Biology subjects

Schwarzer, S.

Publications and source records attributed to Schwarzer, S..

4 recordsLinked to original sources

bioRxiv2026

A Tripartite Co-culture System Reveals Defensive Mutualism Between a Nanobdellati Symbiont and Its Host

Archaeal symbioses remain among the least understood cellular interactions. Ultra-small Nanobdellati (initially called DPANN) archaea rely on larger hosts for survival, yet their effects on host eco-physiology and their interactions with infecting viruses have not yet been examined experimentally. Here, we established the first stable tripartite co-culture comprising a Nanobdellales symbiont (YN4), its archaeal host (YN4HA), and a virus (MTIV4). We analyzed this system using physiological, genomic, transcriptomic, glycoproteomic, and cryo-electron tomography (cryoET) approaches. CryoET analysis revealed that the Nanobdellales archaeon formed cone-like structures to contact the host, as has been observed in other Nanobdellati-host systems. In this system, the host is infected by the virus. The Nanobdellales archaeon mitigated virus-induced growth inhibition of the host without any detectable fitness cost, indicating a defensive mutualism rather than a strictly parasitic relationship. This protective effect may involve Nanobdellati-driven remodeling of host cell surface glycans, suggesting a previously unrecognized glycan-mediated defense strategy. Overall, our tripartite system provides new insight into complex archaeal interactions in extreme environments that cannot be captured through conventional binary co-culture systems.

microbiology↗

bioRxiv2025

The infection cycle of the haloarchaeal virus HFTV1 is tightly regulated and strongly inhibits motility of its host

Although viruses have been shown to infect all domains of life, our understanding of the genetic program behind the exploitation of host resources to produce progeny virions is thus far limited to several bacterial viruses. Therefore, to elucidate the transcriptome of euryarchaeal viruses and their hosts, we employed RNAseq analysis of samples taken at different time points from Haloferax gibbonsii LR2-5 cultures infected with the lytic model virus Haloferax Tailed Virus 1 (HFTV1). While following the transcription of viral genes throughout the infective life cycle, we observed a tight temporal regulation of viral transcripts as well as differential expression from within viral gene clusters. Furthermore, anti-sense RNAs (asRNAs) appear to play an important role in support of the timing of late-expressed viral genes. Therefore, with many differentially expressed transcripts, including intragenic transcripts and asRNAs, the regulatory machinery employed by HFTV1 contrasts with viral model systems (based on phages), in which antitermination and/or alternative polymerases (seemingly lacking in HFTV1) are more widespread. When looking into differentially expressed host genes, we observed a strong downregulation of genes involved in motility, such as the archaellum and chemotaxis machinery, which was confirmed with swimming assays of HFTV1 infected cells. This might be a strategy of the virus to redirect energy flowing into movement towards the production of virions. In conclusion, this work thus provides a stepping stone for further exploration of the intriguing strategies of viral transcriptional regulation of their infection cycle across the domains of life. IMPORTANCEViruses infect members of all three domains of life, including Archaea. Euryarchaea are widespread microorganisms found in various environments such as the human gut and solar salterns. Due to the exceptional availability of cell biology and genetic tools of some salt-loving archaea, they are a model system to extrapolate from. Insights into the regulation of viral infections are of particular importance, especially since HFTV1, has been adopted as a model virus by the archaeal viral community. We found that, while harboring parallels with bacterial viruses, such as tight temporal regulation, HFTV1 harbors an impressive number of differentially expressed transcriptional units. Furthermore, anti-sense RNAs and intragenic regulatory elements seem to play a much more prominent role in HFTV1 gene expression. Thus, this work challenges current models and provides valuable new insights into the gene regulation of viral infection of archaea, which mark similarities and differences with viruses from other domains of life.

microbiology↗

bioRxiv2024

Cryo-EM resolves the structure of the archaeal dsDNA virus HFTV1 from head to tail

Outnumbering their hosts by at least a factor of 10, viruses are the most common biological entity on Earth, are major drivers of evolution, and greatly impact on the dynamics of our planets ecosystems. While viruses infecting bacteria and eukaryotes have been extensively studied, the viruses roaming the archaeal domain remain largely unexplored. In recent years, a growing number of archaeal viruses have been described, revealing a stunningly diverse range of morphologies that appear unique to archaea. Detailed structural studies are paramount to fully understand how archaeal viruses infect their hosts. However, no complete atomic models of archaeal viruses are available to date. Using electron cryo-microscopy, we investigated the structure of the archaeal virus Haloferax tailed virus 1 (HFTV1), which infects the halophile Haloferax gibbonsii LR2-5 originating from the Senegalese salt lake Retba. Through single particle analysis, we achieved near-atomic resolution for the entire set of HFTV1s structural proteins, enabling the building of a full atomic model of the virion. Comparing the structures of DNA filled and empty capsids, we visualise structural changes occurring upon DNA ejection. By investigating the double-stranded DNA inside the capsid, we elucidate how the genome is spooled upon loading. Furthermore, our structure reveals putative cell-surface receptor-binding and catalytic roles of capsid turret, baseplate, and tail fibre proteins. Together, our data provide new insights into the mechanisms of HFTV1 assembly and infection, unveiling new perspectives on general rules of host-virus interactions in archaea and their evolutionary links to bacterial and eukaryotic viruses.

microbiology↗

bioRxiv2020

Cellular and genomic properties of Haloferax gibbonsii LR2-5, the host of euryarchaeal virus HFTV1

Hypersaline environments are the source of many viruses infecting different species of halophilic euryarchaea. Information on infection mechanisms of archaeal viruses is scarce, due to the lack of genetically accessible virus-host models. Recently a new archaeal siphovirus, Haloferax tailed virus 1 (HFTV1), was isolated together with its host belonging to the genus Haloferax, but it is not infectious on the widely used model euryarcheon Hfx. volcanii. To gain more insight into the biology of HFTV1 host strain LR2-5, we studied characteristics that might play a role in its virus susceptibility: growth-dependent motility, surface layer, filamentous surface structures and cell shape. Its genome sequence showed that LR2-5 is a new strain of Hfx. gibbonsii. LR2-5 lacks obvious viral defense systems, such as CRISPR-Cas, and the composition of its cell surface is different from Hfx. volcanii, which might explain the different viral host range. This work provides first deep insights into the relationship between the host of halovirus HFTV1 and other members of the genus Haloferax. Given the close relationship to the genetically accessible Hfx. volcanii, LR2-5 has high potential as a new model for virus-host studies in euryarchaea.

microbiology↗