Effects of exopolysaccharide derived from Pantoea alhagi NX-11 on drought resistance of rice and its efficient fermentation preparation.

Exopolysaccharide (EPS) plays an important role in plant growth-promoting bacteria (PGPB)-mediated enhancement of plant abiotic stress resistance. In this study, it is found that EPS from Pantoea alhagi NX-11 foliar sprayed at 20, 50, and 100 ppm could significantly enhance drought resistance of rice seedlings. The fresh weight and relative water content of EPS sprayed were increased. In addition, malondialdehyde content reduced while total chlorophyll, proline and soluble sugar content, prominent enhanced. Meanwhile, the antioxidant enzymes, CAT, POD and SOD, were also significantly increased. The drought resistance of rice was most pronounced at the 50 ppm EPS dose. For the sake of commercializing the gram-negative EPS-producing PGPB which were difficult to preserve, it is vital to improve the EPS yield. First, the carbon source, nitrogen source and inorganic salt were optimized. Subsequently, the effect of three oxygen vectors, which could increase the efficiency of oxygen mass transfer, on EPS yield was studied by response surface methodology. The maximum EPS yield (19.27 g/L) was obtained, which is 51.7% higher than the initial yield of 12.7 g/L. Overall, it may provide a new way for the industrialization of PGPB to increase the yield of EPS.