Unveiling Cell Surface and Type IV Secretion Proteins Responsible for Archaeal Rudivirus Entry

Abstract

Sulfolobus mutants resistant to archaeal lytic virus Sulfolobus islandicus rod-shaped virus 2 (SIRV2) were isolated, and mutations were identified in two gene clusters, cluster sso3138 to sso3141 and cluster sso2386 and sso2387, encoding cell surface and type IV secretion proteins, respectively. The involvement of the mutations in the resistance was confirmed by genetic complementation. Blocking of virus entry into the mutants was demonstrated by the lack of early gene transcription, strongly supporting the idea of a role of the proteins in SIRV2 entry.T o date, relatively few archaeal viruses have been characterized, and most of those that have been characterized infect acidothermophilic members of the order Sulfolobales. Despite their limited number of around 50 species, they exhibit considerably greater morphological diversity than the more extensively characterized bacteriophages, about 95% of which show head-tail morphologies. Archaeal viruses, in contrast, exhibit fusiform shapes, often with one or two tails, bottle shapes, bearded-globular forms, and a wide variety of rod-like and filamentous morphotypes which often carry small terminal appendages (1-3). This morphological diversity suggests that the archaeal viruses may employ a variety of mechanisms to enter their hosts, but current insights into entry mechanisms are limited to an OppA transporter protein, Sso1273, possibly providing a receptor site for the Acidianus two-tailed virus (ATV) in Sulfolobus solfataricus P2 (4). And very recently, microscopic studies suggested that Sulfolobus islandicus rod-shaped virus 2 (SIRV2) enters the host cell by attaching and moving through a pilus-like filament; however, the nature of the structure and the identity of the involved proteins remain elusive (5).Sulfolobus solfataricus P2 is an acidothermophilic crenarchaeon that can host a wide range of archaeal viruses, many of which are propagated stably (1, 3, 6). Moreover, few of the viruses appear to induce cell lysis, possibly reflecting a need to minimize contact with the harsh hot acidic environment. However, recent studies have identified a few viruses that can enter a lytic phase, including the Sulfolobus turreted icosahedral virus (STIV), the two-tailed fusiform (ATV), and, more recently, the rudivirus SIRV2 (7-9).SIRV2 is classified in the family Rudiviridae together with other well-characterized viruses, including SIRV1 (10, 11), ARV1 (12) and SRV1, (13), all of which are rod shaped and lack an envelope, and their genomes consist of linear double-stranded DNA with covalently closed ends (10,14,15). In a recent microarray analysis of S. solfataricus infected with SIRV2, we demonstrated that the viral genes were activated at different times and that mainly stressresponse host genes and those implicated in vesicle formation were downregulated (16). The results also illustrated that SIRV2 infection at a multiplicity of infection (MOI) of 30 resulted in growth inhibition of S. solfataricus 5E6 (16). In the present experiment, the culture was infected at a lower...

Formation of a Viral Replication Focus in Sulfolobus Cells Infected by the Rudivirus Sulfolobus islandicus Rod-Shaped Virus 2

“…The resulting PCR product was cloned into the NdeI and StuI sites of plasmid pEXA2 (30) to generate pEXA2-TK, where the tk gene is under the control of an inducible arabinose promoter. pEXA2-TK was electroporated into S. solfataricus Sens1 (28), and transformants were selected on SCVY plates and screened by PCR. One colony was grown in liquid medium and labeled strain SsoTK.…”

40 Years of archaeal virology: Expanding viral diversity

“…In particular, we know little of virus entry, assembly, and of the role of host components involved in archaeal virus replication cycles. Recent studies indicate that SIRV attachment and likely virion DNA entry into its host is via attachment to the host's pili (Deng et al, 2014a), in a mechanism that may mimic bacteriophage. Furthermore, we may uncover novel proteins and/or pathways that have as of yet to be discovered.…”

Differentiation and Structure in Sulfolobus islandicus Rod-Shaped Virus Populations

“…SIRVs belong to the Rudiviridae family and to date, only two SIRV isolates from Iceland, SIRV1 and SIRV2, have been characterized [20,21,22,23,24] and established as a model system for studying host-virus interactions in the laboratory [22,25,26]. The virions of SIRV2, the type member of the family, are non-enveloped, stiff rods that measure approximately 23 nm × 900 nm [20].…”