Enzymatic decolourization of Congo red and methyl red by Malaysian Rhodococcus

The textile industry consumes a lot of water, of which about 90 % is released in the form of wastewater. Textile wastewater contains dyes as the main pollutant. Dyes are not only toxic but also affect the aesthetic value of wastewater due to the presence of strong colours. Inadequate treatment of textile wastewater leads to serious environmental problems and negatively impacts aquatic organisms. Therefore, in the current research work, the ability of Malaysian Rhodococcus strains to decolourize azo dyes was evaluated through the activity of azo dye-decolourizing enzymes. The cell-free extract of Rhodococcus strain UCC 0016 exhibited an elevated titre of intracellular azoreductase by 317 % and intracellular laccase by 273 % compared to the extracellular counterpart, respectively. It was interesting to discover the presence of azoreductase and laccase constitutively and the production of these enzymes escalated when induced with Methyl red. When these enzymes were subjected to the decolourization of 0.5 g/L Methyl red, 99 % Methyl red-decolourizing activity was detected in the absence of mediators after 2 hours of incubation period, making this method attractive in terms of cost. Furthermore, the crude enzyme from Rhodococcus strain UCC 0010 optimized at acidic condition was analysed using SDS-PAGE which revealed the visualization of a protein band at approximately 40 kDa, which is consistent with the properties of laccase. Collectively, these discoveries provided the fundamental information to further advance the features of the crude enzymes namely using the immobilization technology for sustainable application in the bioremediation of textile wastewater.