ABSTRACT
Commercial bacterial exopolysaccharide (EPS) applications have been gaining interest; therefore, strains that provide higher yields are required for industrial-scale processes. Succinoglycan (SG) is a type of bacterial anionic exopolysaccharide produced by Rhizobium, Agrobacterium, and other soil bacterial species. SG has been widely used as a pharmaceutical, cosmetic, and food additive based on its properties as a thickener, texture enhancer, emulsifier, stabilizer, and gelling agent. An SG-overproducing mutant strain (SMC1) was developed from Sinorhizobium meliloti 1021 through N-methyl-N'-nitro-N-nitrosoguanidine (NTG) mutation, and the physicochemical and rheological properties of SMC1-SG were analyzed. SMC1 produced (22.3 g/L) 3.65-fold more SG than did the wild type. Succinoglycan (SMC1-SG) overproduced by SMC1 was structurally characterized by FT-IR and 1H NMR spectroscopy. The molecular weights of SG and SMC1-SG were 4.20 × 105 and 4.80 × 105 Da, respectively, as determined by GPC. Based on DSC and TGA, SMC1-SG exhibited a higher endothermic peak (90.9 °C) than that of SG (77.2 °C). Storage modulus (G') and loss modulus (Gâ³) measurements during heating and cooling showed that SMC1-SG had improved thermal behavior compared to that of SG, with intersections at 74.9 °C and 72.0 °C, respectively. The SMC1-SG's viscosity reduction pattern was maintained even at high temperatures (65 °C). Gelation by metal cations was observed in Fe3+ and Cr3+ solutions for both SG and SMC1-SG. Antibacterial activities of SG and SMC1-SG against Escherichia coli and Staphylococcus aureus were also observed. Therefore, like SG, SMC1-SG may be a potential biomaterial for pharmaceutical, cosmetic, and food industries.
ABSTRACT
We fabricated new hydrogels using polyvinyl alcohol (PVA) and succinoglycan (SG) directly isolated and obtained from Sinorhizobium meliloti Rm 1021 via the freeze-thaw method. Both the composition of the hydrogels and the freeze-thaw cycles were optimized to maximize the swelling ratio for the preparation of the PVA/SG hydrogels. During the optimization process, the morphology and conformational change in the hydrogel were analyzed by scanning electron microscopy, rheological measurements, and compressive tests. An optimized hydrogel with a maximum swelling ratio of 17.28 g/g was obtained when the composition of PVA to SG was 50:50 (PVA/SG 50/50) and the total number of freeze-thaw cycles was five. The PVA/SG 50/50 hydrogel had the largest pore with 51.24% porosity and the highest cross-over point (28.17%) between the storage modulus (G') and the loss modulus (Gâ³). The PVA/SG 50/50 hydrogel showed improved thermal stability owing to its interaction with thermally stable SG chains. The improvement in the thermal stability was confirmed by thermogravimetric analysis and differential scanning calorimetry. In addition, the PVA/SG 50/50 hydrogel showed differential drug release according to the corresponding pH under acidic conditions of pH 1.2 and slightly basic conditions of pH 7.4. Furthermore, the cell viability test on the HEK-293 cell line for that hydrogel demonstrated that the PVA/SG 50/50 hydrogel was non-toxic and biocompatible. Therefore, this hydrogel could be a potential scaffold capable of pH-responsive drug delivery for chronic wound dressing applications.
ABSTRACT
Since succinoglycan (SG) produced by Sinorhizobium meliloti is an anionic polysaccharide having substituents such as succinate and pyruvate groups, a polyelectrolyte composite hydrogel can be made together with chitosan (CS), a cationic polysaccharide. We fabricated polyelectrolyte SG/CS hydrogels using the semi-dissolving acidified sol-gel transfer (SD-A-SGT) method. The hydrogel showed optimized mechanical strength and thermal stability at an SG:CS weight ratio of 3:1. This optimized SG/CS hydrogel exhibited a high compressive stress of 497.67 kPa at 84.65 % strain and a high tensile strength of 9.14 kPa when stretched to 43.73 %. Additionally, this SG/CS hydrogel showed a pH-controlled drug release pattern for 5-fluorouracil (5-FU), where a change from pH 7.4 to 2.0 increased the release from 60 % to 94 %. In addition, this SG/CS hydrogel not only showed a cell viability of 97.57 %, but also showed synergistic antibacterial activity of 97.75 % and 96.76 % against S. aureus and E. coli, respectively. These results indicate the potential of this hydrogel as a biocompatible and biodegradable hydrogel material for wound healing, tissue engineering, and drug release systems.
