Experimental co-infection of Saccamoeba lacustris with Mimivirus-like Giant virus and a small Satellite virus

Two Mimivirus-like giant viruses were isolated independently from each other from the same plane tree (Platanus occidentalis). The first isolate KSL5 was discovered within its natural host Saccamoeba strain SL5 and was associated with a small icosahedral satellite virus. The phylogenetic analysis of the host amoeba revealed a close relatedness of the 18S rRNA gene to Saccamoeba lacustris. The second giant virus KSL5x was isolated using the virus free S. lacustris strain SL5 as bait. Interestingly KSL5x did not show any affiliation with a satellite virus. Association experiments of the satellite virus with the KSL5x infected host cells resulted in a co-infection of the S. lacustris strain SL5 indicating that the satellite virus could multiply in coexistence with giant virus KSL5x as well. However challenging S. lacustris SL5 with only the satellite virus did not lead to any visible infection of the host cells or the multiplication of the virus. We therefore conclude a strong dependency of the satellite virus on the virus factory of KSL5. Evaluations of the host range of KSL5 showed that only two of three S. lacustris strains were susceptible to the new giant virus KSL5 indicating a highly species-specific virus-virophage system in S. lacustris. As suggested by Hauröder et al. (2017) we propose the name Platanovirus saccamoebae for the new Mimivirus-like giant virus KSL5.