Characterization of rhodanese produced by Pseudomonas aeruginosa and Bacillus brevis isolated from soil of cassava processing site

Abstract

Wastewater from numerous cassava processing industries contains cyanide which is toxic to several forms of life. This effluent constitutes serious hazards to the environment and aquatic life in receiving water bodies. Enzymatic remediation of polluted environment presents advantages over traditional technologies and also over microbial remediation. Extracellular rhodanese of strains of Pseudomonas aerugionosa and Bacillus brevis isolated from soil of cassava processing site were studied. Biochemical characteristics of the purified enzymes, including pH and temperature profiles were also determined. Production of rhodanese correlated with the rate of bacterial growth at the exponential phase for both strains. Optimum incubation time for maximum enzyme production was 20 h in both cases. The enzyme was purified 9.72-fold with a yield of 37.8% and specific activity of 6.32 mg^-1 protein in the case of P. aeruginosa. The enzyme from B. brevis was purified 7.44-fold with a yield of 22.6% and specific activity of 5.21 mg^-1 protein. The enzyme generally demonstrated a broad pH range but optimum pH was 6.0 and 7.0 for P. aeruginosa and B. brevis rhodanese activity respectively. Optimum temperatures for P. aeruginosa and B. brevis rhodanese were 50 and 40°C, respectively, with both enzymes retaining activity up to 70°C. The Km values for KCN and Na₂S₂O₃ as substrates for P. aeruginosa rhodanese were 12.5 and 0.0066 mM, respectively, while the Km values for the same substrates for B. brevis rhodanese were 3.12 and 11.1 mM, respectively. Cations, Hg²⁺, Ba²⁺, and Co²⁺ all inhibited the enzyme activities of both bacteria. The bacteria rhodaneses have potential for effective remediation of cyanide-polluted environments, ultimately leading to improvement of fish and other aquatic organisms in receiving water bodies.

Keywords: Cyanide, cyanogenic glycosides, cassava mill wastewater, rhodanese, Pseudomonas aeruginosa, Bacillus brevis

African Journal of Biotechnology Vol. 12(10), pp. 1104-1114