Production of Lytic Plaques of Viral Origin in Penicillium

Abstract

THE presence of virus particles in fungi is now established on the basis of observations in Agaricus (Psalliota) bisporus and in Penicillium stoloniferum^2,3 and P. chrysogenum⁴. Viruses in A. bisporus cause several malformations of the fruiting body⁵ and some morphological variations of the colony in P. stoloniferum³. Small patches of white aerial mycelium have frequently been observed on the surface of fungi and we have confirmed this for P. citrinum and P. variabile grown on potato glucose agar at 24° C. When these organisms are grown on 18% lactose, 1% peptone, 2% agar, distilled water (pH 6·5) (medium A) at 24° C, lytic plaques are observed on the reverse of the patches of white aerial mycelium (Fig. 1a, b), which are morphologically similar to those produced by bacteriophages in bacteria and in streptomycetes. The mycelium taken from the centre of the lytic area consists of swollen hyphae, wholly lysed or with very little cytoplasm. Observation with the electron microscope, after fixation with phosphotungstate (PTA) at pH 7, has shown that the hyphae yield a large amount of virus particles (2 to 100 per field) as previously observed^1–4. The particles have a hexagonal shape, with no tail and a diameter of 400–500 Å.