Archaeal viruses multiply: temporal screening in a solar saltern (original) (raw)
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An ssDNA virus infecting archaea: a new lineage of viruses with a membrane envelope
Molecular Microbiology, 2009
Archaeal organisms are generally known as diverse extremophiles, but they play a crucial role also in moderate environments. So far, only about 50 archaeal viruses have been described in some detail. Despite this, unusual viral morphotypes within this group have been reported. Interestingly, all isolated archaeal viruses have a double-stranded DNA (dsDNA) genome. To further characterize the diversity of archaeal viruses, we screened highly saline water samples for archaea and their viruses. Here, we describe a new haloarchaeal virus, Halorubrum pleomorphic virus 1 (HRPV-1) that was isolated from a solar saltern and infects an indigenous host belonging to the genus Halorubrum. Infection does not cause cell lysis, but slightly retards growth of the host and results in high replication of the virus. The sequenced genome (7048 nucleotides) of HRPV-1 is single-stranded DNA (ssDNA), which makes HRPV-1 the first characterized archaeal virus that does not have a dsDNA genome. In spite of this, similarities to another archaeal virus were observed. Two major structural proteins were recognized in protein analyses, and by lipid analyses it was shown that the virion contains a membrane. Electron microscopy studies indicate that the enveloped virion is pleomorphic (approximately 44 ¥ 55 nm). HRPV-1 virion may represent commonly used virion architecture, and it seems that structure-based virus lineages may be extended to non-icosahedral viruses.
Life, 2014
In hypersaline environments, haloarchaea (halophilic members of the Archaea) are the dominant organisms, and the viruses that infect them, haloarchaeoviruses are at least ten times more abundant. Since their discovery in 1974, described haloarchaeoviruses include head-tailed, pleomorphic, spherical and spindle-shaped morphologies, representing Myoviridae, Siphoviridae, Podoviridae, Pleolipoviridae, Sphaerolipoviridae and Fuselloviridae families. This review overviews current knowledge of haloarchaeoviruses, providing information about classification, morphotypes, macromolecules, life cycles, genetic manipulation and gene regulation, and host-virus responses. In so doing, the review incorporates knowledge from laboratory studies of isolated viruses, field-based studies of environmental samples, and both genomic and metagenomic analyses of haloarchaeoviruses. What emerges is that some haloarchaeoviruses possess unique morphological and life cycle properties, while others share features with other viruses (e.g., bacteriophages). Their interactions with hosts influence community structure and evolution of populations that exist in hypersaline environments as diverse as seawater evaporation ponds, to hot desert or Antarctic lakes. The discoveries of their wide-ranging and important roles in the ecology
Insights into Head-Tailed Viruses Infecting Extremely Halophilic Archaea
Journal of Virology, 2013
Extremophilic archaea, both hyperthermophiles and halophiles, dominate in habitats where rather harsh conditions are encountered. Like all other organisms, archaeal cells are susceptible to viral infections, and to date, about 100 archaeal viruses have been described. Among them, there are extraordinary virion morphologies as well as the common head-tailed viruses. Although approximately half of the isolated archaeal viruses belong to the latter group, no three-dimensional virion structures of these head-tailed viruses are available. Thus, rigorous comparisons with bacteriophages are not yet warranted. In the present study, we determined the genome sequences of two of such viruses of halophiles and solved their capsid structures by cryo-electron microscopy and three-dimensional image reconstruction. We show that these viruses are inactivated, yet remain intact, at low salinity and that their infectivity is regained when high salinity is restored. This enabled us to determine their t...
Global analysis of viral infection in an archaeal model system
Frontiers in microbiology, 2012
The origin and evolutionary relationship of viruses is poorly understood. This makes archaeal virus-host systems of particular interest because the hosts generally root near the base of phylogenetic trees, while some of the viruses have clear structural similarities to those that infect prokaryotic and eukaryotic cells. Despite the advantageous position for use in evolutionary studies, little is known about archaeal viruses or how they interact with their hosts, compared to viruses of bacteria and eukaryotes. In addition, many archaeal viruses have been isolated from extreme environments and present a unique opportunity for elucidating factors that are important for existence at the extremes. In this article we focus on virus-host interactions using a proteomics approach to study Sulfolobus Turreted Icosahedral Virus (STIV) infection of Sulfolobus solfataricus P2. Using cultures grown from the ATCC cell stock, a single cycle of STIV infection was sampled six times over a 72 h period...
Closely related archaeal Haloarcula hispanica icosahedral viruses
2012
Studies on viral capsid architectures and coat protein folds have revealed the evolutionary lineages of viruses branching to all three domains of life. A widespread group of icosahedral tailless viruses, the PRD1-adenovirus lineage, was the first to be established. A double -barrel fold for a single major capsid protein is characteristic of these viruses. Similar viruses carrying genes coding for two major capsid proteins with a more complex structure, such as Thermus phage P23-77 and haloarchaeal virus SH1, have been isolated. Here, we studied the host range, life cycle, biochemical composition, and genomic sequence of a new isolate, Haloarcula hispanica icosahedral virus 2 (HHIV-2), which resembles SH1 despite being isolated from a different location. Comparative analysis of these viruses revealed that their overall architectures are very similar except that the genes for the receptor recognition vertex complexes are unrelated even though these viruses infect the same hosts.
Journal of Virology, 2010
Only a few archaeal viruses have been subjected to detailed structural analyses. Major obstacles have been the extreme conditions such as high salinity or temperature needed for the propagation of these viruses. In addition, unusual morphotypes of many archaeal viruses have made it difficult to obtain further information on virion architectures. We used controlled virion dissociation to reveal the structural organization of Halorubrum pleomorphic virus 1 (HRPV-1) infecting an extremely halophilic archaeal host. The singlestranded DNA genome is enclosed in a pleomorphic membrane vesicle without detected nucleoproteins. VP4, the larger major structural protein of HRPV-1, forms glycosylated spikes on the virion surface and VP3, the smaller major structural protein, resides on the inner surface of the membrane vesicle. Together, these proteins organize the structure of the membrane vesicle. Quantitative lipid comparison of HRPV-1 and its host Halorubrum sp. revealed that HRPV-1 acquires lipids nonselectively from the host cell membrane, which is typical of pleomorphic enveloped viruses.
Structural and Functional Studies of Archaeal Viruses
Journal of Biological Chemistry, 2009
Viruses populate virtually every ecosystem on the planet, including the extreme acidic, thermal, and saline environments where archaeal organisms can dominate. For example, recent studies have identified crenarchaeal viruses in the hot springs of Yellowstone National Park and other high temperature environments worldwide. These viruses are often morphologically and genetically unique, with genomes that show little similarity to genes of known function, complicating efforts to understand their viral life cycles. Here, we review progress in understanding these fascinating viruses at the molecular level and the evolutionary insights coming from these studies.
Virion Architecture Unifies Globally Distributed Pleolipoviruses Infecting Halophilic Archaea
Journal of Virology, 2012
Our understanding of the third domain of life, Archaea, has greatly increased since its establishment some 20 years ago. The increasing information on archaea has also brought their viruses into the limelight. Today, about 100 archaeal viruses are known, which is a low number compared to the numbers of characterized bacterial or eukaryotic viruses. Here, we have performed a comparative biological and structural study of seven pleomorphic viruses infecting extremely halophilic archaea. The pleomorphic nature of this novel virion type was established by sedimentation analysis and cryo-electron microscopy. These nonlytic viruses form virions characterized by a lipid vesicle enclosing the genome, without any nucleoproteins. The viral lipids are unselectively acquired from host cell membranes. The virions contain two to three major structural proteins, which either are embedded in the membrane or form spikes distributed randomly on the external membrane surface. Thus, the most important step during virion assembly is most likely the interaction of the membrane proteins with the genome. The interaction can be driven by single-stranded or double-stranded DNA, resulting in the virions having similar architectures but different genome types. Based on our comparative study, these viruses probably form a novel group, which we define as pleolipoviruses.
Viral communities of two different salt pans located in the Namib Desert, Hosabes and Eisfeld, were investigated using a combination of multiple displacement amplification of metaviromic DNA and deep sequencing, and provided comprehensive sequence data on both ssDNA and dsDNA viral community structures. Read and contig annotations through online pipelines showed that the salt pans harbored largely unknown viral communities. Through network analysis, we were able to assign a large portion of the unknown reads to a diverse group of ssDNA viruses. Contigs belonging to the subfamily Gokushovirinae were common in both environmental datasets. Analysis of haloarchaeal virus contigs revealed the presence of three contigs distantly related with His1, indicating a possible new lineage of salterproviruses in the Hosabes playa. Based on viral richness and read mapping analyses, the salt pan metaviromes were novel and most closely related to each other while showing a low degree of overlap with other environmental viromes.