Cyanide utilization in Pseudomonas fluorescens NCIMB 11764 involves a putative siderophore

Cyanide utilization in P. fluorescens NCIMB 11764 requires the induction of cyanide oxygenase. The enzyme is induced during growth on cyanide as the sole nitrogen source or when cyanide is added to stationary-phase cells grown on limiting ammonia, however, enzyme induction and cyanide degradation were found to occur non-concomitantly. Cyanide removal by chloramphenicol-treated cells and a mutant strain (JL102) defective in cyanide oxygenase were also observed. We now report a non-enzymatic mechanism for cyanide biotransformation by an iron-chelating species identified as a putative siderophore. Partially purified siderophore preparations removed cyanide at initial rates as high as 7.6 mmol min⁻¹ mg⁻¹. The reaction product was further shown to be enzymatically oxidized to NH₃ (and CO₂) and also supported growth. The results indicate that both cyanide oxygenase and a putative siderophore component are involved in cyanide utilization.