Improvement in Production and Quality of Gellan Gum by Sphingomonas paucimobilis Under High Dissolved Oxygen Tension Levels

Challenges and opportunities in bioprocessing of gellan gum: A review

Gellan gum (GG) - the microbial exopolysaccharide is increasingly being adopted into drug development, tissue engineering, and food and pharmaceutical products. In spite of the commercial importance and expanding application horizon of GG, little attention has been directed toward the exploration of novel microbial cultures, development of advanced screening protocols, strain engineering, and robust upstream or downstream processes. This comprehensive review not only attempts to summarize the existing knowledge pool on GG bioprocess but also critically assesses their inherent challenges. The process optimization design augmented with advanced machine learning modeling tools, widely adopted in other microbial bioprocesses, should be extended to GG. The unification of mechanistic insight into data-driven modeling would help to formulate optimal feeding and process control strategies.

Mutagenesis enhances gellan gum production by a novel Sphingomonas spp.: upstream optimization, kinetic modeling, and structural and physico-functional evaluation

Gellan gum (GG) has gained tremendous attention owing to its diversified applications. However, its high production and hence market cost are still a bottleneck in its widespread utilization. In the present study, high GG producing mutant of Sphingomonas spp. was developed by random mutagenesis using ethyl methylsulphonate (EMS) for industrial fermentation and identified as Sphingomonas trueperi after 16S rRNA and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS) analysis. The fermentation conditions such as pH, temperature, and inoculum ratio were optimized by one factor at a time (OFAT) followed by screening of medium components by the Plackett-Burman statistical design. The most critical nutrients were further optimized by response surface methodology for maximizing GG production. The effect of dissolved oxygen tension in bioreactor on cell growth, substrate consumption, GG production, and batch productivity was elucidated. The highest GG titer (23 ± 2.4 g/L) was attained in optimized medium at 10% inoculum (6.45 ± 0.5 log cfu/mL) under controlled fermentation conditions of pH (7), temperature (30 °C), agitation (300-600 rpm), and aeration (0.5-2.0 SLPM) at 22 ± 2% dissolved oxygen tension in a 10-L bioreactor. Kinetic modeling of optimized batch process revealed that logistic growth model could best explain biomass accumulation, while GG formation and substrate consumption were best explained by Luedeking-Piret and exponential decay model, respectively. Structural and physico-functional features of GG produced by mutant Sphingomonas spp. were characterized by HPLC, FTIR, NMR, DSC, TGA, GPC, SEM, and rheological analysis. The higher productivity (0.51 g/L/h) under optimized fermentation conditions suggests potential consideration of mutant and process for commercial utilization.

Advances in fermentative production, purification, characterization and applications of gellan gum

Multiple microbial exopolysaccharides have been reported in recent decade with their structural and functional features. Gellan gum (GG) is among these emerging biopolymers with versatile properties. Low production yield, high downstream cost, and abundant market demand have made GG a high cost material. Hence, an understanding on the various possibilities to develop cost-effective gellan gum bioprocess is desirable. This review focuses on details of upstream and downstream process of GG from an industrial perspective. It emphasizes on GG producing Sphingomonas spp., updates on biosynthesis, strain and media engineering, kinetic modeling, bioreactor design and scale-up considerations. Details of the downstream operations with possible modifications to make it cost-effective and environmentally sustainable have been discussed. The updated regulatory criteria for GG as a food ingredient and analytical tools required to validate the same have been briefly discussed. Derivatives of GG and their applications in various industrial segments have also been highlighted.

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.

Synthesis of the Microbial Polysaccharide Gellan from Dairy and Plant-Based Processing Coproducts

This review examines the production of the microbial polysaccharide gellan, synthesized by Sphingomonas elodea, on dairy and plant-based processing coproducts. Gellan is a water-soluble gum that structurally exists as a tetrasaccharide comprised of 20% glucuronic acid, 60% glucose and 20% rhamnose, for which various food, non-food and biomedical applications have been reported. A number of carbon and nitrogen sources have been tested to determine whether they can support bacterial gellan production, with several studies attempting to optimize gellan production by varying the culture conditions. The genetics of the biosynthesis of gellan has been explored in a number of investigations and specific genes have been identified that encode the enzymes responsible for the synthesis of this polysaccharide. Genetic mutants exhibiting overproduction of gellan have also been identified and characterized. Several dairy and plant-based processing coproducts have been screened to learn whether they can support the production of gellan in an attempt to lower the cost of synthesizing the microbial polysaccharide. Of the processing coproducts explored, soluble starch as a carbon source supported the highest gellan production by S. elodea grown at 30 °C. The corn processing coproducts corn steep liquor or condensed distillers solubles appear to be effective nitrogen sources for gellan production. It was concluded that further research on producing gellan using a combination of processing coproducts could be an effective solution in lowering its overall production costs.

The preparation and characterization of a novel sphingan WL from marine Sphingomonas sp. WG

Sphingans, a group of structurally closely related bacterial exopolysaccharides produced by members of the genus Sphingomonas, can be applied in a variety of industries such as food, cement, and personal care applications due to their high viscosity. A high sphingan-producing-bacterium, Sphingomonas sp. WG can secret large quantity of sphingan designated as WL. To enhance the production of WL, a three-stage control strategy was applied and the highest WL production can reach 33.3 g/L. The rheological analysis showed that the aqueous solution of WL had high viscosity, typical shearing-thinning behavior and great stability to high temperature, a wide range of pH (1 to 14), and high salinity. WL was composed principally of carbohydrate with 6.52% O-acyl groups. The carbohydrate portion of WL contained about 13% glucuronic acid and some neutral sugars including mannose, glucose and rhamnose in the molar ratio of 1:2.28:2.12. Partial acid hydrolysis of WL produced a new oligosaccharide WL-1. Structural resolution revealed that WL-1 consisted of α-L-Rha-(1→4)-β-L-Rha-(1→4)-β-D-Glc-(1→3)-α-D-Glc with β-D-Man substituent at the third glucose residue and carboxyl and O-acyl groups. These findings will broaden the applications of this novel sphingan in food, ink, oil and other industries.

Avoiding hepatic metastasis naturally: Lessons from the cotton top tamarin (Saguinus oedipus)

Much has been written about hepatic metastasis and animal models abound. In terms of the human experience, progress in treating this final common pathway, a terminal event of many human malignancies has been relatively slow. The current thinking is that primary prevention is best served by early detection of cancer and eradication of early stage cancers by screening. Some cancers spread early in their course and the role of screening may be limited. Until relatively recently there has not been a pathfinder model that makes the evasion of this unfortunate event a reality. This review discusses such an animal model and attempts to relate it to human disease in terms of intervention. Concrete proposals are also offered on how scientists may be able to intervene to prevent this deadly progression of the cancer process.

Oscillatory and steady shear rheology of gellan/dextran blends

Oscillatory and steady shear rheology of gellan (G) and dextran (D) solution individually, and in blends (G/D ratio 1:1, 1:2, and 1:3 w/v) with a total hydrocolloid concentration of 3 % (w/v) were studied at 25 °C. Individually, 1.5 % dextran and 1.5 % gellan in solution exhibited Newtonian and non-Newtonian behavior, respectively. A blend of equal proportion of dextran and gellan (G/D = 1:1) exhibits a distinct gel point (G' = G″), and further addition of dextran in the blend (G/D = 1:2 and 1:3) resulted predominating liquid-like (G″ > G') behavior. A plot of G' vs G″ distinctly showed the gradual transition of the blend. Shear stress (τ)-shear rate ([Formula: see text]) data fitted well the Herschel-Bulkley model. The G/D blend exhibited shear thinning behavior with flow behavior index less than unity. The Cox-Merz rule did not fit well for the complex shear viscosity (η*) and apparent viscosity (η) of the blend.

Rhamsan gum production by Sphingomonas sp. CGMCC 6833 using a two-stage agitation speed control strategy

Varying the agitation speed could greatly affect rhamsan gum production by Sphingomonas sp. CGMCC 6833. Batch fermentations at agitation speeds of 400, 600, 800, and 1,000 rpm were therefore carried out. The time course of specific cell growth rate, specific glucose consumption rate, and specific rhamsan gum formation rate was subsequently determined. Based on the results, a novel two-stage agitation speed control strategy was developed. From 0 to 13 H, the high specific cell growth and glucose consumption rates were achieved by setting the agitation speed of the fermenter at 800 rpm. From 13 H onward to the end of fermentation, the glucose consumption rate and specific cell growth rate were high at the agitation speed of 600 rpm. Using this method, the maximum concentration and productivity of rhamsan gum reached 21.63 ± 1.76 g L(-1) and 0.338 ± 0.028 g L(-1)  H(-1) , respectively, which were both higher than the optimum results obtained at constant agitation speeds.

A new strategy to enhance gellan production by two-stage culture in Sphingomonas paucimobilis

The effects of different initial sucrose concentrations and temperatures on gellan biosynthesis by Sphingomonas paucimobilis ATCC 31461 were investigated. Lower sucrose concentrations and higher temperatures were favorable for cell growth. Higher sucrose concentrations and lower temperatures promoted gellan production but retarded cell growth. Based on these results, a two-stage culture strategy was developed to improve gellan production. During the first 24 h, S. paucimobilis was cultured in a pulse fed-batch mode with an initial sucrose concentration 10 g/L. Ten grams per liter of sucrose were added at 12 h and 24 h, and the temperature was controlled at 33 °C. Batch culture was performed, and the temperature was reduced to 28 °C to achieve a high gellan accumulation. The two-stage culture strategy achieved the highest gellan production (22.61 g/L) at 60 h that was 35.71% higher than the result of the best conventional batch operation (16.66 g/L). Meanwhile, high gellan yield was related to high UDPG-pyrophosphorylase activity and glucosyltransferase activity.

Bi-stage control of dissolved oxygen to enhance cyclic adenosine monophosphate production by Arthrobacter A302

Experiments confirmed dissolved oxygen (DO) definitely affects cyclic adenosine monophosphate (cAMP) production by Arthrobacter A302. Production of cAMP by batch fermentation was investigated under various DO conditions. A two-stage DO control strategy was proposed to achieve optimal production of cAMP based on the kinetic analysis: the DO level was controlled at 40% during the first 18 h and then switched to 30%. Relatively high cAMP production (9.9 g L(-1)) was achieved by applying this strategy. The cAMP productivity (0.14 g L(-1) h(-1)) was also successfully improved by 85.1, 59.3, 15.1 and 28.0%, compared to cases in which DO was uncontrolled or DO levels were held at 20, 30 and 40%, respectively. This is the first report of the use of a two-stage DO control strategy in cAMP production, and it was verified to be an effective method for enhancing the cAMP yield via this strain.