Host-dependent differences in replication and virion release strategy of the Sulfolobus Spindle-shaped Virus strain SSV9 (a.k.a., SSVK1): Lytic replication in hosts of the family Sulfolobaceae

The Sulfolobus Spindle-shaped Virus (SSV) system is a model for studying thermophilic archaeal virus biology. Several factors make the SSV system amenable to studying archaeal genetics and virus-host interactions in extreme environments. It has been shown that populations of Sulfolobus, the natural host, exhibit biogeographic structure. The acidic (pH<4.5) high temperature (65-88°C) habitats have low biodiversity, which diminishes prospects for host switch. SSVs and their hosts are readily cultured in liquid media and on plates. Given the wide geographic separation between various SSV-Sulfolobus habitats, the system is also amenable to studying allopatric versus sympatric virus-host interactions. We previously reported that SSVs exhibit differential infectivity on allopatric and sympatric hosts. We discovered a strikingly broad host-range for strain SSV9 (a.k.a., SSVK1). For decades, SSVs have been described as “non-lytic” dsDNA viruses that infect species of Sulfolobus and release virus particles via blebbing as a preferred strategy over host lysis (in reported laboratory infections). Here, we show, that SSVs infect more than one genus of the family Sulfolobaceae and, in allopatric hosts, SSV9 does not release virions via blebbing. Instead, SSV9 appears to lyse all susceptible allopatric hosts, while exhibiting canonical non-lytic virion release (historically reported for SSVs) on a single sympatric host. Lytic versus non-lytic virus release does not appear to be driven by multiplicity of infection. Data suggest that SSV9 is more stable than other SSVs in suspension; however, genetic substrates (e.g., CRISPR profiles) underlying non-lytic versus lytic virion release remain unresolved and are the subject of ongoing investigation.