Decolourization and biodegradation of azo dye methyl red by Rhodococcus strain UCC 0016

ABSTRACT

In the present study, locally isolated Rhodococcus strains were attempted as biological tools for methyl red removal, a mutagenic azo dye posing threat to the environment if left untreated. Rhodococcus strain UCC 0016 demonstrated superior methyl red-decolourizing activity of 100% after 24 h at static condition in comparison to Rhodococcus strain UCC 0008 which recorded 65% decolourization after 72 h. Optimization of physicochemical parameters at 30°C, pH 7 and supplementing glucose as the carbon source resulted in improved methyl red-decolourizing activity at static condition and reduced the time taken to achieve complete decolourization by 80%. Higher concentration of methyl red (5 g/L) was able to be decolourized completely within 10 h by adopting the technology of immobilization. The encapsulated cells of Rhodococcus strain UCC 0016 demonstrated higher substrate affinity (K_m = 0.6995 g/L) and an accelerated rate of disappearance of methyl red (V_max = 0.3203 g/L/h) compared to the free cells. Furthermore, the gellan gum beads could be reused up to nine batches without substantial loss in the catalytic activity indicating the economic importance of this protocol. Analysis of methyl red degradation products revealed no germination inhibition on Triticum aestivum and Vigna radiata demonstrating complete toxicity removal of the parent dye after biological treatment. The occurrence of new and altered peaks (UV–Vis and FTIR) further supported the notion that the removal of methyl red by Rhodococcus strain UCC 0016 was indeed through biodegradation. Therefore, this strain has a huge potential as a candidate for efficient bioremediation of wastewater containing methyl red.

GRAPHICAL ABSTRACT

KEYWORDS:

• Biodegradation
• decolourization
• immobilization
• methyl red
• Rhodococcus strain UCC 0016

Acknowledgements

Maegala Nallapan Maniyam designed the project, carried out the experimental research, performed data analysis and wrote the manuscript. Abdul Latif Ibrahim and Anthony E. G. Cass mentored and gave undivided guidance in data analysis and discussion of the research findings. This paper is dedicated to the memory of the late Dr Judit Nagy, who was an inspirational woman and more importantly an outstanding scientist.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors would like to acknowledge the Ministry of Science, Technology and Innovation (MOSTI) (Kementerian Sains, Teknologi dan Inovasi), Malaysia [3090104000 (G)] for the financial assistance.