Virus ΨM2 enters a non-lytic lifecycle alternative to lysogeny during infection of Methanothermobacter marburgensis
Year: 2026
Type: preprint
Abstract: Methanogens, a diverse group of archaea that produce methane during energy metabolism, are prevalent in anoxic habitats where they are exposed to viral infections. The head-tailed virus ΨM2 is one of few virus isolates that infect a methanogen host and was described as a lytic virus that lyses its host, Methanothermobacter marburgensis . Here, we present evidence that ΨM2 does not exclusively follow the classic lytic lifecycle but can also enter an alternative, chronic infection-like state. Growth experiments showed that infected cultures in minimal medium, optimized for the methanogen host (MS medium) did not exhibit complete lysis but continuously released infective virions. In contrast, in a suboptimal complex medium (SAB medium), the ΨM2-infected culture released virions in the exponential growth phase and eventually lysed after 14 hours post infection. Although the genome of ΨM2 encodes a putative integrase, a prerequisite for lysogeny, whole genome sequencing of ΨM2-infected M. marburgensis cultures revealed that the viral DNA remained extrachromosomal rather than integrating into the host genome, likely due to a mutation in the integrase gene. These findings suggest that ΨM2 enters a non-lytic lifecycle alternative to lysogeny under suboptimal host growth conditions. Sequencing furthe identified a heterogeneous viral population including previously undescribed variants. A high density of non-synonymous mutations and frameshift-inducing insertions was observed within ORFs predicted to encode a capsid protein and a major spike protein, suggesting these viral variants to differ in host recognition and infectivity. Overall, our results show more complex viral behavior and greater genetic variability than previously described. Importance Methanogens directly contribute to global greenhouse gas emissions, but they can also be used to mitigate carbon dioxide emissions for biofuel production. Furthermore, they are increasingly recognized as important components of the human microbiota. Understanding the biology of viruses would greatly benefit climate change mitigation strategies as well as research on human gut methanogens. However, only few methanogenic viruses have been isolated to date. One reason might be that lysogeny, which entails viral integration in the genome of their methanogen host, is prevalent but not well understood, and thus, hinders the discovery of novel viruses. In support of this hypothesis, we provide evidence that an archaeal virus previously described as lytic presents an alternative non-lytic lifecycle, which hinders virus discovery through commonly employed lysis-based methods. Research on head-tailed methanogen viruses may provide insights into common features and potential evolutionary connections with the well-studied group of head-tailed bacteriophages.
Institutions: University of Tübingen, ETH Zurich, Leipzig University
Language: English
Subfield: Virology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7220926368