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Papers by Kenneth Stedman

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The Sulfolobus Spindle-shaped Virus (SSV) system is a model for studying thermophilic archaeal vi... more 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 relea...

ABSTRACTThe Sulfolobus Spindle-shaped Virus (SSV) system has become a model for studying thermoph... more ABSTRACTThe 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. First, it has been shown that endemic populations of Sulfolobus, the reported SSV host, exhibit biogeographic structure. Second, the acidic (pH<4.5) high temperature (65-88°C) SSV habitats have low biodiversity, thus, diminishing opportunities for host switching. Third, SSVs and their hosts are readily cultured in liquid media and on gellan gum plates. Fourth, given the wide geographic separation between the various SSV-Sulfolobus habitats, the system is amenable for studying allopatric versus sympatric virus-host interactions. Previously, we reported that SSVs exhibit differential infectivity on allopatric and sympatric hosts. We ...

Genes, Jan 8, 2017

Viruses with spindle or lemon-shaped virions are rare in the world of viruses, but are common in ... more Viruses with spindle or lemon-shaped virions are rare in the world of viruses, but are common in viruses of archaeal extremophiles, possibly due to the extreme conditions in which they thrive. However, the structural and genetic basis for the unique spindle shape is unknown. The best-studied spindle-shaped virus, Sulfolobus Spindle-shaped Virus 1 (SSV1), is composed mostly of the major capsid protein VP1. Similar to many other viruses, proteolytic cleavage of VP1 is thought to be critical for virion formation. Unlike half of the genes in SSV1, including the minor capsid protein gene VP3, the VP1 gene does not tolerate deletion or transposon insertion. To determine the role of the VP1 gene and its proteolysis for virus function, we developed techniques for site-directed mutagenesis of the SSV1 genome and complemented deletion mutants with VP1 genes from other SSVs. By analyzing these mutants, we demonstrate that the N-terminus of the VP1 protein is required, but the N-terminus, or en...

Journal of Photochemistry

Journal of Virological Methods

Characterizing virus-host relationships is critical for understanding the impact of a virus on an... more Characterizing virus-host relationships is critical for understanding the impact of a virus on an ecosystem, but is challenging with existing techniques, particularly for uncultivable species. We present a general, cultivation-free approach for identifying phageassociated bacterial cells. Using PCR-activated cell sorting, we interrogate millions of individual bacteria for the presence of specific phage nucleic acids. If the nucleic acids are present, the bacteria are recovered via sorting and their genomes analyzed. This allows targeted recovery of all possible host species in a diverse population associated with a specific phage, and can be easily targeted to identify the hosts of different phages by modifying the PCR primers used for detection. Moreover, this technique allows quantification of free phage particles, as benchmarked against the "gold standard" of virus enumeration, the plaque assay.

Biology and Technology at High Temperatures, 2007

... furiosus, Sulfolobus[57] acidocaldarius pAG1, 2and21 pGT5 Pyrococcus furiosus, Sulfolobus ad... more ... furiosus, Sulfolobus[57] acidocaldarius pAG1, 2and21 pGT5 Pyrococcus furiosus, Sulfolobus adh[13] acidocaldarius pYS2 pGT5 Pyrococcus abyssi pyrE[18] pEXSs SSV1* Sulfolobus solfataricus hph, adh, lacS[12, 25, 71, 74] poriC-hphT S. so oriC Sulfolobus solfataricus ...

To date there is no known evidence of viruses within the rock record. Their small size and absenc... more To date there is no known evidence of viruses within the rock record. Their small size and absence of a metabolism has led to the hypothesis that they lack unique biological signatures, and the potential to become preserved. Biosignature research relevant to early Earth has focused on prokaryotic communities; however, the most abundant member of modern ecosystems, viruses, have been ignored. In order to establish a baseline for research on virus biosignatures, we have initiated laboratory research on known lipid-containing viruses. PRD1 is a lipid-containing virus that infects and replicates in Salmonella typhimurium LT2. PRD1 is a 65 nm spherical virus with an internal lipid membrane, which is a few nanometers thick. When the PRD1 virus stock was mixed with a 400 ppm SiO2 (final concentration) solution and incubated for six months. Fourier Transform Infrared Spectroscopy and lipid analysis using gas chromatography revealed that the virus lipids were still detectable despite complet...

The preservation potential of lipid-containing viruses, PRD1 and PBCV1, within silicifying soluti... more The preservation potential of lipid-containing viruses, PRD1 and PBCV1, within silicifying solutions exists. Both viruses are rapidly removed from precipitating solutions, and the lipids within PBCV1 are unique from that of their host.

An alternative epifluorescence microscopy (EFM) technique for virus enumeration has been develope... more An alternative epifluorescence microscopy (EFM) technique for virus enumeration has been developed using polycarbonate Track Etch (PCTE) filter membranes in place of aluminum oxide Anodisc membranes. The established EFM technique, first developed by Hennes and Suttle in 1995 and later expanded upon by Noble and Fuhrman in 1998, uses supported 20 nm pore-size Anodisc filter membranes to determine virus abundance in natural environments. Increased price and sporadic availability of Anodisc filters stimulated the evaluation of alternative filters for use in the procedure. The feasibility of using 30 nm pore-size PCTE filters for virus enumeration was assessed using the Anodisc filter procedure as a control. Although virion particle counts are slightly less precise using PCTE filters, they offer a substitute for Anodiscs while requiring only minor adjustments to the established protocol. Per slide, the PCTE costs approximately ten times less to prepare than the Anodisc-based method. ABB...

Journal of bacteriology, 1993

Frontiers in microbiology, 2012

Viruses of thermophilic Archaea are unique in both their structures and genomic sequences. The mo... more Viruses of thermophilic Archaea are unique in both their structures and genomic sequences. The most widespread and arguably best studied are the lemon-shaped fuselloviruses. The spindle-shaped virus morphology is unique to Archaea but widespread therein. The best studied fusellovirus is SSV1 from Beppu, Japan, which infects Sulfolobus solfataricus. Very little is known about the function of the genes in the SSV1 genome. Recently we have developed genetic tools to analyze these genes. In this study, we have deleted three SSV1 open reading frames (ORFs) ranging from completely conserved to poorly conserved: VP2, d244, and b129. Deletion of the universally conserved ORF b129, which encodes a predicted transcriptional regulator, results in loss of infectivity. Deletion of the poorly conserved predicted DNA-binding protein gene VP2 yields viable virus that is indistinguishable from wild-type. Deletion of the well-conserved ORF d244 that encodes a predicted nuclease yields viable virus. H...

Genetics, 1999

Directed open reading frame (ORF) disruption and a serial selection technique in Escherichia coli... more Directed open reading frame (ORF) disruption and a serial selection technique in Escherichia coli and the extremely thermophilic archaeon Sulfolobus solfataricus allowed the identification of otherwise cryptic crucial and noncrucial viral open reading frames in the genome of the archaeal virus SSV1. It showed that the 15. 5-kbp viral genome can incorporate a 2.96-kbp insertion without loss of viral function and package this DNA properly into infectious virus particles. The selection technique, based on the preferential binding of ethidium bromide to relaxed DNA and the resulting inhibition of endonuclease cleavage to generate a pool of mostly singly cut molecules, should be generally applicable. A fully functional viral shuttle vector for S. solfataricus and E. coli was made. This vector spreads efficiently through infected cultures of S. solfataricus, its replication is induced by UV irradiation, it forms infectious virus particles, and it is stable at high copy number in both S. s...

Molecular Microbiology, 2003

Sulfolobus solfataricus has developed into an important model organism for molecular and biochemi... more Sulfolobus solfataricus has developed into an important model organism for molecular and biochemical studies of hyperthermophilic archaea. Although a number of in vitro systems have been established for the organism, efficient tools for genetic manipulations have not yet been available for any hyperthermophile. In this work, we have developed a stable and selectable shuttle vector based on the virus SSV1 of Sulfolobus shibatae. We have introduced pUC18 for propagation in Escherichia coli and the genes pyrEF coding for orotidine-5&amp;amp;amp;amp;amp;amp;amp;amp;#39;-monophosphate pyrophosphorylase and orotidine-5&amp;amp;amp;amp;amp;amp;amp;amp;#39;-monophosphate decarboxylase of Sulfolobus solfataricus as selectable marker to complement pyrimidine auxotrophic mutants. Furthermore, the beta-galactosidase gene (lacS) was introduced into this vector as a reporter under the control of the strong and heat-inducible promoter of the Sulfolobus chaperonin (thermosome). After transformation of a S. solfataricus pyrEF/lacS double mutant, the vector was found to reside as a single-copy vector, stably integrated into the host chromosome via the site-specific recombination system of SSV1. Specific beta-galactosidase activities in transformants were found to be fourfold higher than in wild-type S. solfataricus cells, and increased to more than 10-fold after heat shock. Greatly increased levels of lacS mRNA were detected in Northern analyses, demonstrating that this reporter gene system is suitable for the study of regulated promoters in Sulfolobus and that the vector can also be used for the high-level expression of genes from hyperthermophilic archaea.

The Springer Index of Viruses, 2011

Encyclopedia of Virology, 2008