New Insights into the Interaction of Free-Living Amoebae and Pandoravirus Inopinatum: Investigations of the Host Range and the Role of Multilamellar Bodies

FLA are predatory heterotrophic microorganisms, feeding as trophozoites on bacteria, cyanobacteria, fungi and algae while adhering to surfaces through phagocytosis. It is known that FLA produce and expel vesicles as part of the digestive process. Bacteria are packaged in multilamellar bodies and are released into the environment if not digested. In 2008, it was shown how easily the so-called Pandoraviruses can get in close contact with humans, while proliferating in Acanthamoeba.

In our study, the search for these packages and multilamellar bodies in Acanthamoebae was conducted by electron microscopy with special emphasis on Pandoravirus inopinatum virions being involved in these processes. The multilamellar bodies were detected within the trophozoites of the amoeba host strain and as expelled vesicles within their environment. Neither digested, partially digested or viable Pandoravirus inopinatum virions nor developmental stages were found within these packages. A modified host range evaluation method was used to study the uptake and the proliferation of Pandoravirus inopinatum virions by Acanthamoeba trophozoites via light microscopy and to determine the host range.

In addition to the Acanthamoeba strain, which was found to harbor Pandoravirus inopinatum initially, we confirmed another 9 Acanthamoeba strains to be susceptible, among them members of genotypes T4 and T 11.

The modified time series method, which we used, proved to be superior to the initial (more static) host range studies, in both axenic and xenic cultures.