Journal of Pure and Applied MicrobiologyVol. 9 No. 2

Immobilised Rhodococcal Cells: A Competent Approach for Phenol Degradation by Rhodococcus sp. NAM 81

Norazah Mohammad Nawawi1,2, Siti Aqlima Ahmad1*, Mohd Yunus Shukor1, Mohd Arif Syed1 and Abdul Latif Ibrahim2

1Department of Biochemistry, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, UPM 43400 Serdang, Selangor, Malaysia. 2Institute of Bio-IT Selangor, Universiti Selangor, Jalan Zirkon A7/A, Seksyen 7, 40000 Shah Alam, Selangor, Malaysia.

Received on 24 February 2015 and accepted on 15 April 2015

 

ABSTRACT

The objective of this current work is to study about phenol degradation ability of the immobilised Rhodococcus sp. NAM81. The present investigation evaluates the suitability of five matrices; gellan gum, calcium alginate, agarose, agar-agar and polyacrylamide upon the immobilisation of Rhodococcus sp. NAM81 for phenol degradation. Among all of these matrices, gellan gum was proven to be the most effective and suitable matrix as it exhibits higher phenol degradation (99.9%) compared to other matrices studied. Maximum phenol degradation has been achieved at gellan gum with the concentration of 0.7% (w/v), bead size of 4 mm diameter (estimated surface area of 50.26 mm2), 4 g/Lof cell loading and 350 numbers of beads per 100 mL medium. Both free and immobilised bacteria exhibited similar rates of phenol degradation at phenol concentration of 100 mg/L, the immobilised bacteria exhibited a higher degradation rate of phenol at higher phenol concentrations. The immobilised cells completely degraded phenol within 108, 216, and 240 h at 1100, 1500 and 1900 mg/L phenol, respectively, whereas free cells took 240 h to completely degrade phenol at 1100 mg/L.However, the free cells were incapable of completing phenol degradation at higher concentrations. Overall, the rates of phenol degradation by both immobilised and free bacteria decreased gradually as phenol concentration increased. It also proved that inhibition by heavy metals and respiratory inhibitors decreased by gellan gum encapsulated the cells. The immobilised cells showed no sign of losses in phenol degrading activity after being used repeatedly for 50 times of 18 h cycle and still stable after storing at 4?C for 28 days. The study has showed that the effectiveness of phenol degradation was greater using immobilised cells in gellan gum compared to free living cells. Presumably, this is the first attempt of phenol degradation using the immobilised Rhodococcus sp in gellan gum. The gellan gum-immobilised cells showed potential candidature for phenol degradation.

Keywords : Rhodococcus sp.,encapsulation, gellan gum, phenol, biodegradation.