Molecular mechanisms of virus egress in haloarchaea

• Applicant: Dr. Tessa Quax
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Virology
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 464316632

Archaea are ubiquitous in the environment and thrive in diverse habitats ranging from the ocean to the human digestive tract. In archaea-dominated environments, more than half of the cells may be infected by viruses. Consequently, viruses represent an important evolutionary pressure on archaea. The viruses of archaea are distinct from viruses infecting bacteria and archaea, as they display an unusually high morphological diversity. Currently, only a hand-full of release mechanisms are known for the ~100 described archaeal viruses. Most bacterial viruses use the endolysin-holin system to disrupt the murein cell wall of their host. The egress mechanisms of archaeal viruses are likely to be very different, since archaea lack a murein cell wall. Some viruses can egress by budding of the host-cell, a process previously reported only for eukaryotic viruses. Other viruses rely on remarkable pyramidal-shaped egress structures. Both examples are from viruses infecting crenarchaea. However, the egress mechanisms of viruses infecting euryarchaea are still mysterious. This project aims to address how viruses egress from euryarchaeal cells. As a model, Haloferax gibbonsii LR2-5 will be used, as recently the first virus (HFTV1) infecting a member of the genus Haloferax was isolated from this host. Haloferax provides a distinct advantage for study of molecular infection mechanisms, due to well-developed genetics and the current availability of the first archaeal fluorescent fusion proteins. HFTV1 is a lytic virus and its egress mechanism will be studied with different light and electron microscopy techniques. In addition, protein players in this process will be identified by a combination of RNAseq, gene deletion, over-expression and protein interaction techniques. Other, recently identified LR2-5 infecting viruses, unrelated to HFTV1, will allow comparison between the egress mechanisms of different viruses infecting the same host species. This approach will enable a detailed characterization of molecular mechanisms underlying haloarchaeal viral egress and aid to understanding of infection strategies of archaeal viruses in general. It might allow for the identification of novel virus proteins specifically targeted at lysing archaeal cells. This project will thus contribute to increasing our understanding of viral diversity and evolution, and it will teach us how archaeal hosts can adapt to evolutionary pressure from viruses.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2330: New concepts in prokaryotic virus-host interactions - from single cells to microbial communities
• International Connection: Netherlands