Detoxification of cyanide by immobilised fungi

Abstract

Cyanide detoxification was studied by immobilisation of fungal mycelia that had been induced to form cyanide hydratase (formamide hydrolyase) which is able to hydrolyse cyanide to formamide. The fungal pathogens of cyanogenic plants, Stemphylium loti, Gloeocercospora sorghi and Fusarium moniliforme were immobilised using polyelectrolyte flocculating agents. The effect of immobilisation on the enzymic properties of S. loti and G. sorghi were investigated. The apparent Km values increased from 21.0 mmol and 25.5 mmol KCN to 43.5 mmol and 71.0 mmol KCN, respectively. The pH profile for the two enzymes widened on immobilisation. The stoichiometry of 1:1 cyanide utilisation to formamide formation was retained on immobilisation, with complete conversion of 70 mmol KCN in 120 min by 0.12 g dry wt of S. loti and in 6 min by 0.13 g dry wt of G. sorghi. When the two fungi were stabilised by immobilisation, and tested in column reactors containing 1.2 g dry wt of S. loti and 1.3 g dry wt of G. sorghi, they completely converted cyanide (70 mmol; added continuously at 7.5 ml h−1) into formamide for 2 days and 30 days, respectively. Stability was enhanced by inclusion of 1.0 mmol glucose in the 70 mmol KCN solution, by a further 10 h for S. loti and an extra 10 days for G. sorghi. Operational stabilities of immobilised G. sorghi (1.3 g dry wt) and F. moniliforme (1.0 g wet wt) in column reactors, with 100 % cyanide conversion, at varying flow rates was investigated. G. sorghi was stable for 15, 10 and 2 days whereas F. moniliforme was only stable for 48, 20 and 10 h at 30, 60 and 120 ml h−1 flow rates respectively.

Enzymatic mechanism and biochemistry for cyanide degradation: A review

“…It was observed that Gloeocercospora sorghi fungus when immobilized after induction of cyanide hydratase with exposure to 0.5 mM KCN at 10-12 h before harvesting [45]. K m for cyanide doubled to 40-70 mM and also enzyme stability was dramatically increased to 30 days.…”

Study on Optimization of Fermentation Condition for Nitrilase-Producer <i>Escherichia Coli BL21 (DE3)/pET-Nit</i>

“…Nitrile, a class of strong toxic compounds, is important chemical raw material. However, nitriles are pollutants of soils and industrial waste waters with a wide distribution in the environment [1]. Nitriles occur naturally in plants and in microbial metabolism as intermediates [2][3][4].…”