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A mutant of thermotolerant Aureobasidium pullulans was isolated using growth inhibitors viz. nystatin and deoxyglucose in the growth medium. An improved mutant strain, RG-5, was developed using methyl methane sulfonate (MMS) (0.5%) for 5 minutes, having killing rate of 70% level, produced 6 g l-1 higher pullulan as compared to the wild type without loosing thermotolerant and non-melanin producing ability. The mutant required 15 rpm higher agitation as compared to the wild type and consumed 1% and 0.1% less sucrose and ammonium sulphate, respectively than the wild strain with lesser incubation period (12h), and with slight increase of pH optima (6.5) in a fed-batch fermentation process. This mutant is very stable and producing significantly higher pullulan with lesser carbon and nitrogen as well as pH tolerance capacity along with lesser incubation period. Therefore, the mutant can be used for industrial production in order to reduce the cost of production.
Key words: Aureobasidium pullulans, pullulan, mutant, methyl methane sulfonate (MMS).