulting in a robust output. Among the regulatory systems found at the same or lower levels of CbrAB are the NtrBC nitrogen availability adaptation system, the Crc/Hfq carbon catabolite repression cascade in Pseudomonas, or interactions with the GacSA TCS or alternative sigma ECF factor, such as SigX. The interplay between regulatory mechanisms controls a number of physiological processes that intervene in important aspects of bacterial adaptation and survival. These include the hierarchy in the use of carbon sources, virulence or resistance to antibiotics, stress response or definition of the bacterial lifestyle. The multiple actions of the CbrAB TCS result in an important competitive advantage.

The seaweed holobiont: from microecology to biotechnological applications

In the ocean, seaweed and microorganisms have coexisted since the earliest stages of evolution and formed an inextricable relationship. Recently, seaweed has attracted extensive attention worldwide for ecological and industrial purposes, but the function of its closely related microbes is often ignored. Microbes play an indispensable role in different stages of seaweed growth, development and maturity. A very diverse group of seaweed‐associated microbes have important functions and are dynamically reconstructed as the marine environment fluctuates, forming an inseparable ‘holobiont’ with their host. To further understand the function and significance of holobionts, this review first reports on recent advances in revealing seaweed‐associated microbe spatial and temporal distribution. Then, this review discusses the microbe and seaweed interactions and their ecological significance, and summarizes the current applications of the seaweed–microbe relationship in various environmental and biological technologies. Sustainable industries based on seaweed holobionts could become an integral part of the future bioeconomy because they can provide more resource‐efficient food, high‐value chemicals and medical materials. Moreover, holobionts may provide a new approach to marine environment restoration.

Sodium Alginate as a Pharmaceutical Excipient: Novel Applications of a Well-known Polymer

Alginates are naturally occurring polymers revealing low toxicity, good biocompatibility and biodegradability, excellent gelling and thickening properties, as well as low production cost and good availability. One of the most important features typical for alginates is the ability to undergo ionotropic gelation which is gel formation process occurring upon the contact with cations. Because of their advantageous properties, alginates have been extensively utilized in food and pharmaceutical industries. In this review the current knowledge regarding the most recent studies involving both popularly applied dosage forms, like tablets or hydrogels, and novel advanced drug delivery systems applied in targeted therapies are summarized and discussed. The presented studies indicate that although sodium alginate is a well-established polymer, it is still widely applied as pharmaceutical excipient and the presented research studies indicate that there are still research areas that can be explored and provide innovation in drug delivery systems.

Competitive Biosynthesis of Bacterial Alginate Using Azotobacter vinelandii 12 for Tissue Engineering Applications

This study investigated the effect of various cultivation conditions (sucrose/phosphate concentrations, aeration level) on alginate biosynthesis using the bacterial producing strain Azotobacter vinelandii 12 by the full factorial design (FFD) method and physicochemical properties (e.g., rheological properties) of the produced bacterial alginate. We demonstrated experimentally the applicability of bacterial alginate for tissue engineering (the cytotoxicity testing using mesenchymal stem cells (MSCs)). The isolated synthesis of high molecular weight (M_w) capsular alginate with a high level of acetylation (25%) was achieved by FFD method under a low sucrose concentration, an increased phosphate concentration, and a high aeration level. Testing the viscoelastic properties and cytotoxicity showed that bacterial alginate with a maximal M_w (574 kDa) formed the densest hydrogels (which demonstrated relatively low cytotoxicity for MSCs in contrast to bacterial alginate with low M_w). The obtained data have shown promising prospects in controlled biosynthesis of bacterial alginate with different physicochemical characteristics for various biomedical applications including tissue engineering.

Applications of Microbial Exopolysaccharides in the Food Industry

Exopolysaccharides (EPSs) are high molecular weight polysaccharides secreted by microorganisms in the surrounding environment. In addition to the favorable benefits of these compounds for microorganisms, including microbial cell protection, they are used in various food, pharmaceutical, and cosmetic industries. Investigating the functional and health-promoting characteristics of microbial EPS, identifying the isolation method of these valuable compounds, and their applications in the food industry are the objectives of this study. EPS are used in food industries as thickeners, gelling agents, viscosifiers, and film formers. The antioxidative, anticancer, prebiotic, and cholesterol-lowering effects of some of these compounds make it possible to use them in functional food production.

Fabrication of alginate based microgels for drug-sustained release: In-vitro and in-vivo evaluation

The current study was conducted to evaluate and analyze the effect of alginate, itaconic acid, and N,N'-methylene bisacrylamide in formulation of a novel alginate based microgels for sustained release of theophylline. The fabricated microgels were characterized by PXRD, SEM, FTIR, TGA and DSC respectively. FTIR revealed that alginate reacted with itaconic acid during polymerization reaction and confirmed the overlapping of itaconic acid on the backbone of alginate. TGA and DSC depicted high thermal stability of the fabricated microgels as compared to pure unreacted polymer and monomer. Likewise, dynamic swelling and percent drug release studies were carried out at different pH media i.e., pH 1.2, 4.6 and 7.4 respectively. Greater dynamic swelling and percent drug release was observed at higher pH 7.4 as compared to lower pH 4.6 and 1.2 due to the deprotonation of COOH groups of both alginate and itaconic acid respectively. The drug release mechanism from the fabricated microgels could be described by first order model. In-vivo pharmacokinetic study was performed on rabbits and exhibited sustained release in rabbits. Hence, the developed microgels indicated higher potential as the delivery system for the sustained delivery of theophylline.

Sodium alginate and alginic acid as pharmaceutical excipients for tablet formulation: Structure-function relationship

Alginic acid and its sodium salt are well-accepted pharmaceutical excipients fulfilling several roles in the development of solid oral dosage forms. Although they have attractive advantages as safety, abundance, relatively low cost and biodegradability, these natural polysaccharides possess a high variability that may limit their use as excipients for tablet formulation. Thus, to obtain robust formulations and high-quality drug products with consistent performance a complete understanding of the structure-property relationship becomes necessary as the structure of alginates affects both, technological and biopharmaceutical properties. This review compiles the compaction studies carried out that relate the structure of alginates to their mechanical and dissolution performances. The different analytical methods used to determine the chemical composition, primary structure and molecular weight distribution, major factors affecting the behavior of alginates in direct compression, are also exposed. Finally, different strategies reported to improve the properties of alginic acid as direct compression excipient are discussed.

The Usages and Potential Uses of Alginate for Healthcare Applications

Due to their unique properties, alginate-based biomaterials have been extensively used to treat different diseases, and in the regeneration of diverse organs. A lot of research has been done by the different scientific community to develop biofilms for fulfilling the need for sustainable human health. The aim of this review is to hit upon a hydrogel enhancing the scope of utilization in biomedical applications. The presence of active sites in alginate hydrogels can be manipulated for managing various non-communicable diseases by encapsulating, with the bioactive component as a potential site for chemicals in developing drugs, or for delivering macromolecule nutrients. Gels are accepted for cell implantation in tissue regeneration, as they can transfer cells to the intended site. Thus, this review will accelerate advanced research avenues in tissue engineering and the potential of alginate biofilms in the healthcare sector.

Antiviral Properties of Alginate-Based Biomaterials: Promising Antiviral Agents against SARS-CoV-2

The COVID-19 pandemic has made it essential to explore alternative antiviral materials. Alginate is a biodegradable, renewable, biocompatible, water-soluble and antiviral biopolymer with many potential biomedical applications. In this regard, this review shows 17 types of viruses that have been tested in contact with alginate and its related biomaterials. Most of these studies show that alginate-based materials possess little or no toxicity and are able to inhibit a wide variety of viruses affecting different organisms: in humans by the human immunodeficiency virus type 1, the hepatitis A, B, and C viruses, Sindbis virus, herpes simplex virus type 1 and 2, poliovirus type 1, rabies virus, rubella virus, and the influenza virus; in mice by the murine norovirus; in bacteria by the T4 coliphage, and in plants by the tobacco mosaic virus and the potato virus X. Many of these are enveloped positive-sense single-stranded RNA viruses, like SARS-CoV-2, which render alginate-based materials highly promising in the COVID-19 pandemic.

Bacterial alginate metabolism: an important pathway for bioconversion of brown algae

Brown macroalgae have attracted great attention as an alternative feedstock for biorefining. Although direct conversion of ethanol from alginates (major components of brown macroalgae cell walls) is not amenable for industrial production, significant progress has been made not only on enzymes involved in alginate degradation, but also on metabolic pathways for biorefining at the laboratory level. In this article, we summarise recent advances on four aspects: alginate, alginate lyases, different alginate-degrading systems, and application of alginate lyases and associated pathways. This knowledge will likely inspire sustainable solutions for further application of both alginate lyases and their associated pathways.

Plant Nanomaterials and Inspiration from Nature: Water Interactions and Hierarchically Structured Hydrogels

Recent developments in the area of plant-based hydrogels are introduced, especially those derived from wood as a widely available, multiscale, and hierarchical source of nanomaterials, as well as other cell wall elements. With water being fundamental in a hydrogel, water interactions, hydration, and swelling, all critically important in designing, processing, and achieving the desired properties of sustainable and functional hydrogels, are highlighted. A plant, by itself, is a form of a hydrogel, at least at given states of development, and for this reason phenomena such as fluid transport, diffusion, capillarity, and ionic effects are examined. These aspects are highly relevant not only to plants, especially lignified tissues, but also to the porous structures produced after removal of water (foams, sponges, cryogels, xerogels, and aerogels). Thus, a useful source of critical and comprehensive information is provided regarding the synthesis of hydrogels from plant materials (and especially wood nanostructures), and about the role of water, not only for processing but for developing hydrogel properties and uses.

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

The use of biofertilizers, including biocontrol agents such as Pseudomonas and Bacillus in agriculture can increase soil characteristics and plant acquisition of nutrients and enhancement the efficiency of manure and mineral fertilizer. Despite the problems that liquid and solid formulations have in maintaining the viability of microbial agents, encapsulation can improve their application with extended shelf-life, and controlled release from formulations. Research into novel formulation methods especially encapsulation techniques has increased in recent years due to the mounting demand for microbial biological control. The application of polymeric materials in agriculture has developed recently as a replacement for traditional materials and considered an improvement in technological processes in the growing of crops. This study aims to overview of types of biopolymers and methods used for encapsulation of living biological control agents, especially microbial organisms.

Approaches in Animal Proteins and Natural Polysaccharides Application for Food Packaging: Edible Film Production and Quality Estimation

Natural biopolymers are an interesting resource for edible films production, as they are environmentally friendly packaging materials. The possibilities of the application of main animal proteins and natural polysaccharides are considered in the review, including the sources, structure, and limitations of usage. The main ways for overcoming the limitations caused by the physico-chemical properties of biopolymers are also discussed, including composites approaches, plasticizers, and the addition of crosslinking agents. Approaches for the production of biopolymer-based films and coatings are classified according to wet and dried processes and considered depending on biopolymer types. The methods for mechanical, physico-chemical, hydration, and uniformity estimation of edible films are reviewed.