5-bromodeoxyuridine-induced formation of virus-like particles in Naegleria Gruberi EGS

Abstract

Exposure of axenic cultures of the amoeboflagellate Naegleria gruberi EGs to the thymidine analogue 5-bromo-2′-deoxyuridine (BrdU) resulted in the induction of virus-like particles (VLP) and various structures associated with their development and presumed transmission. Previously, VLP induction could be accomplished only by growing amoebae in the presence of living bacteria as a food source. Addition of excess thymidine along with BrdU did not block induction of particles. This account demonstrates that the EGs-VLP system responded to BrdU as do a number of mammalian cell lines harbouring latent viruses, and provides the basis for future work on the infectivity of the VLPs for other amoebae as well as tissue culture cells.

The Relationships Between Protozoa and Viruses 2. Virus-Like Particles and Cytopathogenic Agent in Protozoa

“…By scrupulous electron-microscopy studies the authors established that VLPs can, first of all, be found in the nucleus of this protozoon. From there they move to the cytoplasm most probably through channels of nucleic membrane (Schuster, Dunnebacke, 1976). F. L. Schuster and T. H, Dunnebacke in their experiments with N. gruberi observed rupture of the nucleic membrane as it had been described by L. S. Diamond et al (1972) in E. histolytica when the filamentous virus was released from the nucleus.…”

“…The fact that VLPs in the axenic cultures of N. gruberi were observed neither in the nucleus nor in associating bodies in the cytoplasm brought F. L. Schuster (1969) to the thought that the formation of these particles might be induced with bacteria. Grounding on the results of further investigations F. L. Schuster and T. H. Dunnebacke (1976), how-ever, expressed an opinion that VLPs exist in the nucleus latently and become manifest simultaneously with associating bodies in the cytoplasm only after certain metabolic changes. It was established that the number of amoebae with VLPs depends upon the ratio of amoebae to bacteria, since after the decrease of the bacterial admixture in the medium the VLPs appeared at first in the nucleus of some amoebae only (ca in 5 per cent), but at the further decrease of the amount of bacteria the number of amoebae with VLPs began constantly growing, reaching even as much as 50 per cent in the culture.…”

“…Viruses in E. histolytica were established after purifying the culture from associating microflora, and VLPs in N. gruberi after transmission of cultures from axenic to monoxenic conditions. According to F. L. Schuster and T. H. Dunnebacke (1976) in both cases the changes in the nutrition and growth conditions were the necessary premise for manifestation of endobionts. The fact that VLPs in the axenic cultures of N. gruberi were observed neither in the nucleus nor in associating bodies in the cytoplasm brought F. L. Schuster (1969) to the thought that the formation of these particles might be induced with bacteria.…”

“…But after a detailed investigation they came to a conclusion that these formations were transmissive structures of VLPs in their moving to other individuals in the culture. According to F. L. Schuster and T. H. Dunnebacke (1976) there is a rather close dynamic relationship between the formation of VLPs in the nucleus and associating with them bodies in the cytoplasm of N. gruberi. The authors are of the opinion that most probably the VLPs migrating from nucleus to cytoplasm become surrounded by membraneous structures there, which, when getting mature become round and engulf the VLPs, thus separating the latter from the cytoplasm.…”

“…The formation or occurrence of VLPs was influenced also by other factors, whereas it was established that they appeared in the nucleus of amoebae even in axenic cultures when 5-bromodeoxyuridine had been added (Schuster, Dunnebacke, 1976;Schuster, Clemente, 1977). Thus the initial suggestion of F. L. Schuster's (1969) that the formation of these particles can be induced just with bacteria, which, most probably, play only the role of an inductor, was refuted.…”