Cloning and expression of gellan gum biosynthetic genes gelQ, gelB, gelL and gel K of Sphingomonas paucimobilis, production and characterization of the recombinant gellan gum

Abstract

Abstract Gellan gum, a linear exopolysaccharide produced by Sphingomonas paucimobilis, is one of the most multifunctional polymers used in food, cosmetics and pharmaceutical industries. In the present study, for the first time, the gellan gum biosynthetic genes gel Q, gel B, gel L and gel K of Sphingomonas paucimobilis were cloned and successfully expressed in the same bacterium using the vector, pBBR122. The recombinant proteins were purified using Ni-NTA column chromatography and the molecular weight was predicted using SDS-PAGE. The biomass and gellan gum production of the strains harboring the expressed genes were analyzed in a laboratory fermentor and the production was higher with recombinant gel Q gene (Biomass: 7.03 ± 0.1 g/l; Gellan gum: 11.71 ± 0.2 g/l) compared to recombinant strains expressed with gel B, gel K and gel L genes. The optimum gellan gum production was obtained at 30 °C, pH 6.5, 400 rpm agitation speed, 90% Dissolved oxygen level and carbon-nitrogen ratio 3. The viscosity of polymer decreased with an increased shear rate which substantiates the use of this exopolysaccharide as a better gelling and thickening agent. The glucose: glucuronic acid: rhamnose ratio of the recombinant polymer was around 2:1:1 which is similar to the structural property of its native gellan. Different shapes like disc, membrane, fibres, particles and beads of gellan were made which may have wide applications in tissue engineering and drug delivery. The water holding capacity of the gellan gum gel was maximum in 100 mM calcium and minimum in gel with 5 mM Ca2+at 60 min. Compression test results illustrated that there was no significant change in the textural property of the recombinant gellan for different storage intervals compared to native gellan.