A preparation method of specimens of the fungus Penicillium chrysogenum for ultrastructural and immuno-electron microscopical studies.

A combination of cryofixation without pre-treatment, freeze-substitution and low-temperature embedding was used to prepare specimens of Penicillium chrysogenum for electron microscopy. To produce specimens which are thin enough for appropriate cryofixation, the P.chrysogenum colonies were grown between dissected-dialysis tubing on an agar plate, which in addition allowed longitudinal sectioning. In contrast to classical chemical fixation, this preparation procedure resulted in excellent preservation of ultrastructure. Furthermore, the penicillin biosynthetic enzyme acyltransferase could be unequivocally located by immunogold labelling, indicating a preservation of antigenic properties of the specimen. Labelling density was not conspicuously affected when using different freeze-substitution media, but it was reduced after embedding in Epon 812.