Isolation and Characterization of Rhodanese from Bacillus licheniformis Obtained from Industrial Effluents of Steel Rolling Industry in Ilorin

Adeola Folashade Ehigie, Raphael Emuebi Okonji, Wasiu Ayinde Oladiran, Ona Leonard Ehigie

Abstract

Pollution from industrial effluents and anthropogenic sources is becoming a very big ecological problem in Nigeria. A typical example of such pollutants is cyanide which can be degraded to a less toxic compound by some microorganism. Some facultative anaerobic bacteria such as Bacillus licheniformis utilizes cyanide as a substrate for survival in industrial contaminated and polluted ecosystem.  This study screened for bacterial from industrial effluents in Ilorin that can synthesize rhodanese, an enzyme that can degrade cyanide to less toxic substance.

Bacillus licheniformis was isolated and biochemically characterized. Rhodanese was partially purified using 85% ammonium sulphate precipitation, ion exchange chromatography on Sephadex CM-50. The molecular weight of the enzyme was determined on a gel filtration column (Sephadex G-100) and finally on Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE). The kinetic parameters (Km and Vmax) were determined. Statistical analysis was performed using one-way analysis of variance and results were considered significant at p<0.05.

The result of this study showed that the optimum growth temperature for B. licheniformis was 35oC at a pH 9.0 while the highest duration time for the synthesis of rhodanese was 39 hours. Potassium cyanide (KCN) and casein were the best carbon and nitrogen sources. The B. licheniformis isolate synthesizes rhodanese that had a specific activity of 13.63 RU/mg, with a purification fold of 5.19, a percentage yield of 13.96% and an estimated native molecular weight of 34.44 kDa. The apparent   Km for KCN and Sodium thiosulphate (Na2S2O3) were determined to be 32.9 mM and 21.0 mM respectively while their Vmax were 5.6 RU /ml/min and 6.4 RU /ml/min respectively.  The optimum pH and temperature of partially purified enzyme were 8.0 and 50oC respectively. The enzyme showed high stability at 50oC for 30 minutes. The enzyme showed specificity at 6.78 RU/ml/min and equally showed specificity for Na2S2O3 while it was inhibited by other sulphur containing compounds such as 2-mercaptoethanol (2-MCPE), ammonium persulphate (NH4)2S2O8), and sodium metabisulphite (Na2S2O5). The enzyme activity was not inhibited by metal ions such as (K+, Mg2+, Ba2+, Ni2+, Sn2+ and Na+) at 1 mM and 10 mM and this was not significant (p>0.05).

The high level of expression of rhodanese in B. licheniformis suggests that the enzyme possess functional cyanide detoxification mechanism, a bioremediation process for the survival of both plants and animals in the environment. Microbial enhancement of this kind is recommended to help in reduction of toxic materials from industrial effluents.

Keywords

Bacillus licheniformis

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