Biosynthesis of inulin from sucrose using inulosucrase from Lactobacillus gasseri DSM 20604

A review of fructosyl-transferases from catalytic characteristics and structural features to reaction mechanisms and product specificity

Carbohydrate-active enzymes are accountable for the synthesis and degradation of glycosidic bonds among diverse carbohydrates. Fructosyl-transferases represent a subclass of these enzymes, employing sucrose as a substrate to generate fructooligosaccharides (FOS) and fructan polymers. This category primarily includes levansucrase (LS, EC 2.4.1.10), inulosucrase (IS, EC 2.4.1.9), and β-fructofuranosidase (Ffase, EC 3.2.1.26). These three enzymes possess a similar five-bladed β-propeller fold and employ an anomer-retaining reaction mechanism mediated by nucleophiles, transition state stabilizers, and general acids/bases. However, they exhibit distinct product profiles, characterized by variations in linkage specificity and molecular mass distribution. Consequently, this article comprehensively explores recent advancements in the catalytic characteristics, structural features, reaction mechanisms, and product specificity of levansucrase, inulosucrase, and β-fructofuranosidase (abbreviated as LS, IS, and Ffase, respectively). Furthermore, it discusses the potential for modifying catalytic properties and product specificity through structure-based design, which enables the rational production of custom fructan and FOS.

Inulin from halophilic archaeon Haloarcula: Production, chemical characterization, biological, and technological properties

Halophilic archaea are capable of producing fructans, which are fructose-based polysaccharides. However, their biochemical characterization and biological and technological properties have been scarcely studied. The aim of this study was to evaluate the production, chemical characterization, biological and technological properties of a fructan inulin-type biosynthesized by a halophilic archaeon. Fructan extraction was performed through ethanol precipitation and purification by diafiltration. The chemical structure was elucidated using Fourier Transform-Infrared Spectroscopy and Nuclear Magnetic Resonance (NMR). Haloarcula sp. M1 biosynthesizes inulin with an average molecular weight of 8.37 × 106 Da. The maximal production reached 3.9 g of inulin per liter of culture within seven days. The glass transition temperature of inulin was measured at 138.85 °C, and it exhibited an emulsifying index of 36.47 %, which is higher than that of inulin derived from chicory. Inulin from Haloarcula sp. M1 (InuH) demonstrates prebiotic capacity. This study represents the first report on the biological and technological properties of inulin derived from halophilic archaea.

Physicochemical Characterization of Dextran HE29 Produced by the Leuconostoc citreum HE29 Isolated from Traditional Fermented Pickle

In this study, lactic acid bacteria (LAB) strains were isolated from traditional fermented pickles, and among the identified strains, Leuconostoc citreum HE29 with a strong slimy colony profile was further selected to determine the physicochemical and techno-functional properties of its exopolysaccharide (EPS). Glucose was the only sugar monomer in the core unit of EPS HE29 detected by HPLC analysis, and glucan HE29 revealed 7.3 kDa of molecular weight. Structural characterization of glucan HE29 by 1H and 13C NMR spectroscopy analysis demonstrated that EPS HE29 was a dextran-type EPS containing 5.3% levels of (1 → 3)-linked α-D-glucose units. This structural configuration was also supported by FT-IR analysis, which also demonstrated the functional groups within the dextran HE29 structure. In terms of thermal properties detected by TGA and DSC analysis, dextran HE29 demonstrated a degradation temperature of around 280 °C, showing its strong thermal features. A semi-crystalline nature was observed for dextran HE29 detected by XRD analysis. Finally, AFM and SEM analysis revealed tangled network-like properties and web-like branched structures for dextran HE29, respectively. These findings suggest the importance of plant-based fermented products as LAB sources in obtaining novel EPS structures with potential techno-functional roles.

New progress in the identifying regulatory factors of exopolysaccharide synthesis in lactic acid bacteria

The exopolysaccharides (EPSs) of lactic acid bacteria (LAB) have presented various bioactivities and beneficial characteristics, rendering their vast commercial value and attracting a broad interest of researchers. The diversity of EPS structures contributes to the changes of EPS functions. However, the low yield of EPS of LAB has severely limited these biopolymers' comprehensive studies and applications in different areas, such as functional food, health and medicine fields. The clarification of biosynthesis mechanism of EPS will accelerate the synthesis and reconstruction of EPS. In recent years, with the development of new genetic manipulation techniques, there has been significant progress in the EPS biosynthesis mechanisms in LAB. In this review, the structure of LAB-derived EPSs, the EPS biosynthesis basic pathways in LAB, the EPS biosynthetic gene cluster, and the regulation mechanism of EPS biosynthesis will be summarized. It will focus on the latest progress in EPS biosynthesis regulation of LAB and provide prospects for future related developments.

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.

High-yield production and purification of prebiotic inulin-type fructooligosaccharides

Due to the health-promoting effects and functional properties of inulin-type fructooligosaccharides (I-FOS), the global market for I-FOS is constantly growing. Hence, there is a continuing demand for new, efficient biotechnological approaches for I-FOS production. In this work, crude inulosucrase InuGB-V3 from Lactobacillus gasseri DSM 20604 was used to synthesize I-FOS from sucrose. Supplementation with 1 mM CaCl2, a pH of 3.5–5.5, and an incubation temperature of 40 °C were found to be optimal production parameters at which crude inulosucrase showed high conversion rates, low sucrose hydrolysis, and excellent stability over 4 days. The optimal process conditions were employed in cell-free bioconversion reactions. By elevating the substrate concentration from 570 to 800 g L−1, the I-FOS concentration and the synthesis of products with a low degree of polymerization (DP) could be increased, while sucrose hydrolysis was decreased. Bioconversion of 800 g L−1 sucrose for 20 h resulted in an I-FOS-rich syrup with an I-FOS concentration of 401 ± 7 g L−1 and an I-FOS purity of 53 ± 1% [w/w]. I-FOS with a DP of 3–11 were synthesized, with 1,1-kestotetraose (DP4) being the predominant transfructosylation product. The high-calorie sugars glucose, sucrose, and fructose were removed from the generated I-FOS-rich syrup using activated charcoal. Thus, 81 ± 5% of the initially applied I-FOS were recovered with a purity of 89 ± 1%.

Variability of Bacterial Homopolysaccharide Production and Properties during Food Processing

Various homopolysaccharides (HoPSs) can be produced by bacteria: α- and β-glucans, β-fructans and α-galactans, which are polymers of glucose, fructose and galactose, respectively. The synthesis of these compounds is catalyzed by glycosyltransferases (glycansucrases), which are able to transfer the monosaccharides in a specific substrate to the medium, which results in the growth of polysaccharide chains. The range of HoPS sizes is very large, from 104 to 109 Da, and mostly depends on the carbon source in the medium and the catalyzing enzyme. However, factors such as nitrogen nutrients, pH, water activity, temperature and duration of bacterial culture also impact the size and yield of production. The sequence of the enzyme influences the structure of the HoPS, by modulating the type of linkage between monomers, both for the linear chain and for the ramifications. HoPSs' size and structure have an effect on rheological properties of some foods by their influence on viscosity index. As a consequence, the control of structural and environmental factors opens ways to guide the production of specific HoPS in foods by bacteria, either by in situ or ex situ production, but requires a better knowledge of HoPS production conditions.

Characterization of a novel fructosyltransferase InuCA from Lactobacillus crispatus that attaches to the cell surface by electrostatic interaction

Fructosyltransferases (FTases), a group of carbohydrate-active enzymes, synthesize fructooligosaccharides (FOS) and fructans, which are promising prebiotics for human health. Here we originally identified a novel FTase InuCA from L. crispatus, a dominant species in the vaginal microbiotas of human. InuCA was characterized by a shortest C-terminus and the highest isoelectric point among the reported Lactobacillus FTases. InuCA was an inulosucrase and produced a serial of FOS using sucrose as substrate at a moderate temperature. Surprisingly, the C-terminal deletion mutant synthesized oligosaccharides with fructosyl chain longer than that of the wild type, suggesting that the C-terminal part blocked the binding of long-chain receptor. Moreover, InuCA bound to the cell surface by electrostatic interaction, which was dependent on the environmental pH and represented a distinctive binding mode in FTases. The catalytic and structural properties of InuCA will be contributed to the FTases engineering and the knowledge of the adaptation of L. crispatus in the vaginal environment. Importance L. crispatus is one of the most important species in human vaginal microbiotas and its persistence is strongly negatively correlated with the vaginal diseases. Our research reveals that a novel inulosucrase InuCA is present in L. cirspatus. InuCA keeps the ability to synthesize prebiotic fructo-oligosaccharides, although it lacks a large part of the C-terminal region compared to other FTases. Remarkably, the short C-terminus of InuCA blocks the transfructosylation activity for producing oligosaccharides with longer chain, which is meaningful to the directional modification of FTases and the oligosaccharide products. Besides the catalytic activity, InuCA is anchored on the cell surface dependent on the environmental pH and may be also involved in the adhesion of L. crispatus to the vaginal epithelial cells. Since L. crispatus plays an essential role in the normal vaginal micro-ecosystem, the described work will be helpful to elucidate the functional genes and colonization mechanism of the dominant species.

Improving the Thermostability and Catalytic Activity of an Inulosucrase by Rational Engineering for the Biosynthesis of Microbial Inulin

Thermostability and enzymatic activity are two vital indexes determining the application of an enzyme on an industrial scale. A truncated inulosucrase, Laga-ISΔ138-702, from Lactobacillus gasseri showed high catalysis activity. To further enhance its thermostability and activity, multiple sequence alignment (MSA) and rational design based on the modeled structure were performed. Variants A446E, S482A, I614M, and A627S were identified with an improved denaturation temperature (T_m) of more than 1 °C. A combinational mutation method was further carried out to explore the synergistic promotion effects of single-point mutants. Additionally, 33 residues at the N-terminus were truncated to construct mutant M4^N-33. The half-life of M4^N-33 at 55 °C increased by 120 times compared to that of Laga-ISΔ138-702, and the relative activity of M4^N-33 increased up to 152% at the optimal pH and temperature (pH 5.5 and 60 °C). Molecular dynamics (MD) simulations illustrated the decreased b-factor of the surface loop of M4^N-33.

Characterization of a nanoparticulate exopolysaccharide from Leuconostoc holzapfelii KM01 and its potential application in drug encapsulation

Fermentation of Lactic Acid Bacteria (LAB) is considered to be a sustainable approach for polysaccharide production. Herein, exopolysaccharide (EPS)-producing LAB strain KM01 was isolated from Thai fermented dessert, Khao Mak, which was then identified as Leuconostoc holzapfelii. High-performance anion-exchange chromatography, nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy suggested that the KM01 EPS comprises α-1,6-linked glucosides. The molecular weight of KM01 EPS was around 500 kDa, but it can form large aggregates formation (MW > 2000 kDa) in an aqueous solution, judged by transmission electron microscopy and dynamic light scattering to be around 150 nm in size. Furthermore, this KM01 EPS form highly viscous hydrogels at concentrations above 5% (w/v). The formation of hydrogels and nanoparticle of KM01 EPS was found to be reversible. Finally, the suitability of KM01 EPS for biomedical applications was demonstrated by its lack of cytotoxicity and its ability to form complexes with quercetin. Unlike the common α-1,6-linked dextran, KM01 EPS can enhance the solubility of quercetin significantly.

Efficient biosynthesis of lacto-N-neotetraose by a novel β-1,4-galactosyltransferase from Aggregatibacter actinomycetemcomitans NUM4039

Lacto-N-neotetraose (LNnT) is a unique tetrasaccharide naturally occurring in human milk, as an important member of human milk oligosaccharides. Because of promising beneficial effects, it has been commercially added as a functional fortifier in infant formula. β-1,4-Galactosyltransferase (β-1,4-GalT) catalyzes LNnT biosynthesis from uridine 5'-diphospho-galactose (UDP-Gal) to lacto-N-triose II (LNT II). There have been only two LNnT-producing bacterial β-1,4-GalTs, including the ones from Neisseria meningitidis and Histophilus somni. In this study, a novel LNnT-producing β-1,4-GalT was identified from Aggregatibacter actinomycetemcomitans. The enzyme was easily overexpressed in E. coli in soluble form. It displayed much higher transglycosylation versus hydrolysis activity, indicating its great potential in LNnT biosynthesis. The enzyme produced 13 mM LNnT from 20 mM LNT II and 60 mM UDP-Gal, with the yield of 65 % on LNT II and very low level of UDP-Gal hydrolysis. Therefore, it could be considered as a good candidate for the practical LNnT production.

Improving the catalytic behaviors of Lactobacillus-derived fructansucrases by truncation strategies

Fructansucrases (FSs), including inulosucrase (IS) and levansucrase (LS), are the members of the Glycoside Hydrolase family 68 (GH68) enzymes. IS and LS catalyze the polymerization of the fructosyl moiety from sucrose to inulin- and levan-type fructans, respectively. Lactobacillus-derived FSs have relatively extended N- and C-terminal sequences. However, the functional roles of these sequences in their enzymatic properties and fructan biosynthesis remain largely unknown. Limosilactobacillus reuteri (basionym: Lactobacillus reuteri) 121 could produce both IS and LS, abbreviated as Lare121-IS and Lare121-LS, respectively. In this study, it was found that the terminal truncation displayed an obvious effect on their activities and the N-terminal truncated variants, Lare121-ISΔ177-701 and Lare121-LSΔ154-686, displayed the highest activities. Melting temperature (T_m) and the thermostability at 50 °C were measured to evaluate the stability of various truncated versions, revealing the different effects of N-terminal on the stability. The average molecular weight and polymerization degree of the fructans produced by different truncated variants did not change considerably, indicating that N-terminal truncation had low influence on fructan biosynthesis. In addition, it was found that N-terminal truncation could also improve the activity of other reported FSs from Lactobacillus species.

Difructose anhydride III: a 50-year perspective on its production and physiological functions

Production and applications of difructose anhydride III (DFA-III) have attracted considerable attention because of its versatile physiological functions. Recently, large-scale production of DFA-III has been continuously explored, which opens a horizon for applications in the food and pharmaceutical industries. This review updates recent advances involving DFA-III, including: biosynthetic strategies, purification, and large-scale production of DFA-III; physiological functions of DFA-III and related mechanisms; DFA-III safety evaluations; present applications in food systems, existing problems, and further research prospects. Currently, enzymatic synthesis of DFA-III has been conducted both industrially and in academic research. Two biosynthetic strategies for DFA-III production are summarized: single- and double enzyme-mediated. DFA-III purification is achieved via yeast fermentation. Enzyme membrane bioreactors have been applied to meet the large-scale production demands for DFA-III. In addition, the primary physiological functions of DFA-III and their underlying mechanisms have been proposed. However, current applications of DFA-III are limited. Further research regarding DFA-III should focus on commercial production and purification, comprehensive study of physiological properties, extensive investigation of large-scale human experiments, and expansion of industrial applications. It is worthy to dig deep into potential application and commercial value of DFA-III.

High-resolution method for isocratic HPLC analysis of inulin-type fructooligosaccharides

In recent decades, strategies to improve human health by modulating the gut microbiota have developed rapidly. One of the most prominent is the use of prebiotics, which can lead to a higher abundance of health-promoting microorganisms in the gut. Currently, oligosaccharides dominate the prebiotic sector due to their ability to promote the growth and activity of probiotic bacteria selectively. Extensive efforts are made to develop effective production strategies for the synthesis of prebiotic oligosaccharides, including the use of microbial enzymes. Within the genus Lactobacillus, several inulosucrases have been identified, which are suitable for the synthesis of prebiotic inulin-type fructooligosaccharides (inulin-FOS). In this study, a truncated version of the inulosucrase from Lactobacillus gasseri DSM 20604 was used for the efficient synthesis of inulin-FOS. Product titers of 146.2 ± 7.4 g inulin-FOSL^-1 were achieved by the catalytic activity of the purified recombinant protein InuGB-V3. A time and resource-saving HPLC method for rapid analysis of inulin-FOS in isocratic mode was developed and optimized, allowing baseline separated analysis of inulin-FOS up to a degree of polymerization (DP) of five in less than six minutes. Long-chain inulin-FOS with a DP of 17 can be analyzed in under 45 min. The developed method offers the advantages of isocratic HPLC analysis, such as low flow rates, high sensitivity, and the use of a simple, inexpensive chromatographic setup. Furthermore, it provides high-resolution separation of long-chain inulin-FOS, which can usually only be achieved with gradient systems.

Fermentation by Probiotic Lactobacillus gasseri Strains Enhances the Carotenoid and Fibre Contents of Carrot Juice

Carrot juice (straight, 8.5 Brix and concentrated, 15.2 Brix) was fermented by lactic acid bacteria (Lactobacillus gasseri strain DSM 20604 or DSM 20077). Fermentation enhanced the nutritional profile of carrot juice. There was a greater sugar reduction (27%) in fermented straight carrot juices than in the fermented concentrated juices (15%). The sugar reduction was independent of the strain used for fermentation. The two L. gasseri strains synthesised fructosyltransferase enzymes during fermentation of carrot juice samples that enabled conversion of simple sugars primarily into polysaccharides. The level of conversion to polysaccharides was dependent on the L. gasseri strain and juice concentration. Fermentation of carrot juice by L. gasseri enables the production of a nutritionally-enhanced beverage with reduced calorie and prebiotic potential. An additional benefit is the increased carotenoid content observed in straight and concentrated juices fermented by Lactobacillus gasseri DSM 20077 and the concentrated juice fermented by Lactobacillus gasseri DSM 20604.

Conserved Calcium-Binding Residues at the Ca-I Site Involved in Fructooligosaccharide Synthesis by Lactobacillus reuteri 121 Inulosucrase

Inulosucrase is an enzyme that synthesizes inulin-type β-2,1-linked fructooligosaccharides (IFOS) from sucrose. Previous studies have shown that calcium is important for the activity and stability of Lactobacillus reuteri 121 inulosucrase (LrInu). Here, mutational analyses of four conserved calcium-binding site I (Ca-I) residues of LrInu, Asp418, Gln449, Asn488, and Asp520 were performed. Alanine substitution for these residues not only reduced the stability and activity of LrInu, but also modulated the pattern of the IFOS produced. Circular dichroism spectroscopy and molecular dynamics simulation indicated that these mutations had limited impact on the overall conformation of the enzyme. One of Ca-I residues most critical for controlling LrInu-mediated polymerization of IFOS, Asp418, was also subjected to mutagenesis, generating D418E, D418H, D418L, D418N, D418S, and D418W. The activity of these mutants demonstrated that the IFOS chain length could be controlled by a single mutation at the Ca-I site.

Production and Physicochemical Properties of Food-Grade High-Molecular-Weight Lactobacillus Inulin

Inulin has been widely applied in food, pharmaceuticals, and many other fields because of its versatile physicochemical properties and physiological functions. Previous research showed that inulosucrase from microorganisms could produce higher-molecular-weight inulin than vegetal inulin. Herein, a food-grade recombinant Bacillus subtilis expression system was constructed to produce inulosucrase from Lactobacillus gasseri DSM 20604 without antibiotic resistance genes. The produced inulosucrase was used to biosynthesize inulin with an average molecular weight of 5.8 × 10⁶ Da. The physicochemical properties of the produced Lactobacillus inulin were evaluated including microstructure, thermal characteristics, crystallinity, rheological behaviors, and storage stability. By comparing with vegetal inulin and other polymers, the biosynthesized microbial inulin showed some superior properties, such as better gel-forming capability and storage stability in aqueous solution than vegetal inulin. These results opened up possibilities for further investigations aimed at developing microbial inulin in the food industry.

Inulin as a multifaceted (active) substance and its chemical functionalization: From plant extraction to applications in pharmacy, cosmetics and food

This review is aimed at critically discussing a collection of research papers on Inulin (INU) in different scientific fields. The first part of this work gives an overview on the main characteristics of native INU, including production, applications in food or cosmetics industries, its benefits on human health as well as its main nutraceutical properties. A particular focus is dedicated to the extraction techniques and to the specific effects of INU on intestinal microbiota. Other than in food industry, the number of INU applications increases dramatically in the pharmaceutical field especially due to its simple chemical functionalization. Thus, aim of this review is also to give practical examples of chemical functionalization performed on INU also by including critical comments based on the direct experience of the Authors. With this aim, a full paragraph is dedicated to practical chemical experiences useful to reduce the efforts when establishing new experimental conditions. Moreover, the pharmaceutical technology is also taken in special consideration by underlining the aspects leading at the preparation of formulations based on INU. At the end of the review, a critical paragraph is intended to feed the scientists' curiosity on this versatile polysaccharide.

Highly porous core-shell chitosan beads with superb immobilization efficiency for Lactobacillus reuteri 121 inulosucrase and production of inulin-type fructooligosaccharides

With the aim to overcome the limitations of hydrogel chitosan beads (HGBs), various types of chitosan, core-shell chitosan beads (CSBs), and dried chitosan beads (DBs) were synthesized. Physical and chemical properties were compared with those of HGBs. CSBs were proved to be an effective support because they displayed higher stability and capacity over the HGBs, and thus, were selected for enzyme immobilization. Recombinant inulosucrase (INU) from Lactobacillus reuteri 121 was immobilized on CSBs using glutaraldehyde as a cross-linker. Immobilized biocatalysts (INU-CSBs) were then used for the synthesis of inulin-type fructooligosaccharide (IFOS). Biochemical characterization revealed that the optimum pH of both INU-CSBs and free enzyme was unaltered at 5.5 whereas the optimum temperature of INU-CSBs shifted from 50 °C to 60 °C. Moreover, pH stability and thermostability of INU-CSBs significantly improved. For batch synthesis of IFOS, INU-CSBs retained approximately 45% of their initial catalytic activity after being reused for 12 cycles. IFOS was also continuously synthesized in a fixed-bed bioreactor for a reaction duration of at least 30 h. The high efficiency of INU-CSBs makes them very attractive for industrial applications.