Killer toxin secretion through the cell wall of the yeast Pichia anomala

A secreted killer toxin was detected through the cell wall of Pichia anomala cells by ultrastructural immunodetection with a specific monoclonal antibody (MAb KT4). MAb KT4 was successively detected by colloidal gold labeled streptavidin and biotinylated anti-mouse F(ab')(2) antibodies. The antigenic determinants of the toxin were localized throughout the cytoplasm and the cell wall of killer yeast cells. The Lowicryl K4M-immunogold method gave very satisfactory results and showed that the killer toxin was somewhat concentrated in the yeast cell wall layers before being exported into the medium. In agreement with previous reports, the binding of MAb KT4 suggested that the P. anomala killer toxin secretion did not result from a homogeneous diffusion across the yeast cell wall.