Production and optimization of curdlan produced by Pseudomonas sp. QL212

Curdlan is a polysaccharide that consists of β-1,3-linked glucose residues. A polysaccharide-producing bacterium isolated from soil samples was identified as Pseudomonas sp. QL212. The polysaccharide was purified to homogeneity via sequential ethanol precipitation, deproteinization, CM ion-exchange, and gel chromatography sequentially. Analysis of the purified polysaccharide revealed that it consisted of many glucosyl residues, and its molecular weight was only 6.18 × 105 Da. This low molecular weight endowed it with excellent solubility. Infrared and nuclear magnetic resonance spectral analysis confirmed that the polysaccharide was curdlan. Single-factor and Response surface methodology experiments were used to optimize the culture medium and conditions. The optimal culture conditions consisted of seed culture age of 12 h, and an incubation temperature of 30 °C, with 10% inoculum and a total fluid volume of 75 mL in a 250-mL Erlenmeyer flask. The maximum curdlan yield of about 5.92 g L−1 was achieved with an optimal medium consisting of 30.11 g L−1 of sucrose, 5.94 g L−1 of yeast extract, and an initial pH of 8.03. To our best knowledge, this is the highest reported yield of curdlan produced by Pseudomonas sp., and the curdlan production medium components were much simpler than those in previous reports.