A giant virus infecting the amoeboflagellate Naegleria.

Giant viruses (Nucleocytoviricota) are significant lethality agents of various eukaryotic hosts. Although metagenomics indicates their ubiquitous distribution, available giant virus isolates are restricted to a very small number of protist and algal hosts. Here we report on the first viral isolate that replicates in the amoeboflagellate Naegleria. This genus comprises the notorious human pathogen Naegleria fowleri, the causative agent of the rare but fatal primary amoebic meningoencephalitis. We have elucidated the structure and infection cycle of this giant virus, Catovirus naegleriensis (a.k.a. Naegleriavirus, NiV), and show its unique adaptations to its Naegleria host using fluorescence in situ hybridization, electron microscopy, genomics, and proteomics. Naegleriavirus is only the fourth isolate of the highly diverse subfamily Klosneuvirinae, and like its relatives the NiV genome contains a large number of translation genes, but lacks transfer RNAs (tRNAs). NiV has acquired genes from its Naegleria host, which code for heat shock proteins and apoptosis inhibiting factors, presumably for host interactions. Notably, NiV infection was lethal to all Naegleria species tested, including the human pathogen N. fowleri. This study expands our experimental framework for investigating giant viruses and may help to better understand the basic biology of the human pathogen N. fowleri.

Proteomic analysis of Acanthamoeba castellanii response to Legionella pneumophila infection.

Legionella pneumophila is an opportunistic pathogen responsible for Legionnaires' disease or Legionellosis. This bacterium is found in the environment interacting with free-living amoebae such as Acanthamoeba castellanii. Until now, proteomic analyses have been done in amoebae infected with L. pneumophila but focused on the Legionella-containing vacuole. In this study, we propose a global proteomic analysis of the A. castellanii proteome following infection with L. pneumophila wild-type (WT) or with an isogenic ΔdotA mutant strain, which is unable to replicate intracellularly. We found that infection with L. pneumophila WT leads to reduced levels of A. castellanii proteins associated with lipid homeostasis/metabolism, GTPase regulation, and kinase. The levels of organelle-associated proteins were also decreased during infection. Legionellapneumophila WT infection leads to increased levels of proteins associated with polyubiquitination, folding or degradation, and antioxidant activities. This study reinforces our knowledge of this too little explored but so fundamental interaction between L. pneumophila and A. castellanii, to understand how the bacterium could resist amoeba digestion.