Optimization of the expression of levansucrase L17 in recombinant E. coli

Characterization of a novel inulosucrase from Lactiplantibacillus plantarum

Fructansucrases produce fructans by polymerizing the fructose moiety released from sucrose. Here, we describe the recombinant expression and characterization of a unique fructansucrase from Lactiplantibacillus plantarum DKL3 that showed low sequence similarity with previously characterized fructansucrases. The optimum pH and temperature of fructansucrase were found to be 4.0 and 35 °C, respectively. Enzyme activity increased in presence of Ca2+ and distinctly in presence of Mn2+. The enzyme was characterized as an inulosucrase (LpInu), based on the production of an inulin-type fructan as assessed byNMR spectroscopy and methylation analysis. In addition to β-2,1-linkages, the inulin contained a few β-2,1,6-linked branchpoints. High-performance size exclusion chromatography with refractive index detection (HPSEC-RI) revealed the production of inulin with a lower molecular weight compared to other characterized bacterial inulin. LpInu and its inulin product represent novel candidates to be explored for possible food and biomedical applications.

Structure–Function Relationship Studies of Multidomain Levansucrases from Leuconostocaceae Family

Levansucrase LevS from Leuconostoc mesenteroides B-512F is a multidomain fructansucrase (MD-FN) that contains additional domains (ADs) to the catalytic domain. However, the understanding of the effect that these ADs have on enzyme activity remains vague. To this aim, structure-function relationship studies of these LevS ADs were performed by evaluating both biochemical properties and the enzymatic capacity of truncated versions of LevS. Joint participation of the N- and C-terminal domains is essential for stability, activity, specificity, and polymerization processes. Specifically, the N-terminal region is involved in stability, while the transition region plays an essential role in the transfructosylation reaction and polymer elongation. Based on our results, we suggest that ADs interact with each other, adopting a U-shaped topology. The importance of these ADs observed in the MD-FN of the Leuconostocaceae family is not shared by the Lactobacillaceae family. Phylogenetic analysis of LevS AD suggests that MD-FN from Lactobacillaceae and Leuconostocaceae have different evolutionary origins. This is the first study on the structure-function relationship of multidomain levansucrases from the Leuconostocaceae family. Our results point towards the functional role of AD in MD-FN and its involvement in fructan synthesis.

Optimization of Culture Conditions for Secretory Production of 3-Hydroxybutyrate Oligomers Using Recombinant Escherichia coli

Poly(3-hydroxybutyrate) [P(3HB)] is the most representative polyhydroxyalkanoate (PHA), which is a storage polyester for prokaryotic cells. P(3HB)-producing recombinant Escherichia coli secretes diethylene glycol (DEG)-terminated 3HB oligomers (3HBO-DEG) through a PHA synthase-mediated chain transfer and alcoholysis reactions with externally added DEG. The purpose of this study was to optimize the culture conditions for the secretory production of 3HBO-DEG with jar fermenters. First, the effects of culture conditions, such as agitation speed, culture temperature, culture pH, and medium composition on 3HBO-DEG production, were investigated in a batch culture using 250-ml mini jar fermenters. Based on the best culture conditions, a fed-batch culture was conducted by feeding glucose to further increase the 3HBO-DEG titer. Consequently, the optimized culture conditions were reproduced using a 2-L jar fermenter. This study successfully demonstrates a high titer of 3HBO-DEG, up to 34.8 g/L, by optimizing the culture conditions, showing the feasibility of a new synthetic strategy for PHA-based materials by combining secretory oligomer production and subsequent chemical reaction.

A Fructan Sucrase Secreted Extracellular and Purified in One-Step by Gram-Positive Enhancer Matrix Particles

Fructan sucrase is a kind of biological enzyme that catalyzes the synthesis of fructan, and fructan is a polysaccharide product with important industrial application value. In this study, the Fructan sucrase gene of Bacillus subtilis was cloned to plasmid PET-28A-ACMA-Z, and three clones were obtained after the transformation of Escherichia coli BL21, namely BS-FF, BSO, and BS. The clones BS-FF and BSO secreted the recombinant enzymes outside the cells, while the clone BS expressed them inside the cells. The induction experiment results showed that the optimum IPTG concentration in the medium was 0.5 mM and 1.0 mM for clones BS-FF and BSO, respectively, while the incubation conditions were at 28 °C for 8 h. The recombinant fructan sucrase was purified one step using a material called GEM particles. The results indicated that 95.25% of fructan sucrase expressed by the clone BS-FF could be secreted into the extracellular area, and even 98.78% by the clone BSO. With the above purification system, the receiving rate of the recombinant enzyme for clones BS-FF and BSO was 97.70% and 84.99%, respectively. As for the bioactivity of recombinant fructan sucrase, the optimum temperature and pH were 50 °C and 5.6, respectively. The Km and Vmax of it were 33.96 g/L and 0.63 g/(L·min), respectively. The engineered strains with the high extracellular secretion of fructan sucrase were constructed, and a one-step method for the purification of the recombinant enzyme was established. The results might provide a novel selection for the enzymatic production of fructan on a large scale.

A comprehensive study on levan nanoparticles formation: Kinetics and self-assembly modeling

Levan nanoparticles formation is a complicated phenomenon involving simultaneously polymeric reaction kinetics and nanoparticles self-assembly theory. These phenomena are studied in this work with experimental and computational methodologies. Specifically, the effect of different parameters on levan kinetics and nanoparticles production in a cell-free system environment have been studied. Results point out that 37 °C is the best temperature for synthesizing levan as well as the existence of a substrate inhibition effect for polymeric reaction. This work also highlights that raffinose can be used for producing and that an increase on the ratio enzyme-substrate increases the velocity of conversion. However, the previous experimental conditions did not produce an important effect on self-assembly formed levan nanoparticles (always 110 nm) as long as the required levan concentration (CAC) for nanoparticles reorganization is achieved. To have a better understanding of these results, a model was developed to explain numerically levan kinetics and nanoparticle self-assembly. This model was built by taking into account enzyme poisoning effect (also demonstrated experimentally) and a diffusion limited cluster model for the aggregation phenomenon. Simulation results fit properly experimental data and catalytic parameters as well as predicting accurately the value of CAC for producing its reorganization into nanoparticles by self-assembly.

Synthesis of glucooligosaccharides with prebiotic potential by glucansucrase URE 13-300 acceptor reactions with maltose, raffinose and lactose

In the present work, we report an efficient synthesis of glucooligosaccharides (GOSs) with prebiotic potential by novel glucansucrase URE 13-300 from Leuconostoc mesenteroides URE 13 strain. The highest total yield of GOSs with degree of polymerization (DP) from 3 to 6 was obtained with maltose as an acceptor and maltose/sucrose (M/S) ratio 1-136 g/L. An efficient modulation of GOSs composition is achieved by varying the M/S ratio. At M/S = 1, 2, 4 and 7 the content of DP3 products gradually increase from 54.50 to 91.70%. When the M/S ratio was decreased the synthesis of DP>3 GOSs is predominant and reaches 75.60% (M/S = 0.25). In addition, the maltose derived GOSs with DP>3, as well as raffinose and lactose glucosylation products have a branched structure which is prerequisite for increased prebiotic potential. The synthesized GOSs were efficiently metabolized by probiotic strains of Lb. plantarum S26, Lb. brevis S27 and Lb. sakei S16, and the calculated values of specific growth rate (μ) were nearly identical to this on glucose media, when maltose derived GOSs were used as a carbohydrate source. Strain specific features were observed in the utilization of the synthesized GOSs, as well as in the production of lactic acid and acetic acid.