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Gellan gum is a microbial exopolysaccharide, produced after aerobic fermentation using the Gram-negative bacterium strain Sphingomonas elodea ATCC 31461. Due to its unique structure and excellent physical characteristics, gellan gum has a broad range of applications in food, pharmaceutical, and other industries where it is used for stabilizing, emulsifying, thickening, and suspending. During the fermentative production of gellan, strain ATCC 31461 also accumulates large amounts of the metabolic by-products yellow carotenoid pigments and poly-β-hydroxybutyrate (PHB), which is decreasing the gellan production and increasing processing costs. A pigment PHB-free mutant was obtained by knocking out the phytoene desaturase gene ( crtI ) in the carotenoid biosynthetic pathway and the phaC gene, encoding a PHB synthase for the polymerization of PHB. Unfortunately, the double gene knockout mutant produced only 0.56 g liter -1 gellan. Furthermore, blocking PHB and carotenoid synthesis resulted in the accumulation of pyruvate, which reduced gellan production. To elevate gellan production, combined UV irradiation and ethyl methanesulfonate (EMS) mutagenesis treatment were used. A mutant strain with the same level of pyruvate as that of the wild-type strain and higher gellan production was isolated (1.35 g liter -1 , 132.8% higher than the double gene knockout mutant and 14.4% higher than the wild-type strain ATCC 31461). In addition, a new gellan gum recovery method based on the new mutant strain was investigated, in which only 30% isopropanol was required, which is twice for the wild-type strains, and the performance of the final product was improved. Thus, the mutant strain could be an ideal strain for the commercial production of gellan. IMPORTANCE A carotenoid- and PHB-free double gene knockout strain mutant was constructed to simplify the purification steps normally involved in gellan production. However, the production of gellan gum was unexpectedly reduced. A mutant with 14.4% higher gellan production than that of the wild-type strain was obtained and isolated after employing UV and EMS combined mutagenesis. Based on this high-yield and low-impurity-producing mutant, a new recovery method requiring less organic solvent and fewer operating steps was developed. This method will effectively reduce the production costs and improve the economic benefits of large-scale gellan production., (Copyright © 2019 Li et al.)

In a water-organic solvent, two-phase conversion system, CoQ(10) could be produced directly from solanesol and para-hydroxybenzoic acid (PHB) by free cells of Sphingomonas sp. ZUTE03 and CoQ(10) concentration in the organic solvent phase was significantly higher than that in the cell. CoQ(10) yield reached a maximal value of 60.8 mg l(-1) in the organic phase and 40.6 mg g(-1)-DCW after 8 h. CoQ(10) also could be produced by gel-entrapped cells in the two-phase conversion system. Soybean oil and hexane were found to be key substances for CoQ(10) production by gel-entrapped cells of Sphingomonas sp. ZUTE03. Soybean oil might improve the release of CoQ10 from the gel-entrapped cells while hexane was the suitable solvent to extract CoQ(10) from the mixed phase of aqueous and organic. The gel-entrapped cells could be re-used to produce CoQ(10) by a repeated-batch culture. After 15 repeats, the yield of CoQ(10) kept at a high level of more than 40 mg l(-1). After 8 h conversion under optimized precursor's concentration, CoQ(10) yield of gel-trapped cells reached 52.2 mg l(-1) with a molar conversion rate of 91% and 89.6% (on PHB and solanesol, respectively). This is the first report on enhanced production of CoQ(10) in a two-phase conversion system by gel-entrapped cells of Sphingomonas sp. ZUTE03.

The use of coenzyme Q(10) (CoQ(10)) as a complementary therapy in heart failure will increase in proportion to the growth of the ageing population and the expansion of statins consumption. Economical production of CoQ(10) by microbes will become more important due to the growing demands of the pharmaceutical industry. Process simplification and integration might be one desirable pathway for economic production of CoQ(10) by microbial fermentation. In this report, the effect of a coupled fermentation-extraction process on CoQ(10) production by newly isolated Sphingomonas sp. ZUTEO3 was evaluated. It was found that the CoQ(10) yield of the coupled process was significantly higher than that of the traditional process. As optimal conditions in our experiment, 2% soybean oil was added to the original culture to enhance cell membrane permeability, and 50 mL hexane was added to the 30 h culture as an extracting solvent for the subsequent coupled fermentation-extraction process. The maximal yield of CoQ(10) reached 43.2 mg/L and 32.5 mg/g dry cell weight after 38 h of total fermentation period. The coupled process represents one potential pathway for CoQ(10) production with even higher yield and lower cost. This is the first report of CoQ(10) production by Sphingomonas sp. using a coupled fermentation-extraction process.

Bacterial exopolysaccharides (EPS) are products of biotechnology that are of high interest due to their rheological properties. This is the case of sphingans, a group of structurally related EPS secreted by members of the genus Sphingomonas. Among these, gellan is a multifunctional gelling agent produced in high yields by the non-pathogenic strain Sphingomonas elodea ATCC 31461. In its native form, gellan is a linear anionic EPS based on a tetrasaccharide repeat unit composed of two molecules of D: -glucose, one of L: -rhamnose and one of D: -glucuronic acid. The native gellan is partially esterified with acyl substituents (1 mol of glycerate and 0.5 mol of acetate) per repeat unit. Gellan has unique characteristics and has many applications, particularly in the food, pharmaceutical, and biomedical fields. This review summarizes current knowledge on the structure and properties of gellan and provides details about the biosynthesis of this exopolysaccharide. In addition, a highlight of the importance of gellan in industrial and medicinal applications is given.