Alginate/PVA Beads for Levan Production by Z ymomonas mobilis

A strategy to reduce the byproduct glucose by simultaneously producing levan and single cell oil using an engineered Yarrowia lipolytica strain displaying levansucrase on the surface

Currently, levan is attracting attention due to its promising applications in the food and biomedical fields. Levansucrase synthesizes levan by polymerizing the fructosyl unit in sucrose. However, a large amount of the byproduct glucose is produced during this process. In this paper, an engineered oleaginous yeast (Yarrowia lipolytica) strain was constructed using a surface display plasmid containing the LevS gene of Gluconobacter sp. MP2116. The levansucrase activity of the engineered yeast strain reached 327.8 U/g of cell dry weight. The maximal levan concentration (58.9 g/l) was achieved within 156 h in the 5-liter fermentation. Over 81.2 % of the sucrose was enzymolyzed by the levansucrase, and the byproduct glucose was converted to 21.8 g/l biomass with an intracellular oil content of 25.5 % (w/w). The obtained oil was comprised of 91.3 % long-chain fatty acids (C16-C18). This study provides new insight for levan production and comprehensive utilization of the byproduct in levan biosynthesis.

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.

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.

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.

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.

The potential use of Zymomonas mobilis for the food industry

Zymomonas mobilis is a gram-negative facultative anaerobic spore, which is generally recognized as a safe. As a promising ethanologenic organism for large-scale bio-ethanol production, Z. mobilis has also shown a good application prospect in food processing and food additive synthesis for its unique physiological characteristics and excellent industrial characteristics. It not only has obvious advantages in food processing and becomes the biorefinery chassis cell for food additives, but also has a certain healthcare effect on human health. Until to now, most of the research is still in theory and laboratory scale, and further research is also needed to achieve industrial production. This review summarized the physiological characteristics and advantages of Z. mobilis in food industry for the first time and further expounds its research status in food industry from three aspects of food additive synthesis, fermentation applications, and prebiotic efficacy, it will provide a theoretical basis for its development and applications in food industry. This review also discussed the shortcomings of its practical applications in the current food industry, and explored other ways to broaden the applications of Z. mobilis in the food industry, to promote its applications in food processing.

Biocatalysts in Synthesis of Microbial Polysaccharides: Properties and Development Trends

Polysaccharides synthesized by microorganisms (bacterial cellulose, dextran, pullulan, xanthan, etc.) have a set of valuable properties, such as being antioxidants, detoxifying, structuring, being biodegradable, etc., which makes them suitable for a variety of applications. Biocatalysts are the key substances used in producing such polysaccharides; therefore, modern research is focused on the composition and properties of biocatalysts. Biocatalysts determine the possible range of renewable raw materials which can be used as substrates for such synthesis, as well as the biochemistry of the process and the rate of molecular transformations. New biocatalysts are being developed for participating in a widening range of stages of raw material processing. The functioning of biocatalysts can be optimized using the following main approaches of synthetic biology: the use of recombinant biocatalysts, the creation of artificial consortia, the combination of nano- and microbiocatalysts, and their immobilization. New biocatalysts can help expand the variety of the polysaccharides’ useful properties. This review presents recent results and achievements in this field of biocatalysis.

Zymomonas mobilis as an emerging biotechnological chassis for the production of industrially relevant compounds

Zymomonas mobilis is a well-recognized ethanologenic bacterium with outstanding characteristics which make it a promising platform for the biotechnological production of relevant building blocks and fine chemicals compounds. In the last years, research has been focused on the physiological, genetic, and metabolic engineering strategies aiming at expanding Z. mobilis ability to metabolize lignocellulosic substrates toward biofuel production. With the expansion of the Z. mobilis molecular and computational modeling toolbox, the potential of this bacterium as a cell factory has been thoroughly explored. The number of genomic, transcriptomic, proteomic, and fluxomic data that is becoming available for this bacterium has increased. For this reason, in the forthcoming years, systems biology is expected to continue driving the improvement of Z. mobilis for current and emergent biotechnological applications. While the existing molecular toolbox allowed the creation of stable Z. mobilis strains with improved traits for pinpointed biotechnological applications, the development of new and more flexible tools is crucial to boost the engineering capabilities of this bacterium. Novel genetic toolkits based on the CRISPR-Cas9 system and recombineering have been recently used for the metabolic engineering of Z. mobilis. However, they are mostly at the proof-of-concept stage and need to be further improved.

Production and сharacterization of the exopolysaccharide from strain Paenibacillus polymyxa 2020

Paenibacillus spp. exopolysaccharides (EPSs) have become a growing interest recently as a source of biomaterials. In this study, we characterized Paenibacillus polymyxa 2020 strain, which produces a large quantity of EPS (up to 68 g/L),and was isolated from wasp honeycombs. Here we report its complete genome sequence and full methylome analysis detected by Pacific Biosciences SMRT sequencing. Moreover, bioinformatic analysis identified a putative levan synthetic operon. SacC and sacB genes have been cloned and their products identified as glycoside hydrolase and levansucrase respectively. The Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectra demonstrated that the EPS is a linear β-(2→6)-linked fructan (levan). The structure and properties of levan polymer produced from sucrose and molasses were analyzed by FT-IR, NMR, scanning electron microscopy (SEM), high performance size exclusion chromatography (HPSEC), thermogravimetric analysis (TGA), cytotoxicity tests and showed low toxicity and high biocompatibility. Thus, P. polymyxa 2020 could be an exceptional cost-effective source for the industrial production of levan-type EPSs and to obtain functional biomaterials based on it for a broad range of applications, including bioengineering.

Preparation of sodium alginate-poly (vinyl alcohol) blend beads for base-triggered release of dinotefuran in Spodoptera litera midgut

This study investigated the ability of dual crosslinked interpenetrating polymer network (IPN) blend beads (DIN:SA/PVA-beads), composed of sodium alginate (SA) and poly (vinyl alcohol) (PVA), as a base-triggered carrier for the controlled release of dinotefuran (DIN) in Spodoptera litera midgut. The blend beads were characterized for morphology, encapsulation efficiency, swelling degree, and in vitro release of the blend beads were characterized. The results revealed that the double-crosslinked gel beads had a tightly interpenetrating network structure and exhibited a satisfactory embedding effect for DIN. The maximum of the DIN loading capacity was approximately 1.01%, with a high encapsulation efficiency of 83.19%. The triggered release of DIN from the blend beads was studied in deionized water (pH 3.0-11.0) via high-performance liquid chromatography (HPLC); it was found that the release rate was higher in alkaline pH conditions than in acidic and neutral conditions. An in vivo dynamics and degradation study also demonstrated that the excellent release characteristics of DIN:SA/PVA-beads in the midgut of S. litera. This study provides a promising controlled-release form of dinotefuran that is more effective and can be used for the targeted control of pests with alkaline midgut.

Assessment of the microbial diversity of Chinese Tianshan tibicos by single molecule, real-time sequencing technology

Chinese Tianshan tibico grains were collected from the rural area of Tianshan in Xinjiang province, China. Typical tibico grains are known to consist of polysaccharide matrix that embeds a variety of bacteria and yeasts. These grains are widely used in some rural regions to produce a beneficial sugary beverage that is slightly acidic and contains low level of alcohol. This work aimed to characterize the microbiota composition of Chinese Tianshan tibicos using the single molecule, real-time sequencing technology, which is advantageous in generating long reads. Our results revealed that the microbiota mainly comprised of the bacterial species of Lactobacillus hilgardii, Lactococcus raffinolactis, Leuconostoc mesenteroides, Zymomonas mobilis, together with a Guehomyces pullulans-dominating fungal community. The data generated in this work helps identify beneficial microbes in Chinese Tianshan tibico grains.