Project description:Legionella pneumophila are important opportunistic pathogens for which environmental reservoirs such as protists are crucial for the infection of humans. Free-living amoebae are considered key hosts providing nutrients and shelter for highly efficient intracellular proliferation of L. pneumophila, which eventually leads to lysis of the amoeba host cell. Yet, the significance of other bacterial players for L. pneumophila ecology is poorly understood. In this study we used a ubiquitous amoeba and their bacterial endosymbiont to investigate the impact of this common association on L. pneumophila infection. We demonstrate that Acanthamoeba castellanii harboring the chlamydial symbiont Protochlamydia amoebophila were able to erase L. pneumophila and, in contrast to symbiont-free amoebae, survived the infection and were able to resume growth. Environmental amoeba isolates harboring P. amoebophila were equally well-protected, and fresh environmental isolates of L. pneumophila were equally well-erased, suggesting ecological relevance of this symbiont-mediated protection. We further show that protection was not mediated by impaired L. pneumophila uptake. Instead, we observed reduced virulence of L. pneumophila released from symbiont-containing amoebae that is strongly supported by transcriptome data. Interference with transition to the transmissive phase is thus likely the basis for this protection. Finally, our data indicate that the defensive response of amoebae harboring P. amoebophila leaves the amoebae with superior fitness reminiscent of immunological memory. Given that mutualistic associations between bacteria and amoebae are widely distributed, P. amoebophila and potentially other amoeba endosymbionts could be key elements in shaping environmental survival, abundance and virulence of this important pathogen thereby affecting frequency of human infection.
Project description:Giant viruses are extraordinary members of the virosphere due to their structural complexity and high diversity in gene content. Haptophytes are ecologically important primary producers in the ocean, and all known viruses that infect haptophytes are giant viruses. Our in-depth electron microscopic, phylogenomic and virion proteomic analyses of two haptophyte-infecting giant viruses, Haptolina ericina virus RF02 (HeV RF02) and Prymnesium kappa virus RF02 (PkV RF02), unravel their large capacity for host manipulation and arsenals that functions during the infection cycle from virus entry to release. The virus infection induces significant morphological changes of host cell that are manipulated to build a virus proliferation factory. Both viruses’ genomes encode a putative nucleoprotein (dinoflagellate/viral nucleoprotein; DVNP), which was also found in the virion proteome of PkV RF02. Phylogenetic analysis suggests that DVNPs are widespread in marine giant metaviromes. Furthermore, the analysis shows that the dinoflagellate homologues were possibly acquired from viruses of the order Imitervirales.
Project description:High resolution Mass Spectrometry and Peptides identification uncovered ancestral giant insect viruses motifs within Histone-4 peptides in human liver cells. These peptides did not match any human sequence. This finding consolidates the dogma that molecular patterns are universal and suggests that metazoan cellular structures possibly share an evolutionary link with ancient giant viruses.
Project description:Nested parasitic chains are common schemes in nature, not limited to cellular organisms. Some giant viruses infecting protists are hyperparasitized by smaller viruses named virophages. Both can carry episomal plasmid-like DNA molecules known as transpovirons in their particles. They all share common transcriptional regulatory elements dictating the expression of their genes, which are transcribed within viral factories built by giant viruses in the host cytoplasm. This suggests close but as yet undetermined interactions between their respective transcriptional networks. Here, we studied the protein content of Megavirus chilensis virions produced in Acanthamoeba castellanii cells co-infected or not with the virophage Zamilon vitis.
Project description:Latency is a common strategy in a wide range of viral lineages, but its prevalence in giant viruses remains unknown. Here we describe the activity and viral production from a 617 kbp integrated giant viral element in the model green alga Chlamydomonas reinhardtii. We resolve the integrated viral region using long-read sequencing and show that viral particles are produced and released in otherwise healthy cultures. A diverse array of viral-encoded selfish genetic elements are expressed during GEVE reactivation and produce proteins that are packaged in virions. In addition, we show that field isolates of Chlamydomonas sp. harbor latent giant viruses related to the C. reinhardtii GEVE that exhibit similar infection dynamics, demonstrating that giant virus latency is prevalent in natural host communities. Our work reports the largest temperate virus documented to date and the first active GEVE identified in a unicellular eukaryote, substantially expanding the known limits of viral latency.