Welan gum: Microbial production, characterization, and applications

Optimization of welan gum extraction and purification using lysozyme and alkaline protease

Welan gum, a natural polysaccharide produced by Sphingomonas sp. ATCC 31555, has attracted considerable attention in the scientific community due to its desirable properties. However, challenges, such as high viscosity, residual bacterial cells, carotenoids, and protein complexation, hinder the widespread application of welan gum. In this study, we established a method for the extraction and purification of welan gum using a synergistic approach with lysozyme and alkaline protease. Lysozyme hydrolysis conditions were optimized by applying response surface methodology, and the best results for bacterial cell removal were achieved at 11 000 U/g, 44 °C, and pH 9 after 3 h of treatment. Subsequently, we evaluated protein hydrolysis through computer simulation and identified alkaline protease as the most suitable enzyme. Through experimental investigations, we found that the optimal conditions for alkaline protease hydrolysis were 7500 U/g, 50 °C, pH 10, and 600 rpm. These conditions resulted in a sugar recovery rate of 76.1%, carotenoid removal rate of 89.5%, bacterial removal rate of 95.2%, and protein removal rate of 87.3% after 3 h of hydrolysis. The purified welan gum exhibited high transparency and purity. Structural characterization and antioxidant activity evaluation revealed that enzymatically purified welan gum has potential application prospects. Our study provides valuable insights into the optimal method for the enzymatic extraction and purification of welan gum. Such a method is conducive to the development of the multiple potential applications of welan gum. KEY POINTS: • A novel process for the synergistic purification of welan gum using lysozyme and alkaline protease was established. • In silico virtual digestion was employed to select the purification enzyme. • Welan gum with high transparency and purity was obtained.

Glycerol-driven adaptive evolution for the production of low-molecular-weight Welan gum: Characterization and activity evaluation

Through adaptive laboratory evolution (ALE) of Sphingomonas sp. ATCC 31555, fermentation for production of low-molecular-weight welan gum (LMW-WG) was performed using glycerol as sole carbon source. During ALE, GPC-MALS analysis revealed a gradual decrease in WG molecular weight with the increase of adaptation cycles, accompanied by changes in solution conformation. LMW-WG was purified and structurally analyzed using GPC-MALS, monosaccharide composition analysis, infrared spectroscopy, NMR analysis, atomic force microscopy, and scanning electron microscopy. Subsequently, LMW-WG obtains hydration, transparency, antioxidant activity, and rheological properties. Finally, an in vitro simulation colon reactor was used to evaluate potential prebiotic properties of LMW-WG as dietary fiber. Compared with WG produced using sucrose as substrate, LMW-WG exhibited a fourfold reduction in molecular weight while maintaining moderate viscosity. Structurally, L-Rha nearly completely replaced L-Man. Furthermore, LMW-WG demonstrated excellent hydration, antioxidant activity, and high transparency. It also exhibited resistance to saliva and gastrointestinal digestion, showcasing a favorable colonization effect on Bifidobacterium, making it a promising symbiotic agent.

Engineering Bacterial Biomanufacturing: Characterization and Manipulation of Sphingomonas sp. LM7 Extracellular Polymers

Biologically produced materials are an attractive alternative to traditional materials such as metals and plastics and offer improved functionalities such as better biodegradability and biocompatibility. Polysaccharides are an example of a biologically produced materials that can have a range of chemical and physical properties including high stiffness to weight ratios and thermal stability. Biomanufactured bacterial polysaccharides can come with many advantages such as being non-toxic and are mechanically robust relative to proteins and lipids, which are also secreted by bacteria to generate a biofilm. One major goal in biomanufacturing is to produce quality material quickly and cost-effectively. Biomanufacturing offers additional benefits compared to traditional manufacturing including low resource investment and equipment requirements, providing an alternative to sourcing fossil fuel byproducts, and relatively low temperatures needed for production. However, many biologically produced materials require complex and lengthy purification processes before use. This paper 1) identifies the material properties of a novel polysaccharide, dubbed promonan, isolated from the extracellular polymeric substances of Sphingomonas sp. LM7; 2) demonstrates that these properties can be manipulated to suit specific applications; and 3) presents two alternative methods of processing to shorten purification time by more than 50% while maintaining comparable material.

Modification of Welan gum with poly(2-oxazoline) to obtain thermoviscosifying polymer for enhanced oil recovery

Thermoviscosifying polymers refer to a category of smart materials that exhibit a responsive behavior to environmental stimuli, specifically demonstrating a natural rise in viscosity of solutions as the temperature increases. The temperature-dependent behavior exhibited by thermally viscous polymers renders them potentially advantageous in the context of Enhanced Oil Recovery (EOR). There exists a dearth of research pertaining to the application of thermoviscosifying polymer for better recovery in reservoirs characterized by high temperatures and high salt content. In order to tackle the mentioned concerns, this study examined the utilization of welan gum modified with poly(2-oxazoline) as thermally responsive chain segments to enhance viscosity. The objective was to evaluate the ability to enhance viscosity under thermal conditions and to assess their effectiveness in displacement of reservoir oil in high temperature and high salt environments. This study aimed to establish a theoretical framework for understanding the correlation between the molecular structure and performance of novel thermally viscous polymers. Additionally, it sought to offer practical insights into designing the molecular structure of thermally viscous polymers suitable for polymer flooding in high temperature and high salt environments. Furthermore, the study proposed the application of these new thermoviscosifying polymers for EOR.

NMR analysis of the side-group substituents in welan gum in comparison to gellan gum

The physicochemical properties and applications of polysaccharides are highly dependent on their chemical structures, including the monosaccharide composition, degree of substitution, and position of substituent groups in the backbone. The occurrence of side groups or side chains in the chain backbone of polysaccharides is often an essential factor influencing their conformational and physicochemical properties. Welan gum produced by the fermentation of Sphingomonas sp. ATCC 31555 microorganisms has been widely used in food, construction, and oil drilling fields. While understanding the physicochemical properties of welan gum solution has been highly developed, there is still little information about the determination strategy of the glycosyl side groups in welan gum. In this study, the NMR method was established to quantitatively determine the substituent groups in the chain backbone of welan gum. The delicate chemical structures of welan gum obtained at different fermentation conditions were clarified. The composition and content of side substituents were also identified by high-performance liquid chromatography to confirm the accuracy of NMR analysis. The quantitative determination of substituent groups in gellan gum based on NMR analysis was also elaborated for comparison. This work provides insights for profoundly understanding the structure-function relationship of welan gum.

Rheological characterization of artificial paenan compositions produced by Paenibacillus polymyxa DSM 365

Microbial exopolysaccharides offer a sustainable alternative to petroleum-based rheological modifiers. Recent studies revealed that the heteroexopolysaccharide produced by Paenibacillus polymyxa is composed of three distinct biopolymers, referred to as paenan I, II and III. Using CRISPR-Cas9 mediated knock-out variants of glycosyltransferases, defined polysaccharide compositions were produced and rheologically characterized in detail. The high viscosity and gel-like character of the wildtype polymer is proposed to originate from the non-covalent interaction between a pyruvate residue of paenan I and the glucuronic acid found in the backbone of paenan III. Paenan II conveys thermostable properties to the exopolysaccharide mixture. In contrast to the wildtype polymer mixture, knock-out variants demonstrated significantly altered rheological behavior. Using the rheological characterization performed in this study, tailor-made paenan variants and mixtures can be generated to be utilized in a wide range of applications including thickening agents, coatings, or high-value biomedical materials.

Microbial exopolysaccharide: Sources, stress conditions, properties and application in food and environment: A comprehensive review

Microbial glucan or exopolysaccharides (EPS) have caught an eye of researchers from decades. The unique characteristics of EPS make it suitable for various food and environmental applications. This review overviews the different types of exopolysaccharides, sources, stress conditions, properties, characterization techniques and applications in food and environment. The yield and production condition of EPS is a major factor affecting the cost and its applications. Stress conditions are very important as it stimulates the microorganism for enhanced EPS production and affects its properties. As far as application is concerned specific properties of EPS such as, hydrophilicity, less oil uptake behavior, film forming ability, adsorption potential have applications in both food and environment sector. Novel and improved method of production, feed stock and right choice of microorganisms with stress conditions are critical for desired functionality and yield of the EPS.

Physicochemical and Structural Characterization of Alkali-Treated Biopolymer Sphingan WL Gum from Marine Sphingomonas sp. WG

Sphingan WL gum (WL), a kind of exopolysaccharide, is produced by Sphingomonas sp. WG, which was screened from sea mud samples of Jiaozhou Bay by our group. The solubility of WL was investigated in this work. First, 1 mg/mL of WL solution was stirred at room temperature for at least 2 h to obtain a uniform opaque liquid, and further the solution became clear with the increased NaOH and stirring time. Subsequently, the structural features, solubility, and rheological properties of WL before and after alkali treatment were compared systematically. FTIR, NMR, and zeta potential results indicate that the alkali causes acetyl group hydrolysis and carboxyl group deprotonation. XRD, DLS, GPC, and AFM results suggest that the alkali destroys the ordered arrangement and inter- and intrachain entanglement of polysaccharide chains. In the same case, 0.9 M NaOH-treated WL presents better solubility (stirring for 15 min to obtain a clarified solution) but, unsurprisingly, worsens rheological properties. All results demonstrated that the good solubility and transparency of alkali-treated WL will help promote its postmodification and application.

Cost-Efficient Production of the Sphingan WL Gum by Sphingomonas sp. WG Using Molasses and Sucrose as the Carbon Sources

The polysaccharide WL gum is produced by the marine microorganism Sphingomonas sp. WG and presents great commercial utility potential in many industries especially in oil industries. However, the high fermentation cost limits its wide application. Therefore, an efficient production system at a lower cost was established using beet molasses to partially replace the commonly used carbon sources. Four different molasses were screened and their composition was investigated. One-factor design and RSM statistical analysis were employed to optimize the WL gum fermentation medium. The effects of molasses on the rheological properties and gene expression of WL gum were also investigated. The results showed that the pretreated beet molasses generated both high broth viscosity and WL gum production (12.94 Pa·s and 11.16 g/L). Heavy metal ions and ash were found to be the key factors in unpretreated and pretreated molasses affecting WL production. The cost-efficient production medium contained (g/L): sucrose 61.79, molasses 9.95, yeast extract 1.23, K₂HPO₄ 1, MgSO₄ 0.1, ZnSO₄ 0.1 and the WL gum production reached 40.25 ± 1.15 g/L. The WL gum product WL-molasses showed the higher apparent viscosity, and viscous modulus and elastic modulus than WL-sucrose and WL-mix, which might be related to its highest molecular mass. The higher expressional level of genes such as pgm, ugp, ugd, rmlA, welS, and welG in WL gum synthesis in the mixed carbon source medium caused the high production and broth viscosity. This work provided a cost-efficient method for WL gum production.

Effect of the Welan Gum Concentration on the Rheological and Structural Behaviour of Biocomposite Hydrogels with Sepiolite as Filler

A very positive and effective approach to tuning the mechanical properties of polymers has been the development of composites. This paper deals with novel biocomposite hydrogels composed by two biocompatible materials: welan gum as biopolymer matrix and sepiolite as filler. Welan gum content was studied as a tuning parameter to control the rheological properties of the developed biocomposites. The rheological and microstructural behaviour of the composites was investigated by mean of steady-state flow curves, creep-recovery tests, small amplitude oscillatory shear tests, and electron microscopy. An increase in welan gum content provoked the progressive disappearance of the shear-thinningzero-shear-thinning behaviour with a yield point which was clearly defined, characteristic of sepiolite gels, leading to a conventional shear-thinning behaviour, typical of polymeric systems. Also, a higher content of biopolymer in the mixtures led to a more elastic and compact structure characterized by higher values of both G' and G". The fundamental novelty was based on taking the flowability provided by the biopolymer as the main objective and reinforcing the viscosity yielded by welan gum with sepiolite, which contributed to increasing the biocomposite consistency. Thus, rheological properties can be adjusted, taking into account the balance of the components to adapt them to the requirements of each application.

Enzymatic degradation, antioxidant and rheological properties of a sphingan WL gum from Sphingomonas sp. WG

A molecular weight (Mw) controllable degradation strategy using the lyase WelR as the efficient tool was established, and the relationship between the Mw and the rheological properties and antioxidant activity of WL gum was systematically investigated. Four different WL samples WL1-WL4 with a gradient Mw change (from 4.70 × 10⁶ to 1.45 × 10⁶ Da) were obtained by controlling the enzymatic reaction conditions. As the Mw decreased, its apparent viscosity, intrinsic viscosity, viscous modulus (G″) and elastic modulus (G') decreased. More interestingly, in contrast to the native WL, the G″ of the degraded WL became higher than G'. Besides, the biodegraded WL samples possessed much higher hydroxyl radicals scavenging activity than the original WL. WL4 with the lowest Mw showed the highest HO radical scavenging activity, about 94.65% at 1 mg/mL. This work provided a useful method to obtain a series of WL samples with controllable Mw and properties, which will broaden the application of sphingans.

Application of Polymers for Chemical Enhanced Oil Recovery: A Review

Polymers play a significant role in enhanced oil recovery (EOR) due to their viscoelastic properties and macromolecular structure. Herein, the mechanisms of the application of polymeric materials for enhanced oil recovery are elucidated. Subsequently, the polymer types used for EOR, namely synthetic polymers and natural polymers (biopolymers), and their properties are discussed. Moreover, the numerous applications for EOR such as polymer flooding, polymer foam flooding, alkali–polymer flooding, surfactant–polymer flooding, alkali–surfactant–polymer flooding, and polymeric nanofluid flooding are appraised and evaluated. Most of the polymers exhibit pseudoplastic behavior in the presence of shear forces. The biopolymers exhibit better salt tolerance and thermal stability but are susceptible to plugging and biodegradation. As for associative synthetic polyacrylamide, several complexities are involved in unlocking its full potential. Hence, hydrolyzed polyacrylamide remains the most coveted polymer for field application of polymer floods. Finally, alkali–surfactant–polymer flooding shows good efficiency at pilot and field scales, while a recently devised polymeric nanofluid shows good potential for field application of polymer flooding for EOR.

Characterization of a polysaccharide hydrogel with high elasticity produced by a mutant strain Sphingomonas sanxanigenens NX03

Microbial polysaccharides as renewable bioproducts have attracted lots of attention in various industries. Hesan (Highly elastic Sanxan), an exopolysaccharide produced by a plasma mutagenic strain Sphingomonas sanxanigenens NX03, was characterized. It possessed the same monosaccharide composition as the original polysaccharide Sanxan produced from wild-type strain NX02, but significantly reduced acetyl and glyceryl contents. Textural analysis showed the springiness and cohesiveness of Hesan gel was much higher than Sanxan gel, and rheological behaviors indicated it possessed a lower loss factor, and its conformational transition temperatures at different concentrations were obviously lower than Sanxan gel and high-acyl gellan gel, which suggested that Hesan gel was highly elastic and temperature-sensitive. Additionally, Hesan gel could be efficiently produced through micro-aerobic static culture in shallow (10.46 ± 0.30 g/L) and deep liquids (3.21 ± 0.32 g/L), which was significantly different from the fermentation of other water-soluble polysaccharides. In short, this study characterizes a new mutant strain and its polysaccharide products.

Evidence from Thermal Aging Indicating That the Synergistic Effect of Glyoxal and Sodium Sulfite Improved the Thermal Stability of Conformational Modified Xanthan Gum

Xanthan gum is prone to thermal oxidative degradation, which limits its applications. However, conformational changes in xanthan gum and appropriate stabilizers may improve its thermal stability. Therefore, in this study, we aimed to establish a strategy to maintain the viscosity of xanthan gum during long-term storage at high temperatures. We modified the original strain used for xanthan gum production by genetic engineering and added stabilizers during the production process. The structure and thermal stability of the resulting xanthan gum samples were then determined. Pyruvyl deficiency, combined with the addition of sodium sulfite and glyoxal during the production process, was found to significantly improve the maintenance of viscosity. The apparent viscosity of the new xanthan gum solution remained above 100 mPa·s after being stored at 90 °C for 48 days. Fourier-transform infrared spectra and scanning electron microscopy images showed that pyruvate-free xanthan gum with added stabilizers had more extensive cross-linking than natural xanthan gum. In conclusion, these findings may contribute to the use of xanthan gum in applications that require high temperatures for a long period of time.

Weilan gum oligosaccharide ameliorates dextran sulfate sodium‑induced experimental ulcerative colitis

Ulcerative colitis (UC) is a global disease, characterized by periods of relapse that seriously affects the quality of life of patients. Oligosaccharides are considered to be a prospective strategy to alleviate the symptoms of UC. The present study aimed to evaluate the effect of weilan gum oligosaccharide (WLGO) on a mouse UC model induced by dextran sulfate sodium (DSS). WLGO structural physical properties were characterized by electrospray mass spectrometry and fourier tansform infrared spectroscopy. MTT assays were performed to evaluate the non‑toxic concentration of WLGO. RT‑qPCR and ELISAs were conducted to determine the levels of inflammatory factors. The clinical symptoms and mucosal integrity of the DSS‑induced UC model were assessed by DAI and histological assessment. LPS‑induced Caco‑2 cells and DSS‑induced UC mice were used to explore the effects of WLGO on UC. Treatment of the mice with 4.48 g/kg/day WLGO via gavage for 7 days significantly relieved the symptoms of DSS‑induced UC model mice, whereas significant effects were not observed for all symptoms of DSS‑induced UC in the WLGO‑low group. The disease activity index score was decreased and the loss of body weight was reduced in DSS‑induced UC model mice treated with WLGO. Moreover, colonic damage and abnormally short colon length shortenings were relieved following WLGO treatment. WLGO treatment also reduced the concentration and mRNA expression levels of proinflammatory cytokines, including interleukin‑1β, interleukin‑6 and tumor necrosis factor α, in DSS‑induced UC model mice and lipopolysaccharide‑treated Caco‑2 cells. These results indicated that WLGO may be an effective strategy for UC treatment.

Food wastes as natural sources of lactic acid bacterial exopolysaccharides for the functional food industry: A review

Exopolysaccharides (EPSs) synthesized by lactic acid bacteria (LAB), have recently received much interest because of their various functional features in several industries. Food wastes (FWs) have become a major source of worry, as they can cause serious environmental contamination if improperly disposed. The utilization of these FWs is an excellent choice (approach) for producing value-added products such as EPSs, which will efficiently remediate wastes. The overall EPSs yield for the selected producers is strain-specific, and is heavily influenced by the nutritional and growing conditions used. This review emphasizes what is currently known about LAB's ability to generate economically relevant EPSs from FWs. In addition, a concise overview of the food industry, packaging, pharmaceutical and clinical applications application is discussed.

Water-soluble polymers in agriculture: xanthan gum as eco-friendly alternative to synthetics

Water-soluble polymers (WSPs) are a versatile group of chemicals used across industries for different purposes such as thickening, stabilizing, adhesion and gelation. Synthetic polymers have tailored characteristics and are chemically homogeneous, whereas plant-derived biopolymers vary more widely in their specifications and are chemically heterogeneous. Between both sources, microbial polysaccharides are an advantageous compromise. They combine naturalness with defined material properties, precisely controlled by optimizing strain selection, fermentation operational parameters and downstream processes. The relevance of such bio-based and biodegradable materials is rising due to increasing environmental awareness of consumers and a tightening regulatory framework, causing both solid and water-soluble synthetic polymers, also termed 'microplastics', to have come under scrutiny. Xanthan gum is the most important microbial polysaccharide in terms of production volume and diversity of applications, and available as different grades with specific properties. In this review, we will focus on the applicability of xanthan gum in agriculture (drift control, encapsulation and soil improvement), considering its potential to replace traditionally used synthetic WSPs. As a spray adjuvant, xanthan gum prevents the formation of driftable fine droplets and shows particular resistance to mechanical shear. Xanthan gum as a component in encapsulated formulations modifies release properties or provides additional protection to encapsulated agents. In geotechnical engineering, soil amended with xanthan gum has proven to increase water retention, reduce water evaporation, percolation and soil erosion - topics of high relevance in the agriculture of the 21st century. Finally, hands-on formulation tips are provided to facilitate exploiting the full potential of xanthan gum in diverse agricultural applications and thus providing sustainable solutions.

Rediscovering bacterial exopolysaccharides of terrestrial and marine origins: novel insights on their distribution, biosynthesis, biotechnological production, and future perspectives

Bacteria exist in colonies as aggregates or associated with surfaces forming biofilms rather than planktonic cells. Living in such a unique manner is always mediated via a matrix of extracellular polymeric substances, which are composed mainly of polysaccharides or specifically exopolysaccharides (EPS). Biofilm formation and hence EPS production are affected by biotic and abiotic factors inducing/inhibiting several involved genes and other molecules. In addition, various aspects of bacterial EPS regarding: physiological functions, molecular weight, and chemical composition were demonstrated. Recent investigations have revealed a wide spectrum of EPS chemical and physicochemical properties showing promising applications in different industrial sectors. For instance, lactic acid bacteria (LAB)- and marine-derived EPS exhibit: immunomodulatory, antioxidant, antitumor, bioremediation of heavy metals, as well as thickening and viscosity modifiers in the food industry. However, bacterial EPS have not yet been commercially implemented, in contrast to plant-derived analogues. The current review aims to rediscover the EPS structural and biosynthetic features derived from marine and terrestrial bacteria, and applications as well.

Bacterial exopolysaccharides for improvement of technological, functional and rheological properties of yoghurt

Exopolysaccharides (EPS) are known to have technological and functional applications in food industry including dairy based products such as yoghurt. Yoghurt is a widely consumed dairy based product due to pleasant taste and texture, as well as a source of nutrients and bioactive compounds. At the same time, structural, rheological and sensorial properties are important in the production of good quality yoghurt. Various natural hydrocolloids including EPS with stabilizing and texture enhancing properties could be useful in enhancing these desirable properties. Apart from that, EPS may enhance various other functional properties of yoghurt such as antioxidant and prebiotic potential. Based on its prebiotic property, symbiotic products could be developed by combining EPS and probiotic bacterial strains. EPS has potential to provide physical and micro structural stability, thereby enhancing the protein distribution and viscoelastic properties. Main focus of the present review is to provide an insight on the action of EPS as a functional hydrocolloid on the technological, rheological and functional properties of yoghurt and related products.

Cell-based high-throughput screening of polysaccharide biosynthesis hosts

Valuable polysaccharides are usually produced using wild-type or metabolically-engineered host microbial strains through fermentation. These hosts act as cell factories that convert carbohydrates, such as monosaccharides or starch, into bioactive polysaccharides. It is desirable to develop effective in vivo high-throughput approaches to screen cells that display high-level synthesis of the desired polysaccharides. Uses of single or dual fluorophore labeling, fluorescence quenching, or biosensors are effective strategies for cell sorting of a library that can be applied during the domestication of industrial engineered strains and metabolic pathway optimization of polysaccharide synthesis in engineered cells. Meanwhile, high-throughput screening strategies using each individual whole cell as a sorting section are playing growing roles in the discovery and directed evolution of enzymes involved in polysaccharide biosynthesis, such as glycosyltransferases. These enzymes and their mutants are in high demand as tool catalysts for synthesis of saccharides in vitro and in vivo. This review provides an introduction to the methodologies of using cell-based high-throughput screening for desired polysaccharide-biosynthesizing cells, followed by a brief discussion of potential applications of these approaches in glycoengineering.

A strategy for the synthesis of low-molecular-weight welan gum by eliminating capsule form of Sphingomonas strains

Welan gum is widely used in food, concrete additives, and oil recovery. Here we changed the capsule form of Sphingomonas strains by knocked out the sortase gene (srtW). The obtained welan gum was mainly composed of mannose, glucose, rhamnose, and glucuronic acid at a molar ratio of 4.0:5.8:1.6:1, respectively. Meanwhile, the molecular weight of welan gum decreased sharply (about 68 kDa). Moreover, the low molecular weight (LMW) welan gum was characterized by FT-IR and NMR spectroscopy. The rheological results revealed that the LMW welan gum solution is a pseudoplastic fluid with a lower apparent viscosity. Furthermore, the oscillation test illustrated stable dynamic viscoelasticity within the temperature range of 5-68 °C and frequency range of 0.01-15 rad/s. To the best of our knowledge, this is the first report of LMW welan gum production and characterization. These results provide references for LMW welan gum applications, and likely applicable for other biopolymers production.

Biosurfactants and Their Applications in the Oil and Gas Industry: Current State of Knowledge and Future Perspectives

Surfactants are a group of amphiphilic chemical compounds (i.e., having both hydrophobic and hydrophilic domains) that form an indispensable component in almost every sector of modern industry. Their significance is evidenced from the enormous volumes that are used and wide diversity of applications they are used in, ranging from food and beverage, agriculture, public health, healthcare/medicine, textiles, and bioremediation. A major drive in recent decades has been toward the discovery of surfactants from biological/natural sources-namely bio-surfactants-as most surfactants that are used today for industrial applications are synthetically-manufactured via organo-chemical synthesis using petrochemicals as precursors. This is problematic, not only because they are derived from non-renewable resources, but also because of their environmental incompatibility and potential toxicological effects to humans and other organisms. This is timely as one of today's key challenges is to reduce our reliance on fossil fuels (oil, coal, gas) and to move toward using renewable and sustainable sources. Considering the enormous genetic diversity that microorganisms possess, they offer considerable promise in producing novel types of biosurfactants for replacing those that are produced from organo-chemical synthesis, and the marine environment offers enormous potential in this respect. In this review, we begin with an overview of the different types of microbial-produced biosurfactants and their applications. The remainder of this review discusses the current state of knowledge and trends in the usage of biosurfactants by the Oil and Gas industry for enhancing oil recovery from exhausted oil fields and as dispersants for combatting oil spills.

Efficient simultaneous utilization of glucose and xylose from corn straw by Sphingomonas sanxanigenens NX02 to produce microbial exopolysaccharide

Lignocellulosic biomass is a cheap and abundant carbon source in the microbial manufacturing industry. The native co-utilization of glucose and xylose from corn straw total hydrolysate (CSTH) by Sphingomonas sanxanigenens NX02 to produce exopolysaccharide Sanxan was investigated. Batch fermentation demonstrated that, compared to single sugar fermentation, co-substrate of glucose and xylose accelerated cell growth and Sanxan production in the initial 24 h with the same consumption rate. Additionally, NX02 converted CSTH into Sanxan with a yield of 13.10 ± 0.35 g/Kg, which is slightly higher than that of glucose fermentation. Coexistence of three xylose metabolic pathways (Xylose isomerase, Weimberg, and Dahms pathway), incomplete phosphoenolpyruvate-dependent phosphotransferase system, and reinforced fructose metabolism were recognized as the co-utilization mechanism through comparative transcriptome analysis. Therefore, strain NX02 has a prospect of becoming an attractive platform organism to produce polysaccharides and other bio-based products derived from agricultural waste hydrolysate rich in both glucose and xylose.

Welan gum promoted the growth of rice seedlings by enhancing carbon and nitrogen assimilation

Based on the characteristics of natural polysaccharides in film-forming, chelating, and environmental friendly, a natural polysaccharide fertilizer agent was selected to increase the utilization of nitrogen fertilizer and increase plant growth. Five polysaccharides: xanthan gum, guar gum, fenugreek gum, welan gum and chitosan were screened for plant growth promoting effect. The results showed that welan gum had the most significant effect on promoting the growth of rice seedlings, and the concentrations of 0.1 mg mL^-1 and 0.15 mg mL^-1 showed the best growth effects. The effects of welan gum on nitrogen utilization in rice seedlings were investigated. Results showed welan gum increased the contents of ammonium, nitrate, free amino acids, and proteins in rice seedlings. There were four key enzymes of nitrogen metabolism which are nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase significantly enhanced by welan gum though up-regulating the transcriptional levels of these enzymes. Therefore, nitrogen uptake and nitrogen metabolism in rice seedlings were promoted to increase the biomass of rice seedlings. Based on the research, results showed that welan gum could constitute a promising fertilizer in the future.

Rheological behaviors of a novel exopolysaccharide produced by Sphingomonas WG and the potential application in enhanced oil recovery

A novel exopolysaccharide, named WL gum, was obtained from the fermentation broth of Sphingomonas sp. WG. The effects of temperature and salinity on the rheological properties of WL gum solution and fermentation broth (WL-Fer) were systematically investigated and compared with another exopolysaccharide, welan gum (WG). The results showed that the network structures formed in WL solution were more compact than those of WG. WL solution and WL-Fer were not sensitive to high temperatures (80-120 °C) and only weakly affected by the cations (Na⁺, K⁺, and Ca²⁺). Moreover, Fe²⁺ and high temperature (100 °C) even enhanced the viscosity of WL-Fer. The results of flooding experiments demonstrated that the enhanced displacement efficiency of WL gum (14.55%) was similar to that of partially hydrolyzed polyacrylamide (HPAM, 13.36%) at 65 °C. And the enhanced displacement efficiency of WL-Fer was as high as 23.31%. It can be concluded that WL gum is a kind of potential and environmentally benign polymer that could be used in EOR, and the fermentation broth could be used directly after dilution.

Sphingomonas palmae sp. nov. and Sphingomonas gellani sp. nov., endophytically associated phyllosphere bacteria isolated from economically important crop plants

In this study, two endophytic bacterial strains designated JS21-1^T and S6-262^T isolated from leaves of Elaeis guineensis and stem tissues of Jatropha curcas respectively, were subjected for polyphasic taxonomic approach. On R2A medium, colonies of strains JS21-1^T and S6-262^T are orange and yellow, respectively. Phylogenetic analyses using 16S rRNA gene sequencing and whole-genome sequences placed the strains in distinct clades but within the genus Sphingomonas. The DNA G + C content of JS21-1^T and S6-262^T were 67.31 and 66.95%, respectively. Furthermore, the average nucleotide identity and digital DNA-DNA hybridization values of strains JS21-1^T and S6-262^T with phylogenetically related Sphingomonas species were lower than 95% and 70% respectively. The chemotaxonomic studies indicated that the major cellular fatty acids of the strain JS21-1^T were summed feature 8 (C_18:1 ω7c and/or C_18:1 ω6c), C_16:0, and C_14:0 2OH; strain S6-262^T possessed summed feature 3 (C_16:1 ω7c and/or iso-C_15:0 2-OH) and summed feature 8 (C_18:1 ω6c and/or C_18:1 ω7c). The major quinone was Q10, and the unique polyamine observed was homospermidine. The polar lipid profile comprised of mixture of sphingoglycolipid, phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol and certain uncharacterised phospholipids and lipids. Based on this polyphasic evidence, strains JS21-1^T and S6-262^T represent two novel species of the genus Sphingomonas, for which the names Sphingomonas palmae sp. nov. and Sphingomonas gellani sp. nov. are proposed, respectively. The type strain of Sphingomonas palmae sp. nov. is JS21-1^T (= DSM 27348^T = KACC 17591^T) and the type strain of Sphingomonas gellani sp. nov. is S6-262^T (= DSM 27346^T =  KACC 17594^T).

Efficient biosynthesis of polysaccharide welan gum in heat shock protein-overproducing Sphingomonas sp. via temperature-dependent strategy

Cell growth and product formation are two critical processes in polysaccharide welan biosynthesis, but the conflict between them is often encountered. In this study, a temperature-dependent strategy was designed for two-stage welan production through overexpressing heat shock proteins in Sphingomonas sp. The first stage was cell growth phase with higher TCA cycle activity at 42 °C; the second stage was welan formation phase with higher precursor synthesis pathway activity at 37 °C. The highest welan concentration 37.5 g/L was achieved after two-stage process. Ultimately, this strategy accumulated welan yield of 79.2 g/100 g glucose and productivity of 0.62 g/L/h at 60 h, which were the best reported results so far. The duration of fermentation was shortened. Besides, rheological behavior of welan gum solutions remained stable at wide range of temperature, pH, and NaCl. These results indicated that this approach efficiently improved welan synthesis.

Characterization of novel nanoemulsions, with improved properties, based on rosemary essential oil and biopolymers

BACKGROUND

Nowadays, it is of great interest to develop stable and sustainable formulations that act as nanocarriers of active ingredients. In this work, the droplet size distribution, rheology and physical stability of nanoemulsions with improved properties containing rosemary essential oil and biopolymers as a function of the concentration of these polysaccharides were investigated.

RESULTS

Mean diameters below 150 nm were achieved, indicating nanostructures were obtained. Regardless of gum type, a gel-like structure and a shear thinning behaviour was achieved. In addition, an increase of G', G″ and viscosity and a decrease of J₀ , J₁ , J₂ , λ₁ and λ₂ with increasing gum concentration were observed, due to the formation of a three-dimensional network in the aqueous phase. Slight differences between nanoemulsions containing welan or xanthan were found. Creaming, depletion flocculation and gel aggregation were the main destabilization processes at low, intermediate and high gum concentration, respectively. A 0.4 wt% gum nanoemulsion exhibited the best physical stability.

CONCLUSION

These stable and sustainable nanoemulsions with improved rheological properties contribute to the development of biodegradable and non-toxic food or agrochemical products. © 2020 Society of Chemical Industry.

Recent Advances in Natural Gum-Based Biomaterials for Tissue Engineering and Regenerative Medicine: A Review

The engineering of tissues under a three-dimensional (3D) microenvironment is a great challenge and needs a suitable supporting biomaterial-based scaffold that may facilitate cell attachment, spreading, proliferation, migration, and differentiation for proper tissue regeneration or organ reconstruction. Polysaccharides as natural polymers promise great potential in the preparation of a three-dimensional artificial extracellular matrix (ECM) (i.e., hydrogel) via various processing methods and conditions. Natural polymers, especially gums, based upon hydrogel systems, provide similarities largely with the native ECM and excellent biological response. Here, we review the origin and physico-chemical characteristics of potentially used natural gums. In addition, various forms of scaffolds (e.g., nanofibrous, 3D printed-constructs) based on gums and their efficacy in 3D cell culture and various tissue regenerations such as bone, osteoarthritis and cartilage, skin/wound, retinal, neural, and other tissues are discussed. Finally, the advantages and limitations of natural gums are precisely described for future perspectives in tissue engineering and regenerative medicine in the concluding remarks.

Current status of biotechnological production and applications of microbial exopolysaccharides

Microbial exopolysaccharides (EPS) are an abundant and important group of compounds that can be secreted by bacteria, fungi and algae. The biotechnological production of these substances represents a faster alternative when compared to chemical and plant-derived production with the possibility of using industrial wastes as substrates, a feasible strategy after a comprehensive study of factors that may affect the synthesis by the chosen microorganism and desirable final product. Another possible difficulty could be the extraction and purification methods, a crucial part of the production of microbial polysaccharides, since different methods should be adopted. In this sense, this review aims to present the biotechnological production of microbial exopolysaccharides, exploring the production steps, optimization processes and current applications of these relevant bioproducts.