Strain improvement in dye decolourising mutants of Mucor mucedo by protoplast fusion

Abstract

The amounts of protoplasts obtained in the developed mutants of M. mucedo MMM1 (U.V. irradiated mutant) and MMM2 (ethyl methyl sulfonate treated mutant) which are very effective decolourisers were 5.23 x 106 and 5.65 x 106 protoplasts/ml respectively. Among the 385 colonies isolated after protoplast fusion only 3 possessed clamp connections and chosen as fusants (MMFu1, MMFu2 and MMFu3). Of the 3 fusants, MMFu3 showed maximum growth rate on potato dextrose agar plates incubated at room
temperature. The fusant MMFu3 showed very good increase in the production of three enzymes protease (1.90 U/ml), peroxidase (1100 U/ml) and laccase (200 U/ml) when compared to the two parent
strains proving that the higher enzymatic secretions are responsible for the decolourisation activity. In protease isozyme analysis, fusants showed bands common to either of the parental strains or to both. Further non parental new bands were observed in the protease isozyme patterns of MMFu3. This fact indicated that the isolates were fusants between MMM1 and MMM2. The fusant MMFu3 showed the maximum decolourisation of crystal violet up to 95% and malachite green up to 84% after 10 days of
incubation. The results clearly indicated that the protoplast fusants showed improvement in the decolourisation efficiency in both the cases of crystal violet and malachite green.