Abstract

Objective of the Study: To enhance the production of biopolymer (Dextran) by suppressing the levansucrase from Leuconostoc mesenteroides KIBGE IB-22 using Ultraviolet (UV) rays. Methods: Isolated indigenous strain L. mesenteroides KIBGE IB-22 was irradiated with UV (240nm) at different time intervals. The strain was selected on the basis of higher enzyme production by means of enzyme activity and dextran production. SDS-PAGE was performed for molecular weight of dextransucrase and their expression pattern. Different fermentation parameters were optimized for the significant production of dextran from both strains (wild and mutant) of L. mesenteroides. 13C and 1H proton NMR spectra were performed for structural characterization and purity of biopolymer. Results: The mutant strain KIBGE IB-22M20 showed the double production of dextran in half time than wild type strain while the substrate consumption was also increased. After UV irradiation, SDS-PAGE revealed a single band that was specific for dextransucrase unlikely the wild strain that was expressing levansucrase as well. These results were further validated by 13CNMR analysis of the polymer produced by the mutant and results revealed that anomeric signals at 97.2 specific for alpha 1-6 configuration confirmed the presence of dextran only and deviating from wild type (KIBGE IB-22), which showed the two anomeric signals at 97.2 and 10.2 ppm corresponding to the presence of dextran and levan. In addition, 1H proton NMR analysis revealed that signal region between 3.4 and 4.2 ppm of IB-22 was much packed and expressed more characteristic peaks that were dextran and levan. Product of IB-22M20 showed only the characteristics peaks of dextran. After all these results, it was confirmed that the isolated strain produces two types of biopolymer: dextran and levan. And after UV irradiation, production of levan was suppressed. Conclusion: High yield of dextran was achieved by KIBGE IB-22M20, which has suppression of levansucrase resulting in the increased availability of substrate for the dextransucrase.