Introduction

The aim of this chapter is to review the biodegradation of cyanide and its metal complexes by fungi. However, since the degradation of cyanides by bacteria is in many ways similar to that of fungi, bacterial cyanide metabolism will also be considered. There are also many examples of the degradation and utilization of organic cyanides (nitriles) by both bacteria and fungi, although these are outside the scope of this article and will not be examined. For completion, the ability of fungi to produce cyanide (cyanogenesis) will be briefly discussed, as cyanogenic species have the ability to biotransform or biodegrade cyanide. Reviews that cover more specific aspects of microbial cyanide metabolism include Knowles (1976, 1988), Knowles & Bunch (1986), Raybuck (1992), and Dubey & Holmes (1995).

Cyanide chemistry and toxicity

The identification of cyanide as a poison in bitter almonds and cherry laurel leaves dates back to the early Egyptians (Sykes, 1981). Indeed, hydrogen cyanide (HCN) may account for more human deaths throughout history than any other toxin because of its use in executions and large-scale genocide during World War II (Way, 1981).

Hydrogen cyanide is one of the most rapidly acting metabolic inhibitors known, because of its universal inhibition of respiration. By binding to Fe3+ in cytochrome c oxidase, the terminal oxidase of the mitochondrial or bacterial respiratory chain, cyanide inhibits electron transfer to oxygen, and therefore respiration (Stryer, 1988).