CYANIDE METABOLISM IN BACTERIA AND PLANTS

Abstract

The metabolism of organic cyanides and amides was investigated in a species of Rhodococcus newly isolated from garden soil for its capacity to use acetonitrile as sole C and N source. Acetonitrilegrown cells hydrolysed a number of nitriles and amides to ammonia; although hydrogen cyanide CHCN1 may have also been hydrolysed thus, the results were close to experimental uncertainty. The bacterium was shown to utilise a variety of amides as the sole source of C and/or N for growth although it could not grow with every corresponding nitrile. Succinate/ammonium sulphate grown cells did not hydrolyse acetonitrile or acetamide indicating that the enzymes involved in nitrile degradation are subject to induction. Acetamide and acetate appeared to be gratuitous inducers of the acetonitrilase; acetate also induced the acetamidase. Optimum conditions were sought for assaying the acetonitrilase and acetamidase activities in whole bacteria. These enzyme activities were also detected in cell-free extracts although the cells proved difficult to disrupt. The nitrilase was found to be particularly thermolabile whether assayed using whole bacteria or extracts. Freezing this enzyme in the soluble form resulted in total loss of activity. The amidase was more thermostableand cell-free extracts retained the ability to hydrolyse acetamide after being frozen although the activity was greatly reduced. The metabolism of HCN was investigated further in a variety of higher plants including both cyanogenic and non-cyanogenic species. The enzymes investigated were 8-cyanoalanine synthase, rhodanese and formamide hydro-lyase. $-Cyanoalanine synthase was found to be present in every higher plant tested whereas rhodanese occurred far less commonly. Formamide hydro-lyase activity was not detected in any of the higher plants tested. Furthermore, a general trend was apparent between the HCN-potential of each plant and cyanide metabolising activity, in that the higher the HCN-potential, in general, the higher the cyanide metabolising activity.