Enhanced gellan gum production by hydrogen peroxide (H2O2) induced oxidative stresses in Sphingomonas paucimobilis

Effects of fermentation conditions on molecular weight, production, and physicochemical properties of gellan gum

Gellan gum has been widely used in many industries due to its excellent physical properties. In this study, the effects of different fermentation conditions on molecular weight and production of gellan gum were analyzed, and the optimized fermentation conditions for a high molecular weight gellan gum (H-GG: 6.42 × 105 Da) were obtained, which increased the molecular weight and yield of gellan gum by 201.4 % and 44.9 % respectively. Fourier transform infrared spectroscopy (FT-IR) and x-ray diffraction (XRD) analysis indicated that H-GG has similar characteristic absorption and semi-crystalline structures with the initial gellan gum (I-GG), and it was composed of glucose, rhamnose, and glucuronic acid showing no obvious changes in the molecular structure. Scanning electron microscope (SEM) observation revealed that the filaments of H-GG were slender, longer, and looser with larger pores. Importantly, gel properties analysis showed that the gel strength, viscoelasticity, and water-holding capacity of H-GG were better than those of I-GG, and the rheological results revealed that the H-GG is a pseudoplastic fluid with higher apparent viscosity and stable viscoelasticity at 20-70 °C. Therefore, the molecular weight and yield of gellan gum are significantly affected by fermentation conditions, and the obtained H-GG demonstrates improved gel and rheological properties.

Effect of NaCl addition on the production of welan gum with the UV mutant of Sphingomonas sp

Because of its excellent stability, non-toxicity, biodegradability and unique rheology, welan gum can be widely used in various fields, such as petroleum, biomedicine and food products. In this study, a high-yield mutant strain FM01-S09 was screened through two rounds of UV mutagenesis. Remarkably, the production of welan gum could be further increased by adding 4 mM NaCl at 32 h fermentation, reaching 30.12 ± 0.25 g/L (28.66% higher than no adding), and the NaCl-WG solution had stronger structural, impact resistance, and temperature resistance than H₂O₂-WG and WG solutions. Furthermore, the mechanism by which NaCl promotes welan gum synthesis was also investigated. It was found that cell membrane characteristics, intracellular microenvironment makeup, and key enzyme gene expression levels were significantly altered in different fermentation stages. Therefore, the addition of NaCl could effectively promote the growth and fermentation performance of Sphingomonas sp., providing a novel strategy for cost-effective welan gum production.

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.

Effect of 2-deoxy-D-glucose on gellan gum biosynthesis by Sphingomonas paucimobilis

2-Deoxy-D-glucose (2-DG) is a non-metabolizable glucose analogue and competitive inhibitor of glycolysis. Effect of 2-DG on gellan gum biosynthesis by Sphingomonas paucimobilis ATCC31461 were studied in this research. The concentration and the addition time of 2-DG significantly affected the biomass and gellan gum accumulation. The maximum gellan gum yield of 20.78 g/L was obtained with the addition of 50 µg/L of 2-DG at 24 h. The mechanism of 2-DG addition favoring to gellan production was revealed by determining the activities of key enzymes. Results indicated that 2-DG addition increased the activities of glucosyltransferase and inhibited UDP-glucose pyrophosphorylase activity. The result indicated that 2-DG inhibited glycolysis and changed metabolic driving force to activate gellan gum biosynthesis metabolism pathways.