ALTERNATIVE RESPIRATORY SYSTEM AND FORMAMIDE HYDRO-LYASE ACTIVITY AS THE KEY COMPONENTS OF THE CYANIDE-RESISTANCE MECHANISM IN FUSARIUM-OXYSPORUM

A strain of Fusarium oxysporum, isolated from an industrial effluent c ontaining a high cyanide concentration, detoxifies cyanide via formami de hydro-lyase (FHL). The importance of the coexistence of the alterna tive (cyanide insensitive) respiratory system and the synthesis of FHL was assessed. This enzyme, induced by cyanide, converts this compound to formamide and is partially responsible for the tolerance of F. oxy sporum to high cyanide concentration. The FHL induction for cyanide de toxification depends on the alternative respiratory system when the te rminal oxidase of the electron transport chain is blocked by cyanide u sed during the induction process. The respiratory metabolism of a F. o xysporum strain was studied. Whole cells exhibited a cyanide-sensitive respiration but developed a partially cyanide-resistant respiration u nder certain physiological conditions, namely, in the stationary phase of growth, in the presence of chloramphenicol in the growth medium, o r upon aeration in the absence of nutrients (starvation conditions). C ycloheximide prevented the appearance of cyanide-insensitive respirati on when the cells were aerated under starvation conditions. This fact suggested some form of induction involving de novo protein synthesis.