Isolation and Assessment of Cyanide Biodegradation Potential of Indigenous Bacteria from Contaminated Soil

Eight effective bacterial strains were isolated from cyanide-contaminated soil, from which, two (S11 and S13) were tested to determine their minimum inhibitory concentration using potassium cyanide (KCN) and potassium tetracyano nickelate (K2Ni(CN) 4). The isolates were tested for their KCN biodegradation potential (by measuring ammonia production) at neutral and alkaline pHs (7.0 and 9.0). Furthermore, the effect of the initial KCN concentration on biodegradation was evaluated at the optimal pH using nitrogen free M9 medium, supplemented with KCN as nitrogen source. The results showed that both strains tolerated cyanide concentrations of up to 10 × 10-3 mol⋅l-1 (0.651 g⋅l-1 KCN;2.409 g⋅l-1 K2Ni(CN)4) which makes them good candidates for cyanide bioremediation. For both strains, a change of initial pH from 7.0 to 9.0 significantly enhanced KCN degradation. S13 grown at pH 9.0 and S11 cultivated at pH 7.0 released the highest and lowest amounts of ammonia, respectively. For both strains, the release of ammonia increased when the initial KCN concentration increased from 10-3 to 5 × 10-3 mol⋅l-1. These findings open prospects for the application of these bacteria for remediation of cyanide-contaminated soils and wastewater at alkaline pH, alkaline pH being conditions that prevent cyanide volatilization.