Immobilized cells of Rhodococcus strain UCC 0004 as source of green biocatalyst for decolourization and biodegradation of methyl orange

Abstract

Abstract The bulk presence of methyl orange is contributed by anthropogenic sources which poses substantial threat to health and the environment. Locally isolated Rhodococcus strains were used as alternatives to develop greener and cost effective methyl orange removal technology. Rhodococcus strain UCC 0004 in particular demonstrated complete removal of 0.5 g/L methyl orange after 2 days of incubation and this strain exhibited 513% higher methyl orange removal efficiency under static mode in comparison to agitated mode. Adopting the technology of immobilization enabled the decolourization of higher concentration of methyl orange which resulted in 66% greater methyl orange removal activity as opposed to the non-immobilized cells. Optimization of immobilization parameters at 0.4% (w/v) alginate concentration, 0.3 M CaCl2, 3 mm bead diameter and 50 beads led to improved methyl orange-decolourizing activity and reduced the time taken to achieve complete decolourization by 67%. The immobilized beads could be reused up to nine batches without significant loss of methyl orange-decolourizing ability which is advantageous economically. The immobilized cells demonstrated higher substrate affinity (Km = 0.3771 g/L) and accelerated rate of disappearance of methyl orange (Vmax = 0.05903 g/L/h) compared to free cells. No germination inhibition was observed on Triticum aestivum and Vigna radiata indicating complete removal of dye toxicity. The decolourization of methyl orange occurred through biodegradation as supported by complete disappearance of the major peak from UV–vis spectrum. Therefore, this strain has a huge potential to be developed as biological tool for efficient removal of wastewater containing methyl orange.