Review of Levan polysaccharide: From a century of past experiences to future prospects

Expanding the horizons of levan: from microbial biosynthesis to applications and advanced detection methods

Levan, a β-(2,6)-linked fructose polymer, exhibits diverse properties that impart versatility, rendering it a highly sought-after biopolymer with various industrial applications. Levan can be produced by various microorganisms using sucrose, food industry byproducts and agricultural wastes. Microbial levan represents the most potent cost-effective process for commercial-scale levan production. This study reviews the optimization of levan production by understanding its biosynthesis, physicochemical properties and the fermentation process. In addition, genetic and protein engineering for its increased production and emerging methods for its detection are introduced and discussed. All of these comprehensive studies could serve as powerful tools to optimize levan production and broaden its applications across various industries.

Comprehensive rheological analysis of structurally related acetan-like heteroexopolysaccharides from two Kozakia baliensis strains in surfactants and galactomannan blends

Natural biopolymers become increasingly attractive as bio-based alternatives to petrol-based rheological modifiers, especially in personal care applications. However, many polysaccharides exhibit undesired properties in cosmetic applications such as limited viscosifying characteristics, unpleasant sensory properties, or incompatibility with certain formulation compounds. Here, a comprehensive rheological analysis of non-decorated acetan-like heteroexopolysaccharides derived from two Kozakia baliensis strains was performed in selected surfactant formulations. The results were compared to native xanthan gum and a genetically engineered xanthan variant, Xan∆gumFGL, which lacks any acetyl- and pyruvyl moieties and whose rheological properties are unaffected by saline environments. All four polysaccharides displayed a highly similar rheological performance in the non-ionic surfactant lauryl glucoside, while the rheological properties differed in amphoteric and anionic surfactants cocamidopropyl betaine and sodium laureth sulfate due to minor changes in side chain composition. Polysaccharide precipitation was observed in the presence of the cationic surfactant. Nevertheless, the native heteroexopolysaccharide derived from K. baliensis LMG 27018 shows significant potential as a salt-independent rheological modifier compared to the genetically engineered Xan∆gumFGL variant. In addition, blends of heteroexopolysaccharides from K. baliensis and several galactomannans displayed synergistic effects which were comparable to native xanthan gum-galactomannan blends. This study shows that heteroexopolysaccharides of K. baliensis are capable of further extending the portfolio of bio-based rheological modifiers.

Effect of Tight Junction-Modulating FCIGRL-Modified Peptides on the Intestinal Absorption of Doxorubicin in Rats

Doxorubicin is a potent chemotherapy drug, but its oral bioavailability is limited due to its low membrane permeability. Thus, absorption enhancers such as zonula occludens toxin and its six-mer fragment, FCIGRL, have been studied to address this issue. This study aimed to evaluate the effectiveness of four peptides (Pep1, Pep2, Pep3, and Pep4) derived from FCIGRL and investigate the changes in the absorption of doxorubicin, to propose an absorption enhancer for doxorubicin. Pep1 is a modified version of FCIGRL in which the hydroxyl group at the C-terminus is replaced with an amino group. Pep2 is a modified Pep1 in which cysteine is replaced with N3-substituted dipropionic acid. Pep3 and Pep4 are Pep2-modified homodimers. Pharmacokinetic analysis was performed in rats after the intraduodenal administration of doxorubicin solutions containing each FCIGRL-modified peptide and the stabilizer levan or benzalkonium chloride (BC). The results showed that Pep3 and Pep4 administered with levan each significantly increased the intestinal absorption of doxorubicin, as did Pep2 administered with levan/BC. In particular, 10 mg·kg-1 of Pep4 with levan significantly increased the area under the curve (AUC)0-240min of doxorubicin by 2.38-fold (p < 0.01) and the peak concentration (Cmax) by 3.30-fold (p < 0.01) compared to the control solution. The study findings indicate that Pep2, Pep3, and primarily Pep4 are novel absorption enhancers that can open tight junctions for doxorubicin, and the effectiveness of the peptides was directly affected by the presence of levan or levan/BC.

Effect of levan polysaccharide on chronological aging in the yeast Saccharomyces cerevisiae

Levan is a fructose-based biopolymer with diverse applications in the medicinal, pharmaceutical, and food industries. However, despite its extensive biological and pharmacological actions, including antioxidant, anti-inflammatory, and antidiabetic properties, research on its anti-aging potential is limited. This study explored levan's impact on the chronological lifespan (CLS) of yeast Saccharomyces cerevisiae for the first time. The results show that levan treatment significantly extended the CLS of wild-type (WT) yeast by preventing the accumulation of oxidative stress markers (reactive oxygen species, malondialdehyde, and protein carbonyl content) and ameliorating apoptotic features such as reduced mitochondrial membrane potential, loss of plasma membrane integrity, and externalization of phosphatidylserine. By day 40 of the CLS, a significant increase in yeast viability of 6.8 % (p < 0.01), 11.9 % (p < 0.01), and 20.8 % (p < 0.01) was observed at 0.25, 0.5, and 1 mg/mL of levan concentrations, respectively, compared to control (0 %). This study's results indicate that levan treatment substantially modulates the expression of genes involved in the TORC1/Sch9 pathway. Moreover, levan treatment significantly extended the CLS of yeast antioxidant-deficient mutant sod2Δ and antiapoptotic gene-deficient mutant pep4Δ. Levan also extended the CLS of signaling pathway gene-deficient mutants such as pkh2Δ, rim15Δ, atg1, and ras2Δ, while not affecting the CLS of tor1Δ and sch9Δ.

Design and Development of Transient Sensing Devices for Healthcare Applications

With the ever-growing requirements in the healthcare sector aimed at personalized diagnostics and treatment, continuous and real-time monitoring of relevant parameters is gaining significant traction. In many applications, health status monitoring may be carried out by dedicated wearable or implantable sensing devices only within a defined period and followed by sensor removal without additional risks for the patient. At the same time, disposal of the increasing number of conventional portable electronic devices with short life cycles raises serious environmental concerns due to the dangerous accumulation of electronic and chemical waste. An attractive solution to address these complex and contradictory demands is offered by biodegradable sensing devices. Such devices may be able to perform required tests within a programmed period and then disappear by safe resorption in the body or harmless degradation in the environment. This work critically assesses the design and development concepts related to biodegradable and bioresorbable sensors for healthcare applications. Different aspects are comprehensively addressed, from fundamental material properties and sensing principles to application-tailored designs, fabrication techniques, and device implementations. The emerging approaches spanning the last 5 years are emphasized and a broad insight into the most important challenges and future perspectives of biodegradable sensors in healthcare are provided.

Electrosprayable Levan-Coated Nanoclusters and Ultrasound-Responsive Drug Delivery for Cancer Therapy

In this study, we synthesized levan shell hydrophobic silica nanoclusters encapsulating doxorubicin (L-HSi-Dox) and evaluated their potential as ultrasound-responsive drug delivery systems for cancer treatment. L-HSi-Dox nanoclusters were successfully fabricated by integrating a hydrophobic silica nanoparticle-doxorubicin complex as the core and an amphiphilic levan carbohydrate polymer as the shell by using an electrospray technique. Characterization analyses confirmed the stability, size, and composition of the nanoclusters. In particular, the nanoclusters exhibited a controlled release of Dox under aqueous conditions, demonstrating their potential as efficient drug carriers. The levanic groups of the nanoclusters enhanced the targeted delivery of Dox to specific cancer cells. Furthermore, the synergism between the nanoclusters and ultrasound effectively reduced cell viability and induced cell death, particularly in the GLUT5-overexpressing MDA-MB-231 cells. In a tumor xenograft mouse model, treatment with the nanoclusters and ultrasound significantly reduced the tumor volume and weight without affecting the body weight. Collectively, these results highlight the potential of the L-HSi-Dox nanoclusters and ultrasound as promising drug delivery systems with an enhanced therapeutic efficacy for biomedical applications.

Sustainable production of heavy metal-binding levan by a subarctic permafrost thaw lake Pseudomonas strain 2ASCA

Pseudomonas strain 2ASCA isolated in subarctic Québec, Canada, produced a cell membrane bound levan-type exopolymer (yield 1.17 g/L), after incubation in growth media containing 6 % sucrose (w/v) at temperature of 15 °C for 96 h. The objective of this study was to optimize levan production by varying the growth parameters. Moreover, the polymer's chemical characterization has been studied with the aim of increasing knowledge and leading to future applications in many fields, including heavy metal remediation. Higher levan yields (7.37 g/L) were reached by setting up microbial fermentation conditions based on the re-use of the molasses obtained from sugar beet processing. Spectroscopy analyses confirmed the levan-type nature of the exopolymer released by strain 2ASCA, consisting of a β-(2,6)-linked fructose repeating unit. Gel permeation chromatography revealed that the polymer has a molecular weight of 13 MDa. Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) showed that the levan sequestered with a strong affinity Cr(III), which has never been previously reported, highlighting an interesting biosorption potential. In addition, SEM analysis revealed the formation of nanoparticles in acidified water solution.

Metabolome and transcriptome analyses reveal changes of rapeseed in response to ABA signal during early seedling development

Seed germination is an important development process in plant growth. The phytohormone abscisic acid (ABA) plays a critical role during seed germination. However, the mechanism of rapeseed in response to ABA is still elusive. In order to understand changes of rapeseed under exogenous ABA treatment, we explored differentially expressed metabolites (DEMs) and the differentially expressed genes (DEGs) between mock- and ABA-treated seedlings. A widely targeted LC-MS/MS based metabolomics were used to identify and quantify metabolic changes in response to ABA during seed germination, and a total of 186 significantly DEMs were identified. There are many compounds which are involved in ABA stimuli, especially some specific ABA transportation-related metabolites such as starches and lipids were screened out. Meanwhile, a total of 4440 significantly DEGs were identified by transcriptomic analyses. There was a significant enrichment of DEGs related to phenylpropanoid and cell wall organization. It suggests that exogenous ABA mainly affects seed germination by regulating cell wall loosening. Finally, the correlation analysis of the key DEMs and DEGs indicates that many DEGs play a direct or indirect regulatory role in DEMs metabolism. The integrative analysis between DEGs and DEMs suggests that the starch and sucrose pathways were the key pathway in ABA responses. The two metabolites from starch and sucrose pathways, levan and cellobiose, both were found significantly down-regulated in ABA-treated seedlings. These comprehensive metabolic and transcript analyses provide useful information for the subsequent post-transcriptional modification and post germination growth of rapeseed in response to ABA signals and stresses.

Insights in inulin binding and inulin oligosaccharide formation by novel multi domain endo-inulinases from Botrytis cinerea

World-wide, pathogenic fungi such as Botrytis cinerea cause tremendous yield losses in terms of food production and post-harvest food decay. Many fungi produce inulin-type oligosaccharides (IOSs) from inulin through endo-inulinases which typically show a two domain structure. B.cinerea lacks a two domain endo-inulinase but contains a three domain structure instead. Genome mining revealed three and four domain (d4) enzymes in the fungal kingdom. Here, three and two domain enzymes were compared in their capacity to produce IOSs from inulin. Hill kinetics were observed in three domain enzymes as compared to Michaelis-Menten kinetics in two domain enzymes, suggesting that the N-terminal extension functions as a carbohydrate binding module. Analysis of the IOS product profiles generated from purified GF6, GF12, GF16 and GF18 inulins and extensive sugar docking approaches led to enhanced insights in the active site functioning, revealing subtle differences between the endo-inulinases from Aspergillus niger and B. cinerea. Improved insights in structure-function relationships in fungal endo-inulinases offer opportunities to develop superior enzymes for the production of specific IOS formulations to improve plant and animal health (priming agents, prebiotics).

Generation and characterization of two new monoclonal antibodies produced by immunizing mice with plant fructans: New tools for immunolocalization of β-(2 → 1) and β-(2 → 6) fructans

Fructans are water-soluble polymers of fructose in which fructose units are linked by β-(2 → 1) and/or β-(2 → 6) linkages. In plants, they are synthesized in the vacuole but have also been reported in the apoplastic sap under abiotic stress suggesting that they are involved in plasmalemma protection and in plant-microbial interactions. However, the lack of fructan-specific antibodies currently prevents further study of their role and the associated mechanisms of action, which could be elucidated thanks to their immunolocalization. We report the production of two monoclonal antibodies (named BTM9H2 and BTM15A6) using mice immunization with antigenic compounds prepared from a mixture of plant inulins and levans conjugated to serum albumin. Their specificity towards fructans with β-(2 → 1) and/or β-(2 → 6) linkage has been demonstrated by immuno-dot blot tests on a wide range of carbohydrates. The two mAbs were used for immunocytolocalization of fructans by epifluorescence microscopy in various plant species. Fructan epitopes were specifically detected in fructan-accumulating plants, inside cells as well as on the surface of root tips, confirming both extracellular and intracellular localizations. The two mAbs provide new tools to identify the mechanism of extracellular fructan secretion and explore the roles of fructans in stress resistance and plant-microorganism interactions.

Levan Production by Suhomyces kilbournensis Using Sugarcane Molasses as a Carbon Source in Submerged Fermentation

The valorization of byproducts from the sugarcane industry represents a potential alternative method with a low energy cost for the production of metabolites that are of commercial and industrial interest. The production of exopolysaccharides (EPSs) was carried out using the yeast Suhomyces kilbournensis isolated from agro-industrial sugarcane, and the products and byproducts of this agro-industrial sugarcane were used as carbon sources for their recovery. The effect of pH, temperature, and carbon and nitrogen sources and their concentration in EPS production by submerged fermentation (SmF) was studied in 170 mL glass containers of uniform geometry at 30 °C with an initial pH of 6.5. The resulting EPSs were characterized with Fourier-transform infrared spectroscopy (FT-IR). The results showed that the highest EPS production yields were 4.26 and 44.33 g/L after 6 h of fermentation using sucrose and molasses as carbon sources, respectively. Finally, an FT-IR analysis of the EPSs produced by S. kilbournensis corresponded to levan, corroborating its origin. It is important to mention that this is the first work that reports the production of levan using this yeast. This is relevant because, currently, most studies are focused on the use of recombinant and genetically modified microorganisms; in this scenario, Suhomyces kilbournensis is a native yeast isolated from the sugar production process, giving it a great advantage in the incorporation of carbon sources into their metabolic processes in order to produce levan sucrose, which uses fructose to polymerize levan.

Exploration of the Native Sucrose Operon Enables the Development of an Inducible T7 Expression System in Paenibacillus polymyxa

The use of Paenibacillus polymyxa as an industrial producer is limited by the lack of suitable synthetic biology tools. In this study, we identified a native sucrose operon in P. polymyxa. Its structural and functional relationship analysis revealed the presence of multiple regulatory elements, including four ScrR-binding sites and a catabolite-responsive element (CRE). In P. polymyxa, we established a cascade T7 expression system involving an integrated T7 RNA polymerase (T7P) regulated by the sucrose operon and a T7 promoter. It enables controllable gene expression by sucrose and regulatory elements, and a 5-fold increase in expression efficiency compared with the original sucrose operon was achieved. Further deletion of SacB in P. polymyxa resulted in a 38.95% increase in the level of thermophilic lipase (TrLip) production using the cascade T7 induction system. The results highlight the effectiveness of sucrose regulation as a novel synthetic biology tool, which facilitates exploring gene circuits and enables their dynamic regulation.

Targeting the Bottlenecks in Levan Biosynthesis Pathway in Bacillus subtilis and Strain Optimization by Computational Modeling and Omics Integration

Levan is a fructan polymer with many industrial applications such as the formulation of hydrogels, drug delivery, and wound healing, among others. To this end, metabolic systems engineering is a valuable method to improve the yield of a specific metabolite in a wide range of bacterial and eukaryotic organisms. In this study, we report a systems biology approach integrating genomics data for the Bacillus subtilis model, wherein the metabolic pathway for levan biosynthesis is unpacked. We analyzed a revised genome-scale enzyme-constrained metabolic model (ecGEM) and performed simulations to increase levan biopolymer production capacity in B. subtilis. We used the model ec_iYO844_lvn to (1) identify the essential genes and bottlenecks in levan production, and (2) specifically design an engineered B. subtilis strain capable of producing higher levan yields. The FBA and FVA analysis showed the maximal growth rate of the organism up to 0.624 hr-1 at 20 mmol gDw-1 hr-1 of sucrose intake. Gene knockout analyses were performed to identify gene knockout targets to increase the levan flux in B. subtilis. Importantly, we found that the pgk and ctaD genes are the two target genes for the knockout. The perturbation of these two genes has flux gains for levan production reactions with 1.3- and 1.4-fold the relative flux span in the mutant strains, respectively, compared to the wild type. In all, this work identifies the bottlenecks in the production of levan and possible ways to overcome them. Our results provide deeper insights on the bacterium's physiology and new avenues for strain engineering.

Exopolysaccharide β-(2,6)-levan-type fructans have a molecular-weight-dependent modulatory effect on Toll-like receptor signalling

SCOPE

Fructans are a group of dietary fibers which are known to have many beneficial effects including immune-modulating effects. A family of fructans are β-(2,6)-linked levan-type fructans that are known to serve as exopolysaccharides in the cell wall of many species of bacteria including commensal bacteria and probiotics. It is still largely unknown whether and how they can serve as immunomodulating molecules.

RESULTS

Microbial β-(2,6)-fructans were found to induce TLR-dependent activation of THP-1 cells, in a dose-dependent fashion. Low molecular weight (Mw), medium Mw and high Mw β-(2,6)-fructans activated both TLR2 and 4 in a dose- and molecular weight-dependent fashion. In addition, it was found that β-(2,6)-fructans were able to inhibit signalling of various TLRs with the strongest effect on TLR5 and 8, which were inhibited by all the β-(2,6)-fructans in a dose- and molecular weight-dependent fashion. The final effect of this activation and inhibition of TLRs on cytokine responses in human dendritic cells (DCs) was minor which may be explained by the counter-activating effects of the different β-(2,6)-linked levan-type fructans on inhibition of TLR signalling in the DCs.

CONCLUSION

A mechanism by which exopolysaccharide levan β-(2,6)-fructans can be immune-modulating is by impacting TLR signalling. This knowledge could lead to food in which exopolysaccharide levan β-(2,6)-fructans are added for preventing disorders where TLR-signalling is modulated.

Characterization of Levan Fructan Produced by a Gluconobacter japonicus Strain Isolated from a Sugarcane Processing Facility

During raw sugarcane processing, a significant portion of lost sucrose is attributable to microbial degradation. Sucrose consumption by many bacteria is also linked to the production of exopolysaccharides (EPS) such as dextrans and fructans. These resulting EPS cause operational challenges during raw sugar manufacturing. Here, we report the characterization of EPS from a fructan-forming Gluconobacter japonicus bacterium that we previously isolated from a Louisiana sugarcane factory. The genome sequencing revealed the presence of two encoded levansucrase genes, lsrA and lsrB. One levansucrase, LsrB, was detected in the secreted protein fraction of G. japonicus LASM12 by QTOF LC-MS. The spotting assays indicated that G. japonicus produces EPS using sucrose and raffinose as substrates. The G. japonicus EPS correlated with levan fructan commercial standards by 1H-NMR, and with the characteristic carbohydrate fingerprint region for FTIR spectra, confirming that the G. japonicus EPS is levan fructan. The glycosyl composition and glycosyl linkage analysis revealed a linear β-2,6-fructofuranosyl polysaccharide with occasional (5.7%) β-2,1-fructofuranosyl branches. The gel permeation chromatography of the levan fructan EPS showed two main peaks at 4.5 kDa and 8 kDa and a very minor peak at 500 kDa. G. japonicus was identified as a producer of levan fructan. These findings will be useful for future studies aimed at evaluating the impact of levan fructans on sugar crop processing, which have been historically underestimated in industry.

Characterization of levans produced by levansucrases from Bacillus amyloliquefaciens and Gluconobacter oxydans: Structural, techno-functional, and anti-inflammatory properties

Levans of different structures and molecular weights (MW) can display various techno-functional and health-promoting properties. In the present study, selected levans were produced by the transfructosylation of sucrose catalyzed by levansucrases from Bacillus amyloliquefaciens and Gluconobacter oxydans, and their structural, techno-functional and anti-inflammatory properties were investigated. NMR and methylation/GC analysis confirmed the structure of β-(2, 6) levans. The structural characterization led to the classification of levans as high MW (HMW, ≥100 kDa), low MW (LMW, ≤20 kDa) and mix L/HMW ones. Levan with higher MW had more linear fructosyl units with fewer reducing ends and branching residues. LMW levan showed the highest foaming capacity and stability while HMW levan had the highest emulsion stability. HMW and mix L/HMW levans showed comparable water and oil-holding capacities, which were higher than LMW. HMW and mix L/HMW levans were found to have gelling properties at low concentrations. The rheological behaviour of HMW levan-based gel was a more viscous-like gel, while that of mix L/HMW levan-based one showed more elastic solid like-gel. The temperature also influenced the rheology of levan, showing that the mix L/HMW levan gel network was the most thermal stable as its viscoelasticity remained constant at the highest temperature (75 °C). Studies on the biological activity of levans of HMW and LMW revealed in-vitro anti-inflammatory properties as they significantly reduced the production of LPS-triggered pro-inflammatory cytokines in differentiated Caco-2 cells.

Insights into the heterogeneity of levan polymers synthesized by levansucrase Bs-SacB from Bacillus subtilis 168

Levan is an enzymatically synthesized fructose polymer with widely reported structural heterogeneity depending on the producing levansucrase, the reaction conditions employed for its synthesis and the characterization techniques. We studied here the specific properties of levan produced by recombinant levansucrase from B. subtilis 168 (Bs-SacB), often characterized as a bimodal distribution, that is, a mixture of low and high molecular weight levan. We found significant differences between both levans in terms of the already reported molecular weight, size and morphology using different analytical methods. The low molecular weight levan consists of a non-uniform polymer ranging from 50 to 230 kDa, synthesized through a non-processive mechanism that can spontaneously form spherical nanoparticles in the reaction medium. In contrast, high molecular weight levan is a uniform polymer, most probably synthesized through a processive mechanism, with an average molecular weight of 30,750 kDa and a poorly defined nano-structure. This is the first report exploring differences in morphology between low and high molecular weight levans. Our findings demonstrate that only the low molecular weight levan forms spherical nanoparticles in the reaction medium and that high molecular weight levan is mainly composed of a 33,000 kDa fraction with a microgel behavior.

Polyhydroxyalkanoates and exopolysaccharides: An alternative for valuation of the co-production of microbial biopolymers

Polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPSs) belong to a class of abundant biopolymers produced by various fermenting microorganisms. These biocompounds have high value-added potential and can be produced concurrently. Co-production of PHAs and EPSs is a strategy employed by researchers to reduce costs associated with large-scale production. EPSs and PHAs are non-toxic, biocompatible, and biodegradable, making them suitable for various industrial sectors, including packaging and the medical and pharmaceutical industries. These biopolymers can be derived from agro-industrial residues, thus contributing to the bioeconomy by producing high-value-added products. This review investigates approaches for simultaneously synthesizing PHAs and EPSs using different carbon sources and microorganisms.

First transcriptomic insight into the reprogramming of human macrophages by levan-type fructans

Based on stimuli in the biological milieu, macrophages can undergo classical activation into the M1 pro-inflammatory (anti-cancer) phenotype or to the alternatively activated M2 anti-inflammatory one. Drug-free biomaterials have emerged as a new therapeutic strategy to modulate macrophage phenotype. Among them, polysaccharides polarize macrophages to M1 or M2 phenotypes based on the surface receptors they bind. Levan, a fructan, has been proposed as a novel biomaterial though its interaction with macrophages has been scarcely explored. In this study, we investigate the interaction of non-hydrolyzed and hydrolyzed Halomonas levan and its sulfated derivative with human macrophages in vitro. Viability studies show that these levans are cell compatible. In addition, RNA-sequencing analysis reveals the upregulation of pro-inflammatory pathways. These results are in good agreement with real time-quantitative polymerase chain reaction that indicates higher expression levels of C-X-C Motif Chemokine Ligand 8 and interleukin-6 genes and the M2-to-M1 reprogramming of these cells upon levan treatment. Finally, cytokine release studies confirm that hydrolyzed levans increase the secretion of pro-inflammatory cytokines and reprogram IL-4-polarized macrophages to the M1 state. Overall findings indicate that Halomonas levans trigger a classical macrophage activation and pave the way for their application in therapeutic interventions requiring a pro-inflammatory phenotype.

Characterization, production optimization, and fructanogenic traits of levan in a new Microbacterium isolate

Levan is a high-valued β-(2,6)-linked fructan with promising physicochemical and physiological properties and has diverse potential applications in the food, nutraceutical, pharmaceutical and cosmetic industry, but its commercial availability is still restricted to the relatively high costs of production. In this study, a strain identified as Microbacterium sp. XL1 was isolated from soil and highly produced exopolysaccharide (EPS). HPLC, FTIR and NMR spectroscopy revealed XL1-EPS is a levan-type fructan connected by β-(2, 6) linkages. SEM, DLS and TGA-DSC analysis showed that XL1-EPS processed high morphological versatility, narrow size distribution in its solutions and excellent thermal stability. The levan yield reached 83.67 ± 4.06 g/L with corresponding productivity of 3.49 ± 0.17 g/L/h and a conversion yield of 39.8 ± 1.9 % using sucrose (210 g/L) as substrates under the optimal cultivation conditions concluded by the response surface methodology (RSM). More strikingly, the XL1 strain also has multi-type fructanases to generate levanbiose, kestose, DFA IV and other L-FOSs. These results suggest Microbacterium sp. XL1 is a promising strain to produce levan and can provide various levan/inulin-degrading enzymes to create a great diversity of FOSs.

Influence of pH on Inulin Conversion to 2,3-Butanediol by Bacillus licheniformis 24: A Gene Expression Assay

2,3-Butanediol (2,3-BD) is an alcohol highly demanded in the chemical, pharmaceutical, and food industries. Its microbial production, safe non-pathogenic producer strains, and suitable substrates have been avidly sought in recent years. The present study investigated 2,3-BD synthesis by the GRAS Bacillus licheniformis 24 using chicory inulin as a cheap and renewable substrate. The process appears to be pH-dependent. At pH 5.25, the synthesis of 2,3-BD was barely detectable due to the lack of inulin hydrolysis. At pH 6.25, 2,3-BD concentration reached 67.5 g/L with rapid hydrolysis of the substrate but was accompanied by exopolysaccharide (EPS) synthesis. Since inulin conversion by bacteria is a complex process and begins with its hydrolysis, the question of the acting enzymes arose. Genome mining revealed that several glycoside hydrolase (GH) enzymes from different CAZy families are involved. Five genes encoding such enzymes in B. licheniformis 24 were amplified and sequenced: sacA, sacB, sacC, levB, and fruA. Real-time RT-PCR experiments showed that the process of inulin hydrolysis is regulated at the level of gene expression, as four genes were significantly overexpressed at pH 6.25. In contrast, the expression of levB remained at the same level at the different pH values at all-time points. It was concluded that the sacC and sacA/fruA genes are crucial for inulin hydrolysis. They encode exoinulinase (EC 3.2.1.80) and sucrases (EC 3.2.1.26), respectively. The striking overexpression of sacB under these conditions led to increased synthesis of EPS; therefore, the simultaneous production of 2,3-BD and EPS cannot be avoided.

Strategy to combat biofilms: a focus on biofilm dispersal enzymes

Bacterial biofilms, which consist of three-dimensional extracellular polymeric substance (EPS), not only function as signaling networks, provide nutritional support, and facilitate surface adhesion, but also serve as a protective shield for the residing bacterial inhabitants against external stress, such as antibiotics, antimicrobials, and host immune responses. Biofilm-associated infections account for 65-80% of all human microbial infections that lead to serious mortality and morbidity. Tremendous effort has been spent to address the problem by developing biofilm-dispersing agents to discharge colonized microbial cells to a more vulnerable planktonic state. Here, we discuss the recent progress of enzymatic eradicating strategies against medical biofilms, with a focus on dispersal mechanisms. Particularly, we review three enzyme classes that have been extensively investigated, namely glycoside hydrolases, proteases, and deoxyribonucleases.

Characterization and alteration of product specificity of Beijerinckia indica subsp. indica β-fructosyltransferase

The trisaccharide 1-kestose, a major constituent of fructooligosaccharide, has strong prebiotic effects. We used high-performance liquid chromatography and 1H nuclear magnetic resonance spectroscopy to show that BiBftA, a β-fructosyltransferase belonging to glycoside hydrolase family 68, from Beijerinckia indica subsp. indica catalyzes transfructosylation of sucrose to produce mostly 1-kestose and levan polysaccharides. We substituted His395 and Phe473 in BiBftA with Arg and Tyr, respectively, and analyzed the reactions of the mutant enzymes with 180 g/L sucrose. The ratio of the molar concentrations of glucose and 1-kestose in the reaction mixture with wild-type BiBftA was 100:8.1, whereas that in the reaction mixture with the variant H395R/F473Y was 100:45.5, indicating that H395R/F473Y predominantly accumulated 1-kestose from sucrose. The X-ray crystal structure of H395R/F473Y suggests that its catalytic pocket is unfavorable for binding of sucrose while favorable for transfructosylation.

Synthesis and molecular characterization of levan produced by immobilized Microbacterium paraoxydans

In this study, we report high molecular weight (HMW) levan production by whole cells of Microbacterium paraoxydans, previously reported to be a good producer of fructooligosaccharides. Structural analysis of the extracellularly produced fructan indicated the glycosidic bonds between the adjacent fructose to be of β-(2, 6) linkage with over 90% of the fructan to have molecular weight around 2 × 108 Da and 10% with a molecular weight of ∼20 kDa. Immobilization of the cells in Ca-alginate led to the production of 44.6 g/L levan with a yield of 0.29 g/g sucrose consumed. Factors affecting the conversion rate were identified by One-Factor-At-a-Time (OFAT) analysis and the combination of these (initial sucrose concentration of 400 g/L, 100 mM buffer pH 7, the temperature of 37 °C and 20 mM CaCl2) led to the production of ∼129 g/L of levan with a yield of ∼0.41 g/g sucrose consumed and volumetric productivity of 1.8 g/L/h.

Understanding the effects of chitosan, chia mucilage, levan based composite coatings on the shelf life of sweet cherry

Sweet cherry (Prunus avium L.) fruits are prone to quality and quantity loss in shelf-life conditions and cold storage due to their short post-harvest life. Until now efforts have been made to extend the shelf life of the sweet cherry. However, an efficient and commercially scalable process remains elusive. To contribute to this challenge, here in this study, biobased composite coatings consisting of chitosan, mucilage, and levan, were applied on sweet cherry fruits and tested for postharvest parameters in both market and cold storage conditions. Results demonstrated that the shelf life of sweet cherries can be extended until the 30^th day while retaining important post-harvest properties like decreased weight loss, fungal deterioration, increased stem removal force, total flavonoid, l-ascorbic acid, and oxalic acid. Given the cost-effectiveness of the polymers used, the findings of this study indicate the feasibility of extending the shelf-life of sweet cherries on a larger scale.

Traversing the diverse avenues of exopolysaccharides-based nanocarriers in the management of cancer

Exopolysaccharides are unique polymers generated by living organisms such as algae, fungi and bacteria to protect them from environmental factors. After a fermentative process, these polymers are extracted from the medium culture. Exopolysaccharides have been explored for their anti-viral, anti-bacterial, anti-tumor, and immunomodulatory effects. Specifically, they have acquired massive attention in novel drug delivery strategies owing to their indispensable properties like biocompatibility, biodegradability, and lack of irritation. Exopolysaccharides such as dextran, alginate, hyaluronic acid, pullulan, xanthan gum, gellan gum, levan, curdlan, cellulose, chitosan, mauran, and schizophyllan exhibited excellent drug carrier properties. Specific exopolysaccharides, such as levan, chitosan, and curdlan, have demonstrated significant antitumor activity. Moreover, chitosan, hyaluronic acid and pullulan can be employed as targeting ligands decorated on nanoplatforms for effective active tumor targeting. This review shields light on the classification, unique characteristics, antitumor activities and nanocarrier properties of exopolysaccharides. In addition, in vitro human cell line experiments and preclinical studies associated with exopolysaccharide-based nanocarriers have also been highlighted.

Valorization of Using Agro-Wastes for Levan through Submerged Fermentation and Statistical Optimization of the Process Variables Applying Response Surface Methodology (RSM) Design

Levan is a homopolysaccharide of fructose units that repeat as its structural core. As an exopolysaccharide (EPS), it is produced by a great variety of microorganisms and a small number of plant species. The principal substrate used for levan production in industries, i.e., sucrose, is expensive and, hence, the manufacturing process requires an inexpensive substrate. As a result, the current research was designed to evaluate the potential of sucrose-rich fruit peels, i.e., mango peels, banana peels, apple peels, and sugarcane bagasse, to produce levan using Bacillus subtilis via submerged fermentation. After screening, the highest levan-producing substrate, mango peel, was used to optimize several process parameters (temperature, incubation time, pH, inoculum volume, and agitation speed) employing the central composite design (CCD) of response surface methodology (RSM), and their impact on levan production was assessed. After incubation for 64 h at 35 °C and pH 7.5, the addition of 2 mL of inoculum, and agitation at 180 rpm, the highest production of levan was 0.717 g/L of mango peel hydrolysate (obtained from 50 g of mango peels/liter of distilled water). The F-value of 50.53 and p-value 0.001 were calculated using the RSM statistical tool to verify that the planned model was highly significant. The selected model's accuracy was proven by a high value (98.92%) of the coefficient of determination (R²). The results obtained from ANOVA made it clear that the influence of agitation speed alone on levan biosynthesis was statistically significant (p-value = 0.0001). The functional groups of levan produced were identified using FTIR (Fourier-transform ionization radiation). The sugars present in the levan were measured using HPLC and the levan was found to contain only fructose. The average molecular weight of the levan was 7.6 × 10⁶ KDa. The findings revealed that levan can be efficiently produced by submerged fermentation using inexpensive substrate, i.e., fruit peels. Furthermore, these optimized cultural conditions can be applied on a commercial scale for industrial production and commercialization of levan.

Exopolysaccharides Producing Bacteria: A Review

Bacterial exopolysaccharides (EPS) are essential natural biopolymers used in different areas including biomedicine, food, cosmetic, petroleum, and pharmaceuticals and also in environmental remediation. The interest in them is primarily due to their unique structure and properties such as biocompatibility, biodegradability, higher purity, hydrophilic nature, anti-inflammatory, antioxidant, anti-cancer, antibacterial, and immune-modulating and prebiotic activities. The present review summarizes the current research progress on bacterial EPSs including their properties, biological functions, and promising applications in the various fields of science, industry, medicine, and technology, as well as characteristics and the isolation sources of EPSs-producing bacterial strains. This review provides an overview of the latest advances in the study of such important industrial exopolysaccharides as xanthan, bacterial cellulose, and levan. Finally, current study limitations and future directions are discussed.

Investigation of biocatalytic production of lactosucrose and fructooligosaccharides using levansucrases and dairy by-products as starting materials

Selected levansucrases (LSs) were investigated for their ability to catalyze the transfructosylation of lactose/sucrose into lactosucrose and fructooligosaccharides (FOSs). Additionally, dairy by-products, including whey permeate (WP) and milk permeate (MP), were assessed for their effectiveness as lactose sources. LSs from Gluconobacter oxydans (LS1), Vibrio natriegens (LS2), Novosphingobium aromaticivorans (LS3), and Burkholderia graminis (LS4) were utilized in three transfructosylation reactions that combined sucrose with either lactose, WP, or MP. All LSs demonstrated a higher transfructosylation activity than hydrolytic one, except for V. natriegens LS2 in the presence of sucrose and MP/sucrose. Furthermore, the bioconversion efficiency of lactose/sucrose into lactosucrose and FOSs exhibited varying time courses and end-product profiles. Both the acceptor specificity of LS and the thermodynamic equilibrium of its reaction modulated the end-product profile. V. natriegens LS2 resulted in the highest lactosucrose production of 328 and 251 g/L with lactose/sucrose and WP/sucrose, respectively. Our results revealed the potential of LS-catalyzed transfructosylation for the biocatalytic production of both lactosucrose and FOSs from abundant biomasses.

Outer membrane utilisomes mediate glycan uptake in gut Bacteroidetes

Bacteroidetes are abundant members of the human microbiota, utilizing a myriad of diet- and host-derived glycans in the distal gut¹. Glycan uptake across the bacterial outer membrane of these bacteria is mediated by SusCD protein complexes, comprising a membrane-embedded barrel and a lipoprotein lid, which is thought to open and close to facilitate substrate binding and transport. However, surface-exposed glycan-binding proteins and glycoside hydrolases also play critical roles in the capture, processing and transport of large glycan chains. The interactions between these components in the outer membrane are poorly understood, despite being crucial for nutrient acquisition by our colonic microbiota. Here we show that for both the levan and dextran utilization systems of Bacteroides thetaiotaomicron, the additional outer membrane components assemble on the core SusCD transporter, forming stable glycan-utilizing machines that we term utilisomes. Single-particle cryogenic electron microscopy structures in the absence and presence of substrate reveal concerted conformational changes that demonstrate the mechanism of substrate capture, and rationalize the role of each component in the utilisome.

Synthesis of octenyl succinic anhydride-modified levan and investigation of its microstructural, physicochemical, and emulsifying properties

In this study, levan from Bacillus licheniformis NS032 was modified in an aqueous medium by octenyl succinic anhydride (OSA), and the properties of the obtained derivatives were studied. The maximum efficiency in the synthesis reaction was achieved at 40 °C and a polysaccharide slurry concentration of 30 %. Increasing the reagent concentration (2-10 %) led to an increase in the degree of substitution (0.016-0.048). Structures of derivatives were confirmed by FTIR and NMR. Scanning electronic microscopy, thermogravimetry, and dynamic light scattering analyses showed that the derivatives with degrees of substitution of 0.025 and 0.036 retained levan's porous structure and thermostability and showed better colloidal stability than the native polysaccharide. The intrinsic viscosity of derivatives increased upon modification, while the surface tension of the 1 % solution was lowered to 61 mN/m. Oil-in-water emulsions prepared with sunflower oil (10 % and 20 %) by mechanical homogenization and 2 and 10 % derivatives in the continuous phase showed mean oil droplet sizes of 106-195 μm, while the distribution curves exhibited bimodal character. The studied derivatives have a good capacity to stabilize emulsions, as they have a creaming index ranging from 73 % to 94 %. The OSA-modified levans could have potential applications in new formulations of emulsion-based systems.

Recent Advances in the Polish Research on Polysaccharide-Based Nanoparticles in the Context of Various Administration Routes

Polysaccharides are the most abundant polymers in nature. They exhibit robust biocompatibility, reliable non-toxicity, and biodegradable character; thus, they are employed in multiple biomedical applications. The presence of chemically accessible functional groups on the backbone of biopolymers (amine, carboxyl, hydroxyl, etc.) makes them suitable materials for chemical modification or drug immobilisation. Among different drug delivery systems (DDSs), nanoparticles have been of great interest in scientific research in the last decades. In the following review, we want to address the issue of rational design of nanoparticle (NP)-based drug delivery systems in reference to the specificity of the medication administration route and resulting requirements. In the following sections, readers can find a comprehensive analysis of the articles published by authors with Polish affiliations in the last few years (2016-2023). The article emphasises NP administration routes and synthetic approaches, followed by in vitro and in vivo attempts toward pharmacokinetic (PK) studies. The 'Future Prospects' section was constructed to address the critical observations and gaps found in the screened studies, as well as to indicate good practices for polysaccharide-based nanoparticle preclinical evaluation.

Recent advances in natural small molecules as drug delivery systems

Drug delivery systems (DDSs) are a multidisciplinary approach toward the effective delivery of drugs to their target sites. Natural small molecule (NSM) compounds with anticancer activity, self-assembly and co-assembly functions show great potential for application as novel DDSs in the biomedical field. NSMs are widely sourced, have many modification sites, and readily form hydrogen bonds, π-π interactions, van der Waals interactions, and other non-covalent bonds in solvents, resulting in ordered structures. Moreover, their good biocompatibility and bioactivity allow compositions based on these compounds to be used in life science applications such as tissue engineering, drug delivery and cell imaging, showing the potential medical value of NSMs as DDSs. In this review, we summarise the role, assembly principles and applications of natural products such as triterpenoids, diterpenoids, sterols, alkaloids and polysaccharides in the construction of small molecule systems, which are expected to provide an important reference for the development of more active natural nanomaterials and the study of single or multi-component interactions.

Exploring the potential of Halomonas levan and its derivatives as active ingredients in cosmeceutical and skin regenerating formulations

Demand on natural products that contain biological ingredients mimicking growth factors and cytokines made natural polysaccharides popular in pharmaceutical and cosmetic industries. Levan is the β-(2-6) linked, nontoxic, biocompatible, water-soluble, film former fructan polymer that has diverse applications in pharmacy and cosmeceutical industries with its moisturizing, whitening, anti-irritant, anti-aging and slimming activities. Driven by the limited reports on few structurally similar levan polymers, this study presents the first systematic investigation on the effects of structurally different extremophilic Halomonas levan polysaccharides on human skin epidermis cells. In-vitro experiments with microbially produced linear Halomonas levan (HL), its hydrolyzed, (hHL) and sulfonated (ShHL) derivatives as well as enzymatically produced branched levan (EL) revealed increased keratinocyte and fibroblast proliferation (113-118 %), improved skin barrier function through induced expressions of involucrin (2.0 and 6.43 fold changes for HL and EL) and filaggrin (1.74 and 3.89 fold changes for hHL and ShHL) genes and increased type I collagen (2.63 for ShHL) and hyaluronan synthase 3 (1.41 for HL) gene expressions together with fast wound healing ability within 24 h (100 %, HL) on 2D wound models clearly showed that HL and its derivatives have high potential to be used as natural active ingredients in cosmeceutical and skin regenerating formulations.

New carbohydrate binding domains identified by phage display based functional metagenomic screens of human gut microbiota

Uncultured microbes represent a huge untapped biological resource of novel genes and gene products. Although recent genomic and metagenomic sequencing efforts have led to the identification of numerous genes that are homologous to existing annotated genes, there remains, yet, an enormous pool of unannotated genes that do not find significant sequence homology to existing annotated genes. Functional metagenomics offers a way to identify and annotate novel gene products. Here, we use functional metagenomics to mine novel carbohydrate binding domains that might aid human gut commensals in adherence, gut colonization, and metabolism of complex carbohydrates. We report the construction and functional screening of a metagenomic phage display library from healthy human fecal samples against dietary, microbial and host polysaccharides/glycoconjugates. We identify several protein sequences that do not find a hit to any known protein domain but are predicted to contain carbohydrate binding module-like folds. We heterologously express, purify and biochemically characterize some of these protein domains and demonstrate their carbohydrate-binding function. Our study reveals several previously unannotated carbohydrate-binding domains, including a levan binding domain and four complex N-glycan binding domains that might be useful for the labeling, visualization, and isolation of these glycans.

Acetobacteraceae as exopolysaccharide producers: Current state of knowledge and further perspectives

Exopolysaccharides formation against harmful biotic and abiotic environmental influences is common among bacteria. By using renewable resources as a substrate, exopolysaccharides represent a sustainable alternative to fossil-based polymers as rheological modifiers in food, cosmetics, and pharmaceutical applications. The family of Acetobacteraceae, traditionally associated with fermented food products, has demonstrated their ability to produce a wide range of structural and functional different polymers with interesting physicochemical properties. Several strains are well known for their production of homopolysaccharides of high industrial importance, such as levan and bacterial cellulose. Moreover, some Acetobacteraceae are able to form acetan-like heteropolysaccharides with a high structural resemblance to xanthan. This mini review summarizes the current knowledge and recent trends in both homo- and heteropolysaccharide production by Acetobacteraceae.

Progress and prospects of biopolymers production strategies

In recent decades, biopolymers have garnered significant attention owing to their aptitude as an environmentally approachable precursor for an extensive application. In addition, due to their alluring assets and widespread use, biopolymers have made significant strides in their production based on various sources and forms. This review focuses on the most recent improvements and breakthroughs that have been made in the manufacturing of biopolymers, via sections focusing the most frequented and preferred routes like micro-macro, algae apart from focusing on microbials routes with special attention to bacteria and the synthetic biology avenue of biopolymer production. For ensuring the continued growth of the global polymer industry, promising research trends must be pursued, as well as methods for overcoming obstacles that arise in exploiting the beneficial properties exhibited by a variety of biopolymers.

Identification of a Thermostable Levansucrase from Pseudomonas orientalis That Allows Unique Product Specificity at Different Temperatures

The biological production of levan by levansucrase (LS, EC 2.4.1.10) has aroused great interest in the past few years. Previously, we identified a thermostable levansucrase from Celerinatantimonas diazotrophica (Cedi-LS). A novel thermostable LS from Pseudomonas orientalis (Psor-LS) was successfully screened using the Cedi-LS template. The Psor-LS showed maximum activity at 65 °C, much higher than the other LSs. However, these two thermostable LSs showed significantly different product specificity. When the temperature was decreased from 65 to 35 °C, Cedi-LS tended to produce high-molecular-weight (HMW) levan. By contrast, Psor-LS prefers to generate fructooligosaccharides (FOSs, DP ≤ 16) rather than HMW levan under the same conditions. Notably, at 65 °C, Psor-LS would produce HMW levan with an average Mw of 1.4 × 106 Da, indicating that a high temperature might favor the accumulation of HMW levan. In summary, this study allows a thermostable LS suitable for HMW levan and levan-type FOSs production simultaneously.

Characterization of a processive inulosucrase from Lactobacillus mulieris for efficient biosynthesis of high-molecular-weight inulin

Inulin has been determined to have many exceptional properties and functions and has been used in the food and pharmaceutical fields. Recently, microbial high-molecular-weight inulin synthesized from sucrose by inulosucrase attracted much attention. In this study, a novel inulosucrase from Lactobacillus mulieris was constructed, overexpressed, purified, and identified. The recombinant enzyme displayed the maximum activity at pH 6.0 and 55 °C, and it exhibited high thermostability below 45 °C. After optimizing the production conditions, the conversion rate from 100 g/L sucrose to inulin reached 31 %, meanwhile, the maximum molecular weight of produced inulin reached 3.21 × 10⁶ g/mol. The truncated IS showed a "processive" transfructosylation process, only synthesizing a small number of short-chain oligosaccharides with polymerization degrees below 6, which was in favor of the accumulation of high-molecular-weight inulin. Given this, L. mulieris inulosucrase might be a good potential candidate for the industrial production of high-molecular-weight inulin.

Small molecules as cancer targeting ligands: Shifting the paradigm

Conventional chemotherapeutics exploration is hampered due to their nonspecific distribution leading to unintended serious toxicity. Toxicity is so severe that deciding to go for chemotherapy becomes a question of concern for many terminally ill cancer patients. However, with evolving times nanotechnology assisted in reducing the haywire distribution and channelizing the movement of drug-enclosing drug delivery systems to cancer cells to a greater extent, yet toxicity issues still could not be obliterated. Thus, active targeting appeared as a refuge, where ligands actively or specifically deliver linked chemotherapeutics and carriers to cancer cells. For a very long time, large molecule weight/macromolecular ligands (peptides and big polymers) were considered the first choice for ligand-directed active cancer targeting, due to their specificity towards overexpressed native cancer receptors. However, complex characterization, instability, and the expensive nature demanded to reconnoitre better alternatives for macromolecule ligands. The concept of small molecules as ligands emerged from the idea that few chemical molecules including chemotherapeutics have a higher affinity for cancer receptors, which are overexpressed on cell membranes, and may have the ability to assist in drug cellular uptake through endocytosis. But now the question is, can they assist the conjugated macro cargos to enter the cell or not? This present review will provide a holistic overview of the small molecule ligands explored till now.

Dual-functional carboxymethyl levan-based protein carrier for cosmeceutical application of human epidermal growth factor

Human epidermal growth factor (hEGF) has been a subject of extensive research as its wide range of physiological functions has many potential applications. However, due to the low stability of hEGF, its physiological effect is easily lost under conditions of use. To compensate for this, we developed a stable delivery system using levan-based nanoparticles. The entrapment yield of various tested proteins was significantly improved by employing carboxymethyl levan (CML) instead of levan; the entrapment yield of the CML-hEGF nanoparticles was 84.1 %. The size and zeta potential of the nanoparticles were identified as 199.9 ± 3.87 nm and -19.1 mV, respectively, using scanning electron microscopy (SEM) and particle size analysis. Dual biological functions of the nanoparticles (skin regeneration and moisturizing) were identified through collagen synthesis activity and aquaporin 3 expression level analysis. Stability of the prepared nanoparticles was also investigated via cell proliferation activity comparison under mimicked physiological conditions. The CML-hEGF nanoparticles maintained cell proliferation activity over 100 % for 6 weeks, while free hEGF was almost inactivated within 2 weeks. Taken together, our results indicate that the CML-based hEGF nanoparticles can be used in pharma- and cosmeceutical applications, guaranteeing a high entrapment capability, functionality, and stability.

Metabolomics Provides New Insights into Host Manipulation Strategies by Asobara japonica (Hymenoptera: Braconidae), a Fruit Fly Parasitoid

Asobara japonica (Hymenoptera: Braconidae) is an endoparasitoid wasp that can successfully parasitize a wide range of host species across the Drosophila genus, including the invasive crop pest Drosophila suzukii. Parasitoids are capable of regulating the host metabolism to produce the nutritional metabolites for the survival of their offspring. Here, we intend to investigate the metabolic changes in D. melanogaster hosts after parasitization by A. japonica, using the non-targeted LC-MS (liquid chromatography-mass spectrometry) metabolomics analysis. In total, 3043 metabolites were identified, most of which were not affected by A. japonica parasitization. About 205 metabolites were significantly affected in parasitized hosts in comparison to non-parasitized hosts. The changed metabolites were divided into 10 distinct biochemical groups. Among them, most of the lipid metabolic substances were significantly decreased in parasitized hosts. On the contrary, most of metabolites associated with the metabolism of amino acids and sugars showed a higher abundance of parasitized hosts, and were enriched for a wide range of pathways. In addition, eight neuromodulatory-related substances were upregulated in hosts post A. japonica parasitization. Our results reveal that the metabolites are greatly changed in parasitized hosts, which might help uncover the underlying mechanisms of host manipulation that will advance our understanding of host–parasitoid coevolution.

Co-production of levan with other high-value bioproducts: A review

Levan is a homopolysaccharide of fructose that has both scientific and industrial importance, with various applications in health, pharmaceutical, cosmetic and food industries. Despite its broad spectrum of uses, there are only a limited number of commercial levan sources due to the high costs related to its production. To make production economically viable, efforts have been concentrated on the selection of levan-producing microorganisms, the genetic manipulation of new strains, and the use of inexpensive agro-industrial byproducts as substrates. Another efficient strategy involves the concomitant synthesis of other products with high market value and as such, the successful co-production of levan was demonstrated with fructooligosaccharides, ethanol, sorbitol, poly-ε-lysine, poly-γ-glutamic acid and polyhydroxyalkanoates. This paper offers a systematic review of important aspects regarding recent strategies involving the simultaneous synthesis of levan and other bioproducts of aggregate value reported to date and discusses the challenges and opportunities for its large-scale production and applications.

Probiotic Properties of Exopolysaccharide-Producing Bacteria from Natto

Natto is a traditional Japanese food made from soybeans fermented with Bacillus subtilis var. natto. It is also a famous food in Thailand. Potential probiotics were screened from natto. Bacillus subtilis strain VN5 produced the most quantity of exopolysaccharide (EPS), so it was selected to study the properties of microbial EPS and probiotics. The Fourier transform infrared spectrometer or FT-IR spectroscopy confirmed the presence of carboxyl and hydroxyl groups. The patterns of FT-IR and levans are similar. The basic properties of probiotics were revealed. The 90% of VN5 strain resisted lysozyme within 30 min. VN5 survived under acidic conditions (pH 1-6), and the survival rate in 0.3%, 0.5%, and 1% bile solutions for 24 h was 100%. Unfortunately, VN5 did not inhibit the growth of Escherichia coli, Staphylococcus aureus, and Salmonella typhi. Gamma hemolysis was determined in VN5 strain. The finding on Bacillus subtilis strain (VN5) from natto paves the way to a high potential, useful new strain of probiotics.

Structural characterization and physicochemical properties of the exopolysaccharide produced by the moderately halophilic bacterium Chromohalobacter salexigens, strain 3EQS1

A strain, 3EQS1, was isolated from a salt sample taken from Lake Qarun (Fayoum Province, Egypt). On the basis of physiological, biochemical, and phylogenetic analyses, the strain was classified as Chromohalobacter salexigens. By 72 h of growth at 25 °C, strain 3EQS1 produced large amounts (15.1 g L^-1) of exopolysaccharide (EPS) in a liquid mineral medium (initial pH 8.0) containing 10% sucrose and 10% NaCl. The EPS was precipitated from the cell-free culture medium with chilled ethanol and was purified by gel-permeation and anion-exchange chromatography. The molecular mass of the EPS was 0.9 × 10⁶ Da. Chemical analyses, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy showed that the EPS was a linear β-D-(2 → 6)-linked fructan (levan). In aqueous solution, the EPS tended to form supramolecular aggregates with a critical aggregation concentration of 240 µg mL^-1. The EPS had high emulsifying activity (E₂₄, %) against kerosene (31.2 ± 0.4%), sunflower oil (76.9 ± 1.3%), and crude oil (98.9 ± 0.8%), and it also had surfactant properties. A 0.1% (w/v) aqueous EPS solution reduced the surface tension of water by 11.9%. The levan of C. salexigens 3EQS1 may be useful in various biotechnological processes.

Structural and Functional Characterization of Exopolysaccharide Produced by a Novel Isolate Bacillus sp. EPS003

An exopolysaccharide (EPS)-producing soil bacterium was isolated and characterized using 16S rRNA as Bacillus sp. EPS003. EPS was precipitated using ethanol and % composition of total carbohydrate, and protein was determined. Monosaccharide composition was identified using thin layer chromatography (TLC), and it was found to be a levan. Fourier transform infrared (FTIR) spectrum revealed the peaks for carboxyl, hydroxyl, and amide functional groups. ¹H nuclear magnetic resonance (NMR) spectrum further confirmed the presence of fructose monomer. Field emission scanning electron microscopic images (FE-SEM) revealed porous and amorphous characteristics of EPS which was further confirmed with broad peaks in X-ray diffraction (XRD) spectrum. Elemental composition was determined using energy-dispersive X-ray analysis (EDAX). Thermogravimetric analysis (TGA) of EPS resulted in a residual mass of 33.81% at 548 °C indicating high thermal stability. In addition, solubility index and water-holding capacity of EPS were found to be 56% and 264%, respectively, making EPS suitable for various applications. Further, antioxidant potential of EPS was studied using hydroxyl and DPPH radical scavenging assays. In vitro cytotoxicity assessment using L929 cells and SK-MEL-3 cell lines clearly indicated that the EPS produced by the novel isolate Bacillus sp. EPS003 could serve as a potential anticancer agent.

Simulated Digestion and Fecal Fermentation Behaviors of Levan and Its Impacts on the Gut Microbiota

Levan is a microbial fructan widely explored in various fields owing to its excellent physical and biochemical properties. However, little is known about its digestion and fermentation characteristics in vitro. This study evaluated the potential prebiotic properties of levan obtained by enzymatic synthesis. Scanning electron microscopy, Fourier transform infrared spectroscopy, and nuclear magnetic resonance spectroscopy showed that the primary structures of levan remained stable after saliva-gastrointestinal digestion. The microtopography, molecular weight, and functional group of levan were seriously damaged during fecal fermentation. Moreover, the total short-chain fatty acid levels increased significantly, especially for propionic acid, butyric acid, and valeric acid. The 16S rDNA sequencing showed that levan mainly increased the abundance of Firmicutes; in genus levels, certain beneficial bacteria such as Megasphaera and Megamonas genera were remarkably promoted, and the proliferation of harmful genera was inhibited (such as Cedecea and Klebsiella). Overall, this study provided new insights into the potential probiotic mechanism of levan.

A sticky carbohydrate meets a mussel adhesive: Catechol-conjugated levan for hemostatic and wound healing applications

The stickiest natural polysaccharide, levan, plays a role in metalloproteinase activation, which is an important step involved in the healing of injured tissue. However, levan is easily diluted, washed away, and loses adhesion in wet environments, which limits its biomedical applications. Herein, we demonstrate a strategy for fabricating a levan-based adhesive hydrogel for hemostatic and wound healing applications by conjugating catechol to levan. Prepared hydrogels exhibit significantly improved water solubilities, and adhesion strengths to hydrated porcine skin of up to 42.17 ± 0.24 kPa which is more than three-times that of fibrin glue adhesive. The hydrogels also promote rapid blood clotting and significantly faster healing of rat-skin incisions compared to nontreated samples. In addition, levan-catechol exhibited an immune response close to that of the negative control, which is ascribable to its significantly lower endotoxin level compared to native levan. Overall, levan-catechol hydrogels are promising materials for hemostatic and wound healing applications.

Bacterial Exopolysaccharides as Emerging Bioactive Macromolecules: From Fundamentals to Applications

Microbial exopolysaccharides (EPS) are extracellular carbohydrate polymers forming capsules or slimy coating around the cells. EPS can be secreted by various bacterial genera that can help bacterial cells in attachment, environmental adaptation, stress tolerance and are an integral part of microbial biofilms. Several gut commensals (e.g., Lactobacillus, Bifidobacterium) produce EPS that possess diverse bioactivities. Bacterial EPS also has extensive commercial applications in the pharmaceutical and food industries. Owing to the structural and functional diversity, genetic and metabolic engineering strategies are currently employed to increase EPS production. Therefore, the current review provides a comprehensive overview of the fundamentals of bacterial exopolysaccharides, including their classification, source, biosynthetic pathways, and functions in the microbial community. The review also provides an overview of the diverse bioactivities of microbial EPS, including immunomodulatory, anti-diabetic, anti-obesity, and anti-cancer properties. Since several gut microbes are EPS producers and gut microbiota helps maintain a functional gut barrier, emphasis has been given to the intestinal-level bioactivities of the gut microbial EPS. Collectively, the review provides a comprehensive overview of microbial bioactive exopolysaccharides.