Biodegradation of cyanide by Rhodococcus UKMP-5M

Abstract

A new bacterial strain, Rhodococcus UKMP-5M isolated from petroleum-contaminated soils demonstrated promising potential to biodegrade cyanide to non-toxic end-products. Ammonia and formate were found as final products during growth of the isolate with KCN as the sole nitrogen source. Formamide was not detected as one of the end-products suggesting that the biodegradation of cyanide by Rhodococcus UKMP-5M may have proceeded via a hydrolytic pathway involving the bacterial enzyme cyanidase. No growth of the bacterium was observed when KCN was supplied as the sole source of carbon and nitrogen even though marginal reduction in the concentration of cyanide was recorded, indicating the toxic effect of cyanide even in cyanide-degrading microorganisms. The cyanide biodegradation ability of Rhodococcus UKMP-5M was greatly affected by the presence of organic nutrients in the medium. Medium containing glucose and yeast extract promoted the highest growth rate of the bacterium which simultaneously assisted complete biodegradation of 0.1 mM KCN within 24 hours of incubation. It was found that growth and cyanide biodegradation occurred optimally at 30• C and pH 6.3 with glucose as the preferred carbon source. Acetonitrile was used as an inducer to enhance cyanide biodegradation since the enzymes nitrile hydratase and/or nitrilase have similarity at both the amino acid and structural levels to that of cyanidase. The findings from this study should be of great interest from an environmental and health point of views since the optimum conditions discovered in the present study bear a close resemblance to the actual scenario of cyanide wastewater treatment facilities.

Biodegradation of Cyanide under Alkaline Conditions by a Strain of Pseudomonas Putida Isolated from Gold Mine Soil and Optimization of Process Variables through Response Surface Methodology (RSM)

“…Cyanide removal efficiency in the first case was four times more than in the second one. This indicated significantly higher effect of glucose than yeast extract, as cyanide degradation occurred partially by using yeast extract [1]. In addition, Dumestre et al [25] examined the degradation of cyanide under alkaline conditions by a strain of Fusarium solani isolated from contaminated soils in both the presence and absence of yeast extract.…”

“…However, considering the negligible enhancement (~1.5%), feasibility studies and economic analysis should be conducted prior to the industrial application of yeast extract. Maniyam et al [1] studied the biodegradation of cyanide by Rhodococcus. They analyzed the effect of glucose and yeast extract on bacterial growth and cyanide removal efficiency at two cases.…”

“…A number of these organisms use cyanide solely as their nitrogen source [1,8,9], while for some others, the previous compound provides both carbon and nitrogen sources [10][11][12]. Biodegradation of cyanide compounds may occur in the presence of various carbon sources including simple carbohydrates, e.g.…”

“…[20], Pseudomonas pseudoalcaligenes [15], and Agrobecterium tumefaciens [21], are the related examples. A recent bacterial species "Rhodococcus UKMP-5M" capable of degrading cyanide to less toxic compounds has been isolated from petroleum-contaminated soils [1]. In another study, two fungi mixtures in which one comprising Fusarium solani and Trichoderma polysporum, and the other consisting of Fusarium oxysporum, Scytalidium thermophilum, and Penicillium miczynski, as well as both being capable of consuming iron-or nickel-cyanide complex, as their nitrogen source, under acidic or neutral conditions were isolated from acidic soils of gas-production factories [22].…”

“…Cyanide is produced by a number of fruits, seeds, leaves, and roots of various plants such as cassava, a number of soil bacteria, fungi, and various species of invertebrates [1,2]. Nevertheless, industrial wastes of human activities contribute the largest portion of environmental cyanide pollution [3,4].…”