Fungal (1 → 3)-α-d-glucans as a new kind of biosorbent for heavy metals

Acceptor Subsite Mutants of Limosilactobacillus fermentum NCC 2970 GtfB 4,3-α-Glucanotransferase Regulate the Ratio of (α1 → 3)/(α1 → 6) Linkages in Biosynthesized α-Glucans

Limosilactobacillus fermentum NCC 2970 GtfB (Lf2970 GtfB) is the only characterized 4,3-α-glucanotransferase (4,3-α-GTase) in the glycoside hydrolase (GH) 70 family belonging to the GtfB subfamily. However, the mechanism for its (α1 → 3) linkage formation remains unclear, and the structural determinants of its linkage specificity remain to be explored. Here, sequence alignment and structural comparison were conducted to identify key amino acids that may be critical for linkage specificity. Five residues of Lf2970 GtfB (D991, G1028, A1398, T1400, and E1405), located at donor and acceptor subsites, were selected for mutation. Product structure analysis revealed that D991 and G1028, located near the acceptor binding subsites, played crucial roles in linkage formation. Besides native (α1 → 4) and (α1 → 3) linkages, mutants G1028R and D991N showed 8 and 10% (α1 → 6) linkage increases compared to 1% for wild-type in products. Additionally, molecular docking studies demonstrated that the orientation of acceptor binding in G1028R and D991N mutants was favorable for (α1 → 6) linkage synthesis. However, the mutation at positions A1398, T1400, and E1405 indicated that the donor subsites contribute less to the linkage specificity. These results shed light on the structural determinants of linkage specificity of 4,3-α-GTase Lf2970 GtfB and provided insights into the structure-function relationship of family GH70.

Structural Characterization and Biological Properties Analysis of Exopolysaccharides Produced by Weisella cibaria HDL-4

An exopolysaccharide (EPS)-producing strain, identified as Weissella cibaria HDL-4, was isolated from litchi. After separation and purification, the structure and properties of HDL-4 EPS were characterized. The molecular weight of HDL-4 EPS was determined to be 1.9 × 10⁶ Da, with glucose as its monosaccharide component. Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance (NMR) analyses indicated that HDL-4 EPS was a D-glucan with α-(1→6) and α-(1→4) glycosidic bonds. X-ray diffraction (XRD) analysis revealed that HDL-4 EPS was amorphous. Scanning electron microscope (SEM) and atomic force microscope (AFM) observations showed that HDL-4 EPS possesses pores, irregular protrusions, and a smooth layered structure. Additionally, HDL-4 EPS demonstrated significant thermal stability, remaining stable below 288 °C. It exhibited a strong metal ion adsorption activity, emulsification activity, antioxidant activity, and water-retaining property. Therefore, HDL-4 EPS can be extensively utilized in the food and pharmaceutical industries as an additive and prebiotic.

Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Hierarchical structure and chemical composition of complementary segments of the fruiting bodies of Fomes fomentarius fungi fine-tune the compressive properties

Humanity is often fascinated by structures and materials developed by Nature. While structural materials such as wood have been widely studied, the structural and mechanical properties of fungi are still largely unknown. One of the structurally interesting fungi is the polypore Fomes fomentarius. The present study deals with the investigation of the light but robust fruiting body of F. fomentarius. The four segments of the fruiting body (crust, trama, hymenium, and mycelial core) were examined. The comprehensive analysis included structural, chemical, and mechanical characterization with particular attention to cell wall composition, such as chitin/chitosan and glucan content, degree of deacetylation, and distribution of trace elements. The hymenium exhibited the best mechanical properties even though having the highest porosity. Our results suggest that this outstanding strength is due to the high proportion of skeletal hyphae and the highest chitin/chitosan content in the cell wall, next to its honeycomb structure. In addition, an increased calcium content was found in the hymenium and crust, and the presence of calcium oxalate crystals was confirmed by SEM-EDX. Interestingly, layers with different densities as well as layers of varying calcium and potassium depletion were found in the crust. Our results show the importance of considering the different structural and compositional characteristics of the segments when developing fungal-inspired materials and products. Moreover, the porous yet robust structure of hymenium is a promising blueprint for the development of advanced smart materials.

Exploring a GtfB-Type 4,6-α-Glucanotransferase to Synthesize the (α1 → 6) Linkages in Linear Chain and Branching Points from Amylose and Enhance the Functional Property of Granular Corn Starches

Starch-converting α-glucanotransferases of glycoside hydrolase family 70 (GH70) are promising enzymatic tools for the production of diverse α-glucans with (potential) commercial applications in food and health and as biomaterials. In this study, a novel GtfB enzyme from Weissella confusa MBF8-1 was screened in the National Center for Biotechnology Information (NCBI) nonredundant protein database. The enzyme (named WcMBF8-1 GtfB) displayed high conservation in motifs I-IV with other GtfB enzymes but possessed unique variations in several substrate-binding residues. Structural characterizations of its α-glucan products revealed that WcMBF8-1 GtfB exhibited an atypical 4,6-α-glucanotransferase activity and was capable of catalyzing, by cleaving off (α1 → 4)-linkages in starch-like substrates and the synthesis of linear (α1 → 6) linkages and (α1 → 4,6) branching points. The product specificity enlarges the diversity of α-glucans and facilitates recognition of the determinants of the linkage specificity in GtfB enzymes. Furthermore, the contents of slowly digestible starch and resistant starch of granular corn starches, modified by WcMBF8-1 GtfB, increased by 6.7%, which suggested the potential value for the utilization of WcMBF8-1 GtfB to prepare "clean-label" starch ingredients with improved functional attributes.

Alpha-glucan: a novel bacterial polysaccharide and its application as a biosorbent for heavy metals

This study identified an extracellular bacterial polysaccharide produced by Bacillus velezensis strain 40B that contains more than 90% of the monosaccharide glucose as alpha-glucan. A prominent peak at 1074 cm-1, a characteristic of glycoside couplings, was visible in the FTIR spectrum. There were traces of xylose, sucrose, and lactose, according to the HPLC study. The ability of this bacterial glucan to operate as a biosorbent of the heavy metals cobalt, chromium, copper, and lead from aqueous solutions was investigated in conjunction with Ca-alginate beads. It proved that glucan 40B has a low affinity for chromium ions and is selective for lead. Initial concentration measurements showed an inverse relationship between concentration and the amount of metal ions eliminated. Lead and chromium removal increased as the glucan dose was increased. It was shown that as the pH of the starting solution is elevated, there is an increase in the sorption of metal ions onto the glucan. It was clear that when the temperature increased, the fraction of metal ion sorption slightly increased. Glucan has a wide range of industrial applications, from food and medicine to health and nutrition. As a result, the investigation's scope was expanded to include heavy metal removal.

Plants, animals, and fisheries waste-mediated bioremediation of contaminants of environmental and emerging concern (CEECs)-a circular bioresource utilization approach

The release of contaminants of environmental concern including heavy metals and metalloids, and contaminants of emerging concern including organic micropollutants from processing industries, pharmaceuticals, personal care, and anthropogenic sources, is a growing threat worldwide. Mitigating inorganic and organic contaminants, which can be coined as contaminants of environmental and emerging concern (CEECs), is a big challenge as traditional physicochemical processes are not economically viable for managing mixed contaminants of low concentrations. As a result, low-cost materials must be designed to provide high CEEC removal efficiency. One of the environmentally viable and energy-efficient approaches is biosorption, which involves using biomass or biopolymers isolated from plants or animals to decontaminate heavy metals in contaminated environments using inherent biological mechanisms. Among chemical constituents in plant biomass, cellulose, lignin, hemicellulose, proteins, polysaccharides, phenolic compounds, and animal biomass include polysaccharides and other compounds to bind heavy metals covalently and non-covalently. These functional groups include carboxyl, hydroxyl, carbonyl, amide, amine, and sulfhydryl. Cation-exchange capacities of these bioadsorbents can be improved by applying chemical modifications. The relevance of chemical constituents and bioactives in biosorbents derived from agricultural production such as food and fodder crops, bioenergy and cash crops, fruit and vegetable crops, medicinal and aromatic plants, plantation trees, aquatic and terrestrial weeds, and animal production such as dairy, goatery, poultry, duckery, and fisheries is highlighted in this comprehensive review for sequestering and bioremediation of CEECs, including as many as ten different heavy metals and metalloids co-contaminated with other organic micropollutants in circular bioresource utilization and one-health concepts.

Fungal bioproducts for petroleum hydrocarbons and toxic metals remediation: recent advances and emerging technologies

Petroleum hydrocarbons and toxic metals are sources of environmental contamination and are harmful to all ecosystems. Fungi have metabolic and morphological plasticity that turn them into potential prototypes for technological development in biological remediation of these contaminants due to their ability to interact with a specific contaminant and/or produced metabolites. Although fungal bioinoculants producing enzymes, biosurfactants, polymers, pigments and organic acids have potential to be protagonists in mycoremediation of hydrocarbons and toxic metals, they can still be only adjuvants together with bacteria, microalgae, plants or animals in such processes. However, the sudden accelerated development of emerging technologies related to the use of potential fungal bioproducts such as bioinoculants, enzymes and biosurfactants in the remediation of these contaminants, has boosted fungal bioprocesses to achieve higher performance and possible real application. In this review, we explore scientific and technological advances in bioprocesses related to the production and/or application of these potential fungal bioproducts when used in remediation of hydrocarbons and toxic metals from an integral perspective of biotechnological process development. In turn, it sheds light to overcome existing technological limitations or enable new experimental designs in the remediation of these and other emerging contaminants.

Biosorption Characteristic and Cytoprotective Effect of Pb2+, Cu2+ and Cd2+ by a Novel Polysaccharide from Zingiber strioatum

The pollution of heavy metal ions can cause damage to the human body through food, so developing a new biocompatible material that can remove the damage of heavy metal ions has a good application prospect. In this study, we obtained a new homogeneous polysaccharide composed of seven monosaccharides from Zingiber strioatum by using the method of separation and purification of polysaccharide. The results of adsorption behavior showed that the concentration, temperature and pH value could affect the adsorption effect of Zingiber strioatum polysaccharide (ZSP). Through model fitting of the data of adsorption time and metal concentration, the pseudo second-order kinetic model can well describe the kinetics of the adsorption process, and the adsorption isotherm data fit well with the Langmuir model. In the preliminary research results of adsorption mechanism, SEM showed the appearance of ZSP as flake and porous surface; EDX analysis confirmed the metal adsorption capacity of ZSP. Meanwhile, XPS and FT-IR further clarified the adsorption based on functional groups composed of C and O. The cells preprotected by ZSP can resist heavy metal ions. The above results show that ZSP can be used as a new macromolecule to bind heavy metal ions, which can broaden the research scope of polysaccharides in contaminated food systems.

The Influence of Binding of Selected Mycotoxin Deactivators and Aflatoxin M1 on the Content of Selected Micronutrients in Milk

Milk containing aflatoxin M1 (ATM1) in quantities above 0.05 µg/kg is considered unsuitable for consumption. It is possible to use mycotoxin deactivators that bind aflatoxin M1 and allow the further use of milk. The study aimed to examine the impact of selected mycotoxin deactivators (beta-glucan from yeast and oats, and live and dead lactic acid bacteria) on the nutritional composition of milk after binding to aflatoxin M1 intentionally added to milk. The study used consumption milk with 2.8% milk fat intentionally contaminated with aflatoxin M1. Furthermore, 0.05% and 0.1% solutions of beta-glucan from yeast and beta-glucan from oats were added to the contaminated milk, as well as live and dead lactic acid. Concentrations of Na, K, Mg, and Ca were monitored at the zero hour of binding of mycotoxin deactivators and ATM1, after 2 h of binding, and after 4 and 24 h of binding. The largest deviations were found in Na, K, and Mg, while the minimum changes were observed in Ca. Live lactic acid bacteria were found to have the least impact on micronutrients, except in Na (difference = 40, p = 0.029, GES = 0.083), where the 0.1% solution from oats had the least impact on micronutrient content. The results of this study suggest that it is best to use live lactic acid bacteria where the different duration of action regarding nutrients, with the possible exception of Na, is not relevant, which indicates that, when using this mycotoxin deactivator, milk contaminated with ATM1 can be further used.

Structural characterization of a homopolysaccharide produced by Weissella cibaria FMy 2-21-1 and its potential application as a green corrosion inhibiting film

Steel corrosion is a global issue that affects safety and the economy. Currently, the homopolysaccharide (HoPS) structure of a novel lactic acid bacterium (LAB) is under study, as well as its application as a green corrosion inhibitor. Weissella cibaria FMy 2-21-1 is a LAB strain capable of producing HoPS in sucrose enriched media. The isolated and purified HoPS was characterized by different spectroscopic analyses as a linear α-1,6 dextran adopting a random coil conformation, with high molecular weight and extended size in water. The polysaccharide showed a semi-crystalline organization, which is a requirement for film formation. Its biocoating showed a grainy network structure, with a slightly lesser hydrophobic role in the aqueous environment than in the ionic one. The electrochemical measurements of the steel-HoPS coating showed that the biopolymer layer acts as an anodic-type corrosion inhibitor, with high resistance to corrosion by water and with chloride ions which prevent pitting, a corrosion process typical of bare steel. Few reports have cited the application of LAB HoPS as corrosive coating inhibitors. This work is the first to explore the influence of a structurally characterized dextran from Weissella cibaria strain as a potential steel corrosion inhibitor in ionic environments.

Adsorption and enrichment of U in a cellulase-producing Trichoderma sp. and its physiological response mechanism

The cellulase produced by Trichoderma sp. was characterized by investigating the adsorption and enrichment of U and the physiological response to U exposure. The effects of U exposure (0 and 400 μM) on the growth, morphological characteristics, cellulase production, U adsorption, and U enrichment capacity of the Trichoderma strain were assessed. The effects of U exposure on the basic metabolism of this fungus were also analyzed by non-targeted metabolomics. Exposure to U (400 μM) for 24 h resulted in OD₆₀₀ turbidity of 0.278, and activities of carboxymethyl cellulase (CMC), filter paper enzyme (FPA), and β-glucosidase of 12834 U·mL^-1, 9285 U·mL^-1, and 12574 U·mL^-1, respectively. The measurement of the background α and β radioactivity showed an α activity concentration of 3.35 × 10⁶ Bq·kg^-1 in the fungus, a β activity concentration of 6.28 × 10⁵ Bq·kg^-1, and a U enrichment rate of 70.4 ± 4.5%. GC-MS metabolomics analysis identified a total of 319 metabolites (34 up-regulated and 30 down-regulated), which mainly caused the metabolic imbalance of organic acids and derivatives. The alanine, aspartate, and glutamate metabolic pathways were the most significantly enriched. Trichoderma sp. therefore has a strong ability to tolerate/accumulate U and continues to produce cellulase under U (400 μM) exposure. However, U interferes with the basic metabolism of this fungus.

Restoration of heavy metal-contaminated soil and water through biosorbents: A review of current understanding and future challenges

Heavy metal pollution in soil and water is a potential threat to human health as it renders food quality substandard. Different biosorbents such as microbial and agricultural biomass have been exploited for heavy metal immobilization in soil and sorptive removal in waters. Biosorption is an effective and sustainable method for heavy metal removal in soil and water, but the inherent challenges are to find cheap, selective, robust, and cost-effective bioadsorbents. Microbial and agricultural biomass and their modified forms such as nanocomposites and carbonaceous materials (viz., biochar, nanobiochar, biocarbon), might be useful for sequestration of heavy metals in soil via adsorption, ion exchange, complexation, precipitation, and enzymatic transformation mechanisms. In this review, potential biosorbents and their metal removal capacity in soil and water are discussed. The microbial adsorbents and modified composites of agricultural biomasses show improved performance, stability, reusability, and effectively immobilize heavy metals from soil and water. In the future, researchers may consider the modified composites, encapsulated biosorbents for soil and water remediation.

A comprehensive review on α-D-Glucans: Structural and functional diversity, derivatization and bioapplications

Glucans are the most abundant natural polysaccharides across the living kingdom with tremendous biological activities. Now a days, α-D-glucans are gaining importance as a prebiotics, nutraceuticals, immunostimulants, antiproliferative agents and biodegradable polymers in pharmaceutical and cosmetic sectors. A wide variety of bioresources including bacteria, fungi, lichens, algae, plants and animals produce α-D-glucans either as an exopolysaccharide (EPS) or a cell wall component or an energy storage polymer. The α-D-glucans exhibit great structural and functional diversity as the type of linkage and percentage of branching dictate the functional properties of glucans. Among the different linkages, bioactivities are greatly confined to the α-D-(1 → 3) linkages whereas starch and other polymers consisting of α-D-(1 → 4) (1 → 6) linkages are specific for food and pharmaceutical applications. However, the bioactivities of the α-D-(1 → 3) glucans in native form is limited mainly due to their hydrophobic nature. Hence several derivatization techniques have been developed to improve the bioavailability as well as bioactive features such as antiviral, antimicrobial, anti-inflammatory, antioxidant, immunomodulatory and antitumor properties. Though, several reports have presented about α-D-glucans, still there is an ambiguity in terms of their structure among different natural sources and moreover no comprehensive information was available on their derivatization techniques and application potential. Therefore, the present review summarizes distinct description on diverse sources, type of linkages, derivatization techniques as well as the application potential of the native and modified α-D-glucans.

Exploring potential impact(s) of cerium in mining wastewater on the performance of partial-nitrification process and nitrogen conversion microflora

Cerium Ce(III) is one of the major pollutants contained in wastewater generated during Ce(III) mining. However, the effect(s) of Ce(III) on the functional genera responsible for removing nitrogen biologically from wastewater has not been studied and reported. In this study, the effects of Ce(III) on aspects of partial-nitritation-(PN) process including ammonia oxidation rate (AOR), process kinetics, and microbial activities were investigated. It was found that the effect of dosing Ce(III) in the PN system correlated strongly with the AOR. Compared to the control, batch assays dosed with 5 mg/L Ce(III) showed elevated PN efficiency of about 121%, an indication that maximum biological response was feasible upon Ce(III) dose. It was also found that, PN performance was not adversely affected, given that Ce(III) dose was ≤20 mg/L. Process kinetics investigated also suggested that the maximum Ce(III) dose without any visible inhibition to the activities of ammonium oxidizing bacteria was 1.37 mg/L, but demonstrated otherwise when Ce(III) dose exceeded 5.63 mg/L. Compared to the control, microbes conducted efficient Ce(III) removal (averaged 98.66%) via biosorption using extracellular polymeric substances (EPS). Notably, significant deposits of Ce(III) was found within the EPS produced as revealed by SEM, EDX, CLSM and FTIR. 2-dimensional correlation infrared-(2DCOS-IR) revealed ester group (uronic acid) as a major organic functional group that promoted Ce(III) removal. Excitation-emission matrix-(EEM) spectrum and 2DCOS-IR suggested the dominance of Fulvic acid, hypothesized to have promoted the performance of the PN process under Ce(III) dosage.

The mechanisms of hyphal pellet formation mediated by polysaccharides, α-1,3-glucan and galactosaminogalactan, in Aspergillus species

Filamentous fungi are widely used for production of enzymes and chemicals, and are industrially cultivated both in liquid and solid cultures. Submerged culture is often used as liquid culture for filamentous fungi. In submerged culture, filamentous fungi show diverse macromorphology such as hyphal pellets and dispersed hyphae depending on culture conditions and genetic backgrounds of fungal strains. Although the macromorphology greatly affects the productivity of submerged cultures, the specific cellular components needed for hyphal aggregation after conidial germination have not been characterized. Recently we reported that the primary cell wall polysaccharide α-1,3-glucan and the extracellular polysaccharide galactosaminogalactan (GAG) contribute to hyphal aggregation in Aspergillus oryzae, and that a strain deficient in both α-1,3-glucan and GAG shows dispersed hyphae in liquid culture. In this review, we summarize our current understanding of the contribution of chemical properties of α-1,3-glucan and GAG to hyphal aggregation. Various ascomycetes and basidiomycetes have α-1,3-glucan synthase gene(s). In addition, some Pezizomycotina fungi, including species used in the fermentation industry, also have GAG biosynthetic genes. We also review here the known mechanisms of biosynthesis of α-1,3-glucan and GAG. Regulation of the biosynthesis of the two polysaccharides could be a potential way of controlling formation of hyphal pellets.

Effects of heavy rare earth element (yttrium) on partial-nitritation process, bacterial activity and structure of responsible microbial communities

Yttrium (Y(III)) is mined commercially for industrial purposes due to its excellent physical properties. However, the effects of Y(III) in mining-wastewater on the performance of partial-nitritation process and ammonia-oxidizing bacteria (AOB) have not been explored. To elucidate Y(III) effects on biological mechanisms, kinetics was conducted to establish a correlation between Y(III) dosage and specific-oxygen-uptake-rate (SOUR). The mechanism(s) demonstrated by bacterial population to resist against toxic effects from Y(III) dose was also investigated using scanning electron microscopy-(SEM), energy-dispersive X-ray spectroscopy-(EDS), confocal laser scanning microscopy-(CLSM)，Fourier transform infrared-(FTIR) spectroscopy, and 2-dimensional correlation infrared-(2DCOS-IR) approach. The study revealed a strong correlation between ammonium oxidation rate (AOR) and Y(III) dosage. AOR promotion was more pronounced when Y(III) concentration was ≤20 mg/L (maximum AOR of 12.39 mgN/L/h, at 5 mg/L), whereas inhibition when Y(III) in influent was >20 mg/L (minimum AOR of 7.34 mgN/L/h, at 500 mg/L). Aiba model demonstrated high-performance (R² = 0.962) when Y(III) concentration ranged 0-20 mg/L, whereas linear model fitted well (R² of 0.984) to experimental data when Y(III) dose ranged 20-500 mg/L. The maximum change in SOUR (Vmax), half-rate constant (Km), and inhibition constant (Ki) reached 1.04 d^-1, 20.12 mg/L, and 4.87 mg/L, respectively, an indication that dosage of Y(III) could affect the partial-nitritation process. SEM-EDS showed that the content of extracellular polymeric substances (EPS) increased along with increasing Y(III) dosage. When 20 mg/L of Y(III) was dosed, the fraction of Y(III) within the surface elemental composition of the sludge increased gradually whereas that of calcium decreased. To further comprehend the EPS production, CLSM results further revealed β-polysaccharide as the dominant component in the EPS. FTIR/2DCOD-IR showed that the chelation of polyguluronic sections within β-polysaccharide, together with hydrazine might be the main pathways of cell resistance, but β- glucan, may have caused the hormesis.

A Report on Fungal (1→3)-α-d-glucans: Properties, Functions and Application

The cell walls of fungi are composed of glycoproteins, chitin, and α- and β-glucans. Although there are many reports on β-glucans, α-glucan polysaccharides are not yet fully understood. This review characterizes the physicochemical properties and functions of (1→3)-α-d-glucans. Particular attention has been paid to practical application and the effect of glucans in various respects, taking into account unfavourable effects and potential use. The role of α-glucans in plant infection has been proven, and collected facts have confirmed the characteristics of Aspergillus fumigatus infection associated with the presence of glucan in fungal cell wall. Like β-glucans, there are now evidence that α-glucans can also stimulate the immune system. Moreover, α-d-glucans have the ability to induce mutanases and can thus decompose plaque.