Viruses are nonliving biological entities whose host range encompasses all known forms of life. They are deceptively simple in description (a protein shell surrounding genetic material with an ...occasional lipid envelope) and yet can infect all known forms of life. Recently, due to technological advancements, viruses from more extreme environments can be studied through both culture-dependent and independent means. Viruses with thermophilic, halophilic, psychrophilic, and barophilic properties are highlighted in this paper with an emphasis on the properties that allow them to exist in said environments. Unfortunately, much of this field is extremely novel and thus, not much is yet known about these viruses or the microbes they infect when compared to non-extremophilic host-virus systems. With this review, we hope to shed some light on these relatively new studies and highlight their intrinsic value.
Abstract The first archaeal virus was isolated over 40 years ago prior to the recognition of the three domain structure of life. In the ensuing years, our knowledge of Archaea and their viruses has ...increased, but they still remain the most mysterious of life׳s three domains. Currently, over 100 archaeal viruses have been discovered, but few have been described in biochemical or structural detail. However, those that have been characterized have revealed a new world of structural, biochemical and genetic diversity. Several model systems for studying archaeal virus–host interactions have been developed, revealing evolutionary linkages between viruses infecting the three domains of life, new viral lysis systems, and unusual features of host–virus interactions. It is likely that the study of archaeal viruses will continue to provide fertile ground for fundamental discoveries in virus diversity, structure and function.
Viruses have played a central role in the evolution and ecology of cellular life since it first arose. Investigations into viral molecular biology and ecological dynamics have propelled abundant ...progress in our understanding of living systems, including genetic inheritance, cellular signaling and trafficking, and organismal development. As well, the discovery of viral lineages that infect members of all three domains suggest that these lineages originated at the earliest stages of biological evolution. Research into these viruses is helping to elucidate the conditions under which life arose, and the dynamics that directed its early development. Archaeal viruses have only recently become a subject of intense study, but investigations have already produced intriguing and exciting results. STIV was originally discovered in Yellowstone National Park and has been the focus of concentrated research. Through this research, a viral genetic system was created, a novel lysis mechanism was discovered, and the interaction of the virus with cellular ESCRT machinery was revealed. This review will summarize the discoveries within this group of viruses and will also discuss future work.
Archaeal viruses are some of the most enigmatic viruses known, due to the small number that have been characterized to date. The number of known archaeal viruses lags behind known bacteriophages by ...over an order of magnitude. Despite this, the high levels of genetic and morphological diversity that archaeal viruses display has attracted researchers for over 45 years. Extreme natural environments, such as acidic hot springs, are almost exclusively populated by Archaea and their viruses, making these attractive environments for the discovery and characterization of new viruses. The archaeal viruses from these environments have provided insights into archaeal biology, gene function, and viral evolution. This review focuses on advances from over four decades of archaeal virology, with a particular focus on archaeal viruses from high temperature environments, the existing challenges in understanding archaeal virus gene function, and approaches being taken to overcome these limitations.
Recently it has been discovered that a number of eukaryotic viruses, including HIV, coopt the cellular Endosomal Sorting Complex Required for Transport (ESCRT) machinery to affect egress from ...infected cells. Strikingly, the ESCRT apparatus is conserved in a subset of Archaea, including members of the genus Sulfolobus where it plays a role in cytokinesis. In the current work, we reveal that the archaeal virus Sulfolobus turreted icosahedral virus isolated from Yellowstone National Park's acidic hot springs also exploits the host ESCRT machinery in its replication cycle. Moreover, perturbation of normal ESCRT function abrogates viral replication and, thus, prevents establishment of a productive Sulfolobus turreted icosahedral virus infection. We propose that the Sulfolobus ESCRT machinery is involved in viral assembly within the cytoplasm and in escape from the infected cell by using a unique lysis mechanism. Our results support an ancient origin for viruses “hijacking” ESCRT proteins to complete their replication cycle and thus identify a critical host–virus interaction conserved between two domains of life.
It is currently difficult to detect unknown viruses in any given environment. The recent discovery of CRISPR (clusters of regularly interspaced short palindromic repeats) loci within bacterial and ...archaeal cellular genomes may provide an alternative approach to detect new viruses. It has been shown that the spacer sequences between the direct repeat units of the CRISPR loci are often derived from viruses and likely function as guide sequences to protect the cell from viral infection. The spacer sequences within the CRISPR loci may therefore serve as a record of the viruses that have replicated within the cell. We have cataloged the CRISPR spacer sequences from cellular metagenomic data from high-temperature (>80°C), acidic (pH < 4) hot spring environments located in Yellowstone National Park (YNP). We designed a microarray platform utilizing these CRISPR spacer sequences as potential probes to detect viruses present in YNP hot spring environments. We show that this microarray approach can detect viral sequences directly from virus-enriched environmental samples, detecting new viruses which have not been previously characterized. We further demonstrated that this microarray approach can be used to examine temporal changes in viral populations within the environment. Our results demonstrate that CRISPR spacer sequence-based microarrays will be useful tools for detecting and monitoring viruses from diverse environmental samples.
The Archaea-and their viruses-remain the most enigmatic of life's three domains. Once thought to inhabit only extreme environments, archaea are now known to inhabit diverse environments. Even though ...the first archaeal virus was described over 40 years ago, only 117 archaeal viruses have been discovered to date. Despite this small number, these viruses have painted a portrait of enormous morphological and genetic diversity. For example, research centered around the various steps of the archaeal virus life cycle has led to the discovery of unique mechanisms employed by archaeal viruses during replication, maturation, and virion release. In many instances, archaeal virus proteins display very low levels of sequence homology to other proteins listed in the public database, and therefore, structural characterization of these proteins has played an integral role in functional assignment. These structural studies have not only provided insights into structure-function relationships but have also identified links between viruses across all three domains of life.
It is probably a biological constant that viruses are found associated with all known life and that they play an essential role in the ecology and evolution of all lifeforms. Lytic viruses have now ...been discovered that infect organisms from each of the three domains of life. Recently, a new lysis system has been described for two archaeal viruses. This lysis system appears to be novel and distinct from previously described virus-encoded lysis systems. A comparison of lytic viruses from each of the three domains may provide insights concerning the evolution of viruses.
Viruses are the largest reservoir of genetic material on the planet, yet little is known about the population dynamics of any virus within its natural environment. Over a 2-year period, we monitored ...the diversity of two archaeal viruses found in hot springs within Yellowstone National Park (YNP). Both temporal phylogeny and neutral biodiversity models reveal that virus diversity in these local environments is not being maintained by mutation but rather by high rates of immigration from a globally distributed metacommunity. These results indicate that geographically isolated hot springs are readily able to exchange viruses. The importance of virus movement is supported by the detection of virus particles in air samples collected over YNP hot springs and by their detection in metacommunity sequencing projects conducted in the Sargasso Sea. Rapid rates of virus movement are not expected to be unique to these archaeal viruses but rather a common feature among virus metacommunities. The finding that virus immigration rather than mutation can dominate community structure has significant implications for understanding virus circulation and the role that viruses play in ecology and evolution by providing a reservoir of mobile genetic material.
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