Purification, optimization of assay, and stability studies of dextransucrase isolated from Weissella cibaria JAG8

The Discovery, Molecular Cloning, and Characterization of Dextransucrase LmDexA and Its Active Truncated Mutant from Leuconostoc mesenteroides NN710

Dextransucrases play a crucial role in the production of dextran from economical sucrose; therefore, there is a pressing demand to explore novel dextransucrases with better performance. This study characterized a dextransucrase enzyme, LmDexA, which was identified from the Leuconostoc mesenteroides NN710. This bacterium was isolated from the soil of growing dragon fruit in Guangxi province, China. We successfully constructed six different N-terminal truncated variants through sequential analysis. Additionally, a truncated variant, ΔN190LmDexA, was constructed by removing the 190 amino acids fragment from the N-terminal. This truncated variant was then successfully expressed heterologously in Escherichia coli and purified. The purified ΔN190LmDexA demonstrated optimal hydrolysis activity at a pH of 5.6 and a temperature of 30 °C. Its maximum specific activity was measured to be 126.13 U/mg, with a Km of 13.7 mM. Results demonstrated a significant improvement in the heterologous expression level and total enzyme activity of ΔN190LmDexA. ΔN190LmDexA exhibited both hydrolytic and transsaccharolytic enzymatic activities. When sucrose was used as the substrate, it primarily produced high-molecular-weight dextran (>400 kDa). However, upon the addition of maltose as a receptor, it resulted in the production of a significant amount of oligosaccharides. Our results can provide valuable information for enhancing the characteristics of recombinant dextransucrase and potentially converting sucrose into high-value-added dextran and oligosaccharides.

Dextrans of Weissella cibaria DSM14295: Microbial production, structure and functionality

Lactic acid bacteria of the genus Weissella contribute to spontaneous fermentation in, e.g., sourdough or sauerkraut, but are not registered as starter cultures because of their pending safety assessment. Some strains are able to produce high amounts of exopolysaccharides. This study aims to demonstrate the techno-functionality of five dextrans from W. cibaria DSM14295, produced under varying cultivation conditions, with respect to structural and macromolecular properties. A maximum of 23.1 g/L dextran was achieved by applying the "cold shift" temperature regime. The dextrans differed in molecular mass (9-22∙108 Da, determined by HPSEC-RI/MALLS), intrinsic viscosity (52-73 mL/g), degree of branching (3.8-5.7 % at position O3, determined by methylation analysis) and their side chain length and architecture, determined by HPAEC-PAD after enzymatic hydrolysis. Stiffness of acid gels from milk spiked with these dextrans increased linearly with dextran concentration. Principal component analysis showed that dextrans produced in a semi-defined medium are primarily described by moisture sorption and branching properties, whereas dextrans produced in whey permeate were similar because of their functional and macromolecular properties. Overall, dextrans from W. cibaria DSM14295 have a high potential because of the high production yield and their functionality which can be tailored by the conditions during fermentation.

pH dependent effects of sodium ions on dextransucrase activity in Streptococcus mutans

Dextransuccrase (E.C 2.4.1.5) is a key enzyme in S. mutans for the metabolism of sucrose which helps in the adherence and accumulation of bacteria on tooth surface leading to the formation of dental caries. Dextransuccrase resembles in its catalytic properties with the brush boarder sucrase and exhibits pH dependent inhibitory and stimulatory effects in response to Na⁺. In this communication we studied the effect of monovalent cations on the activity of dextransuccrase from S. mutans. The percentage inhibition of dextransuccrase was 65% at 0.5 mM NaCl which enhanced to 90% at 20 mM sodium concentration. However there was no effect on dextransucrase activity in presence of other monovalent cations (Rb⁺, Cs⁺, and K⁺) tested. Enzyme activity was enhanced 20–24% in acidic pH but was strongly inhibited (59–89%) around neutral and alkaline pH by 0.5–2.0 mM sodium chloride. Upon dialysis, 86% of enzyme activity was restored to control values. There was no effect of 2 mM NaCl on glucosyltransferase activity of the enzyme. Kinetic studies revealed that enzyme showed biphasic effects in response to Na⁺ ions. At acidic pH the enzyme exhibited mixed type of activation affecting both Vmax and Km, while in alkaline pH, the enzyme showed V- type effect reducing Vmax by 74% without affecting Km. The effects of sodium ions on dextransuccrase activity were specific, thus it can be useful to block its catalytic activity, and reducing the cariogenic potential of S. mutans.

•

This is the first report describing the effects of sodium ions on dextransucrase activity in S. mutans, a gram positive bacteria.

•

Dextransucrase activity in S. mutans is essential for metabolism of sucrase a primary substrate for the growth of organism.

•

Data presented herein shows pH dependent biphasic effects of sodium ions on dextransucrase activity similar to that reported in mammalian brush border sucrose.

•

Enzyme activity was stimulated at acidic pH but is strongly inhibited by sodium ions. this may help in reducing the cariogenic potential of S. mutans.

Probiotic potential of Weissella strains isolated from horse feces

In this study, we isolated four Weissella confusa strains from the healthy horse feces to test their potential as equine probiotics. The identification and characteristics of these isolates were determined as per standard methods. Resistance and susceptibility of the isolated strains were tested to low pHs, different heat treatments, commonly used antibiotics and against the pathogenic strains of Salmonella, Pasteurella, Staphylococcus aureus, and Escherichia coli. After 3 h cultural in different pH medium, the 4 strains still had a certain amount of survival above pH 3.0. WH2 and WH4 were still viable at pH2.5. All the isolated strains showed proper growth at 60 °C while no strain survived at 80 °C. The inhibition of α-amylase, the scavenging ability of free radical DPPH· and hydroxyl free radical HO·were also investigated. The results showed that WH4 had highest inhibition rate of α-amylase activity and DPPH· free radical scavenging rate, and the inhibition rate of α-amylase activity was 24.09% and the DPPH· free radical scavenging rate was 35.78%. The inhibition rate ofα-amylase activity and DPPH· scavenging rate of free radicals in the other three strains were about 10%. The clearance rate of hydroxyl radical (HO·) in 4 strains was between 12% and 15%. The antibiotic susceptibilities varied for these four Weisella strains but all of them showed resistance against the frequently used equine antibiotics. All the four strains successfully suppressed the growth of standard strains in in vitro bacteriostasis experiment, which included Salmonella enteritidis (NTNC13349), Escherichia coli (C83902) and Staphylococcus aureus (BNCC186335). they also successfully suppressed the growth of state key laboratory isolating pathogens, which are Pasterurella multocida and Salmonella. Our findings suggest that the isolated strains of Weissella confusa can act as potential equine probiotics and should be explored further.

Purification and characterization of exopolysaccharide produced by Weissella cibaria YB-1 from pickle Chinese cabbage

An exopolysaccharide (EPS) was produced by Weissella cibaria YB-1 isolated from pickle Chinese cabbage. The EPS was purified and characterized. The monosaccharide composition of the EPS was glucose, and its molecular mass was 3.89 × 10⁶ Da, as determined by gas chromatography (GC) and high performance liquid chromatography (HPLC). The structural characterization of purified EPS determined by Fourier transform infrared (FT-IR) spectra and nuclear magnetic resonance (NMR) spectra demonstrated that W. cibaria YB-1 synthesized a linear dextran that predominately had α-(1 → 6) glycosidic linkages with only a few α-(1 → 3) (4.3%) linked branches. The water solubility index (WSI), water holding capacity (WHC) and emulsifying activity (EA) of YB-1 dextran were 95.23 ± 4.45, 287.84 ± 16.23 and 84.43 ± 3.65%, respectively. The in-vitro antioxidant activities of the dextran showed good scavenging effects on superoxide anion radical and hydroxyl radical.

Dextran Utilization During Its Synthesis by Weissella cibaria RBA12 Can Be Overcome by Fed-Batch Fermentation in a Bioreactor

Weissella cibaria RBA12 produced a maximum of 9 mg/ml dextran (with 90% efficiency) using shake flask culture under the optimized concentration of medium components viz. 2% (w/v) of each sucrose, yeast extract, and K₂HPO₄ after incubation at optimized conditions of 20 °C and 180 rpm for 24 h. The optimized medium and conditions were used for scale-up of dextran production from Weissella cibaria RBA12 in 2.5-l working volume under batch fermentation in a bioreactor that yielded a maximum of 9.3 mg/ml dextran (with 93% efficiency) at 14 h. After 14 h, dextran produced was utilized by the bacterium till 18 h in its stationary phase under sucrose depleted conditions. Dextran utilization was further studied by fed-batch fermentation using sucrose feed. Dextran on production under fed-batch fermentation in bioreactor gave 35.8 mg/ml after 32 h. In fed-batch mode, there was no decrease in dextran concentration as observed in the batch mode. This showed that the utilization of dextran by Weissella cibaria RBA12 is initiated when there is sucrose depletion and therefore the presence of sucrose can possibly overcome the dextran hydrolysis. This is the first report of utilization of dextran, post-sucrose depletion by Weissella sp. studied in bioreactor.

The genus Weissella: taxonomy, ecology and biotechnological potential

Bacteria assigned to the genus Weissella are Gram-positive, catalase-negative, non-endospore forming cells with coccoid or rod-shaped morphology (Collins et al., 1993; Björkroth et al., 2009, 2014) and belong to the group of bacteria generally known as lactic acid bacteria. Phylogenetically, the Weissella belong to the Firmicutes, class Bacilli, order Lactobacillales and family Leuconostocaceae (Collins et al., 1993). They are obligately heterofermentative, producing CO2 from carbohydrate metabolism with either d(-)-, or a mixture of d(-)- and l(+)- lactic acid and acetic acid as major end products from sugar metabolism. To date, there are 19 validly described Weissella species known. Weissella spp. have been isolated from and occur in a wide range of habitats, e.g., on the skin and in the milk and feces of animals, from saliva, breast milk, feces and vagina of humans, from plants and vegetables, as well as from a variety of fermented foods such as European sourdoughs and Asian and African traditional fermented foods. Thus, apart from a perceived technical role of certain Weissella species involved in such traditional fermentations, specific Weissella strains are also receiving attention as potential probiotics, and strain development of particularly W. cibaria strains is receiving attention because of their high probiotic potential for controlling periodontal disease. Moreover, W. confusa and W. cibaria strains are known to produce copius amounts of novel, non-digestible oligosaccharides and extracellular polysaccharides, mainly dextran. These polymers are receiving increased attention for their potential application as prebiotics and for a wide range of industrial applications, predominantly for bakeries and for the production of cereal-based fermented functional beverages. On the detrimental side, strains of certain Weissella species, e.g., of W. viridescens, W. cibaria and W. confusa, are known as opportunistic pathogens involved in human infections while strains of W. ceti have been recently recongnized as etiological agent of "weissellosis," which is a disease affecting farmed rainbow trouts. Bacteria belonging to this species thus are important both from a technological, as well as from a medical point of view, and both aspects should be taken into account in any envisaged biotechnological applications.

Cloning and characterization of a Weissella confusa dextransucrase and its application in high fibre baking

Wheat bran offers health benefits as a baking ingredient, but is detrimental to bread textural quality. Dextran production by microbial fermentation improves sourdough bread volume and freshness, but extensive acid production during fermentation may negate this effect. Enzymatic production of dextran in wheat bran was tested to determine if dextran-containing bran could be used in baking without disrupting bread texture. The Weissella confusa VTT E-90392 dextransucrase gene was sequenced and His-tagged dextransucrase Wc392-rDSR was produced in Lactococcus lactis. Purified enzyme was characterized using ¹⁴C-sucrose radioisotope and reducing value-based assays, the former yielding K_m and V_max values of 14.7 mM and 8.2 μmol/(mg∙min), respectively, at the pH optimum of 5.4. The structure and size of in vitro dextran product was similar to dextran produced in vivo. Dextran (8.1% dry weight) was produced in wheat bran in 6 h using Wc392-rDSR. Bran with and without dextran was used in wheat baking at 20% supplementation level. Dextran presence improved bread softness and neutralized bran-induced volume loss, clearly demonstrating the potential of using dextransucrases in bran bioprocessing for use in baking.

The influence of pH, polyethylene glycol and polyacrylic acid on the stability of stem bromelain

Enzyme stability is critical in biotechnology, pharmaceutical and cosmetic industries. Investigations on this subject have drawn attention because of its practical application. Bromelain is a thiol-endopeptidase, obtained from pineapple (Ananas comosus), known for its clinical and therapeutic applications, particularly to selective burn debridement and improvement of antibiotic action and anti-inflammatory activities. To date, the use of bromelain in pharmacological or industrial applications is limited, due to commercial availability, costs, and sensitivity to pH and temperature. Therefore, a better understanding of enzyme stability would be of great interest. The aim of this study was to evaluate bromelain activity and stability in several pH (2.0 to 8.0) and in polyethylene glycol and polyacrylic acid solutions. We observed that bromelain was able to maintain its stability at pH 5.0 for the temperatures studied. PEG solutions increased bromelain stability, but PAA solutions had the opposite effect.

Weissella confusa Cab3 dextransucrase: properties and in vitro synthesis of dextran and glucooligosaccharides

Food-derived Weissella spp. have gained attention during recent years as efficient dextran producers. Weissella confusa Cab3 dextransucrase (WcCab3-DSR) was isolated applying PEG fractionation and used for in vitro synthesis of dextran and glucooligosaccharides. WcCab3-DSR had a molar mass of 178 kDa and was activated by Co(2+) and Ca(2+) ions. Glycerol and Tween 80 enhanced enzyme stability, and its half-life at 30°C increased from 10h to 74 h and 59 h, respectively. The (1)H and (13)C NMR spectral analysis of the produced dextran confirmed the presence of main chain α-(1→6) linkages with only 3.0% of α-(1→3) branching, of which some were elongated. An HPSEC analysis in DMSO revealed a high molecular weight of 1.8 × 10(7)g/mol. Glucooligosaccarides produced through the acceptor reaction with maltose, were analyzed with HPAEC-PAD and ESI-MS/MS. They were a homologous series of isomaltooligosaccharides with reducing end maltose units. To the best of our knowledge, this is a first report on native W. confusa dextransucrase.