Decreased permeability as a mechanism of resistance to methyl benzimadazol-2-yl carbamate (MBC) in Sporobolomyces roseus.

Mutants of Sporobolomyces roseus resistant to benzimidazole fungicides varied in their responses to 2-(thiazol-4-yl) benzimidazole (thiabendazole, TBZ), methyl 1-(butylcarbamoyl)-benzimidazol-2-yl carbamate (benomyl) and methyl benzimidazol-2-yl carbamate (carbendazim, MCB). Incorporation of [14C] MBC into trichloroacetic acid extracts of the sensitive strain S4 increased during a 2 h incubation period, whereas incorporation into the resistant mutant M55 was unchanged. [14C] MBC uptake by S4 cells was five times higher than that by M55. MBC was identified as the main radioactive compound inside the S4 cells and reached a level of 2.4 mug/100 mg dry wt. The compound MBC enters the cells of Sp. roseus by a temperature-, energy-, pH- and concentration-dependent transport system which may be specific for compounds containing a benzimidazole nucleus. It is suggested that tolerance of M55 to MBC is due to decreased permeability of the cell to this compound.