Abstract
The Sulfolobus Spindle-shaped Virus (SSV) system has become a model for studying thermophilic virus biology, including archaeal host-virus interactions and biogeography. Several factors make the SSV system amenable to studying archaeal genetic mechanisms (e.g., CRISPRs) as well as virus-host interactions in high temperature acidic environments. Previously, we reported that SSVs exhibited differential infectivity on allopatric vs. sympatric hosts. We also noticed a wide host range for virus strain SSV9 (a.k.a., SSVK1). For decades, SSVs have been described as “non-lytic” double-stranded DNA viruses that infect species of the genus Sulfolobus and release virions via budding rather than host lysis. In this study, we show that SSVs infect hosts representing more than one genus of the family Sulfolobaceae in spot-on-lawn “halo” assays and in liquid culture infection assays. Growth curve analyses support the hypothesis that SSV9 virion release causes cell lysis. While SSV9 appears to lyse allopatric hosts, on a single sympatric host, SSV9 exhibits canonical non-lytic viral release historically reported SSVs. Therefore, the nature of SSV9 lytic-like behavior may be driven by allopatric evolution. The SSV9-infected host growth profile does not appear to be driven by multiplicity of infection (MOI). Greater stability of SSV9 vs. other SSVs (i.e., SSV1) in high temperature, low pH environments may contribute to higher transmission rates. However, neither higher transmission rate nor relative virulence in SSV9 infection seems to alter replication profile in susceptible hosts. Although it is known that CRISPR-Cas systems offer protection against viral infection in prokaryotes, CRISPRS are not reported to be a determinant of virus replication strategy. The mechanisms underlying SSV9 lytic-like behavior remain unknown and are the subject of ongoing investigations. These results suggest that genetic elements, potentially resulting from allopatric evolution, mediate distinct virus-host growth profiles of specific SSV-host strain pairings.
Highlights
In virology, reduced model systems are prokaryotic or single-cell eukaryotic viral systems that provide fundamental information regarding virus-host interactions and coevolution independent of the complexity found in macroorganisms with evolved immune systems
The Sulfolobus Spindle-shaped Virus (SSV) system has become a popular model for studying thermophilic archaeal virus biology and virus-host biogeography
To ensure that virus infection was a cause of host growth decline, presence of virus was determined by one of four distinct methods: electrospray ionization/mass spectrometry (ESI/MS) in units of virus particles per milliliter (VP mL−1); serial dilution plaque-like assays in units of halo-forming units per milliliter; virus-like particle (VLP) counts using transmission electron micrographs (VLP mL−1); and/or, quantitative polymerase chain reaction in terms of the total number of viral genomes per milliliter
Summary
In virology, reduced model systems are prokaryotic or single-cell eukaryotic viral systems that provide fundamental information regarding virus-host interactions and coevolution independent of the complexity found in macroorganisms with evolved immune systems. It is suggested that studying virus-host interactions in reduced model systems may provide opportunities to understand fundamental processes of virus evolution in host systems of agricultural or medical importance (Brockhurst et al, 2007; Dennehy, 2009). The Sulfolobus Spindle-shaped Virus (SSV) system has become a popular model for studying thermophilic archaeal virus biology and virus-host biogeography. Several factors make this system ideal for studying virus-host infections in crenarchaea (i.e., Sulfolobales). Given the wide geographical separation between sulfuric hot springs, which are habitats for SSVs and hosts, this system is amenable to studying multiple allopatric and sympatric virus-host pairs (Ceballos et al, 2012), which is essential for studying virus-host interactions, biogeography, and coevolution (Greischar and Koskella, 2007)
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