2004, pp 671-687

Cyanogenesis

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Abstract

The production of hydrogen cyanide (HCN) by Pseudomonas aeruginosa and other fluorescent pseudomonads was discovered by Clawson and Young in 1913 when these authors identified, for the first time, cyanogenic bacteria isolated from different habitats18. Although the physiological conditions favoring HCN formation were not investigated in detail, the presence of oxygen was recognized as being important18. A further critical observation was made by Friedheim in 1934: he noted that the aerobic bacterium P. aeruginosa “lives almost as an anaerobic organism even in the presence of air.”27 As it turned out later, HCN is produced optimally by P. aeruginosa under microaerobic conditions10, 13, 14, to which this bacterium is well adapted61. In 1948, Lorck found glycine to be the metabolic precursor of HCN in P. aeruginosa 45. Biochemical details of the glycine-to-HCN conversion, worked out mostly by the groups of Wissing and Castric in the 1970s12, 82, were obtained in whole cells and cell extracts of two different pseudomonads. Due to technical difficulties, the proteins catalyzing HCN biosynthesis in pseudomonads have never been purified to homogeneity. Thus, the enzymatic mechanism and the structural model of HCN synthase, which are deduced, in part, from a genetic analysis of the hcn structural genes in Pseudomonas fluorescens CHA0 and P. aeruginosa PAO (discussed below), should be considered as working hypotheses. HCN formation from glycine appears to be restricted to strains of Pseudomonas spp. and Chromobacterium violaceurn 12,38. Other pathways producing cyanide occur in Escherichia coli and in some cyanobacteria, fungi, algae and plants35, 38, 59, 71.