Biology subjects

Papke, R. T.

Publications and source records attributed to Papke, R. T..

8 recordsLinked to original sources

bioRxiv2024

A new archaeal virus that suppresses the transcription of host immunity genes

In some extreme environments, archaeal cells have been shown to have chronic viral infections, and such infections are well-tolerated by the hosts and may potentially protect against more lethal infections by lytic viruses. We have discovered that a natural Haloferax strain (48N), which is closely related to the model organism Haloferax volcanii, is chronically-infected by a lemon-shaped virus, which we could purify from the medium. The chronic infection by this virus, which we named LSV-48N, is never cleared, despite the multiple defense systems of the host that include CRISPR-Cas, and two CBASS systems. Curing 48N of its virus by genetic engineering, led to radical changes in the gene expression profile of 48N and a dramatic improvement in its growth rate. Remarkably, the cured 48N is the fastest-growing haloarchaeon reported to date, with a generation time of approximately 1 hour at 45{degrees}C compared to the typical 2.5 hours of H. volcanii or its infected isogen, and faster than any known haloarchaeon. The virus subverts host defenses by reducing their transcription and interfering with the CRISPR spacer acquisition machinery. Our results suggest that the slow growth of many halophilic archaea could be due to the effects of proviruses within their genomes that consume resources and alter the gene expression of their hosts.

microbiology↗

bioRxiv2023

Using the pan-genomic framework for the discovery of genomic islands in the haloarchaeon Halorubrum ezzemoulense

In this study, we use pan-genomics to characterize the organized variability from the widely dispersed halophilic archaeal species Halorubrum ezzemoulense. We include a multi-regional sampling of newly sequenced, high-quality draft genomes. Using the pan-genome graph of the species, we discover 50 genomic islands which represent rare accessory genetic capabilities available to members of the species. 19 of these islands are likely the remnant of mobile genetic elements and are enriched for genomic dark matter. 10 islands encode for niche adapting solute transporters, with a cosmopolitan but limited distribution throughout the strains. We also observe rearrangements which have led to the insertion/recombination/replacement of mutually exclusive genomic islands in equivalent genome positions ("homeocassettes"). These conflicting islands encode for similar functions, but homologs from islands located between the same core genes exhibit extreme divergence on the amino acid level. Homeocasettes provide variations for a homologous function, which may confer a greater range of adaptability to the species group. We observe some islands that appear geographically restricted; however, we also observe the coexistence of genomes, in a single geographic region, with and without certain genomic islands, demonstrating the retention and spread of rare genes in the pan-genome. ImportanceUnderstanding the evolution of genome content is a key puzzle in evolutionary biology. Despite its importance, this area hasnt received thorough investigation. This is especially true of Archaeal organisms, which constitute a large fraction of Earths diversity, but are often referred to as the "forgotten" or "third" domain of life. This study dives into those questions by finding rare genes amongst a group of closely related Archaeal species, and describes how their transfer, utilization and persistence may contribute to the speciation and specialization of the group.

microbiology↗

bioRxiv2020

Nutrient supplementation experiments on saltern microbial communities support utilization of DNA as a source of phosphorus

All environments including hypersaline ones harbor measurable concentrations of dissolved extracellular DNA (eDNA) that can be utilized by microbes as a nutrient. However, it remains poorly understood which eDNA components are used, and who in a community utilizes it. For this study, we incubated a saltern microbial community with combinations of carbon, nitrogen, phosphorus, and DNA, and tracked the community response in each microcosm treatment via 16S rRNA and rpoB gene sequencing. We show that microbial communities used DNA only as a phosphorus source, and provision of other sources of carbon and nitrogen was needed to exhibit a substantial growth. The taxonomic composition of eDNA in the water column changed with the availability of inorganic phosphorus or supplied DNA, hinting at preferential uptake of eDNA from specific organismal sources. Especially favored for growth was eDNA from the most abundant taxa, suggesting some haloarchaea prefer eDNA from closely related taxa. Additionally, microcosms composition shifted substantially depending on the provided nutrient combinations. These shifts allowed us to predict supplemented nutrients from microbial composition with high accuracy, suggesting that nutrient availability in an environment could be assessed from a taxonomic survey of its microbial community.

microbiology↗

bioRxiv2020

Insights into gene expression changes under conditions that facilitate horizontal gene transfer (mating) of a model Archaeon

Horizontal gene transfer is a means by which bacteria, archaea, and eukaryotes are able to trade DNA within and between species. While there are a variety of mechanisms through which this genetic exchange can take place, one means prevalent in the archaeon Haloferax volcanii involves the transient formation of cytoplasmic bridges between cells and is referred to as mating. This process can result in the exchange of very large fragments of DNA between the participating cells. Genes governing the process of mating, including triggers to initiate mating, mechanisms of cell fusion, and DNA exchange, have yet to be characterized. We used a transcriptomic approach to gain a more detailed knowledge of how mating might transpire. By examining the differential expression of genes expressed in cells harvested from mating conditions on a filter over time and comparing them to those expressed in a shaking culture, we were able to identify genes and pathways potentially associated with mating. These analyses provide new insights into both the mechanisms and barriers of mating in Hfx. volcanii.

microbiology↗

bioRxiv2020

The Impact of Restriction-Modification Systems on Mating in Haloferax volcanii

Halobacteria have been observed to be highly recombinogenic, frequently exchanging genetic material. Several barriers to mating in the Halobacteria have been examined, such as CRISPR-Cas, glycosylation, and archaeosortases, but these are low barriers that do not drastically reduce the recombination frequency. Another potential barrier could be restriction-modification (RM) systems, which cleave DNA that is not properly methylated, thus limiting the exchange of genetic material between cells which do not have compatible RM systems. In order to examine the role of RM systems on limiting recombination in the Halobacteria, the impact of RM systems on cell-to-cell mating in Haloferax volcanii, a well-characterized method of genetic exchange and recombination in a halobacterial species, was examined. Strains which possessed all naturally-occurring RM system genes in H. volcanii (RM+) and strains without these RM systems ({Delta}RM) were mated together to compare the efficiency of gene transfer between RM-compatible strains and RM-incompatible strains. The results indicated that mating RM-incompatible strains together resulted in a decrease in gene transfer efficiency compared to mating RM-compatible strains together, suggesting that RM systems limit mating in H. volcanii, but do not act as absolute barriers to recombination. Therefore, RM systems are low barriers to recombination in the Halobacteria, with RM-incompatible strains exchanging genetic material at a lower frequency than those with compatible RM systems, similar to other low recombination barriers in the Halobacteria.

evolutionary biology↗

bioRxiv2019

Reconstructing the evolutionary origins of extreme halophilic Archaeal lineages

Interest and controversy surrounding the evolutionary origins of extremely halophilic Archaea has increased in recent years, due to the discovery and characterization of the Nanohaloarchaea and the Methanonatronarchaeia. Initial attempts in explaining the evolutionary placement of the two new lineages in relation to the classical Halobacteria (also referred to as Haloarchaea) resulted in hypotheses that imply the new groups share a common ancestor with the Haloarchaea. However, more recent analyses have led to a shift: the Nanohaloarchaea have been largely accepted as being a member of the DPANN superphylum, outside of the euryarchaeota; while the Methanonatronarchaeia have been placed near the base of the Methanotecta (composed of the class II methanogens, the Halobacteriales, and Archaeoglobales). These opposing hypotheses have far-reaching implications on the concepts of convergent evolution (unrelated groups evolve similar strategies for survival), genome reduction, and gene transfer. In this work, we attempt to resolve these conflicts with phylogenetic and phylogenomic data. We provide a robust taxonomic sampling of Archaeal genomes that spans the Asgardarchaea, TACK Group, euryarchaeota, and the DPANN superphylum. In addition, we assembled draft genomes from seven new representatives of the Nanohaloarchaea from distinct geographic locations. Phylogenies derived from these data imply that the highly conserved ATP synthase catalytic/non-catalytic subunits of Nanohaloarchaea share a sisterhood relationship with the Haloarchaea. We also employ a novel gene family distance clustering strategy which shows this sisterhood relationship is not likely the result of a recent gene transfer. In addition, we present and evaluate data that argue for and against the monophyly of the DPANN superphylum, in particular, the inclusion of the Nanohaloarchaea in DPANN. Significance StatementMany recent analyses have considered large groups of Bacteria and Archaea composed exclusively of environmentally assembled genomes as deep branching taxonomic groups in their respective domains. These groups display characteristics distinct from other members of their domain, which can attract unrelated lineages into those groups. This manuscript evaluates the case of the Nanohaloarchaea, and their inclusion in the DPANN Archaea, through careful analysis of the genes that compose the core of the Nanohaloarchaea. Analyses without inspection of the genes that compose a phylogenomic marker set increases the potential for the inclusion of artifacts and confuses the tree/web of life. Due to horizontal gene transfer and phylogenetic reconstruction artifacts, the placement of divergent archaeal classes into larger groups remains uncertain.

microbiology↗

bioRxiv2019

Interaction of two strongly divergent archaellins stabilizes the structure of the Halorubrum archaellum

The archaellum is a unique motility structure that has only functional similarity to its bacterial counterpart, the flagellum. Archaellar filaments consist of thousands of copies of the protein protomer archaellin. Most euryarchaeal genomes encode multiple homologous archaellins. The role of these multiple archaellin genes remains unclear. Halophilic archaea from the genus Halorubrum possess two archaellin genes, flaB1 and flaB2. Amino acid sequences of the corresponding protein products are extraordinarily diverged (identity of [~] 40%). To clarify roles for each archaellin, we compared archaella from two natural Halorubrum lacusprofundi strains: the DL18 strain, which possesses both archaellin genes, and the type strain ACAM 34 whose genome contains the flaB2 gene only. Both strains synthesize functional archaella; however, the DL18 strain, where both archaellins are present in comparable amounts, is more motile. In addition, we expressed these different Hrr. lacusprofundi archaellins in a Haloferax volcanii strain from which the endogenous archaellin genes were deleted. Three Hfx. volcanii strains expressing Hrr. lacusprofundi archaellins flaB1, flaB2 or flaB1-flaB2 produced archaellum filaments consisting of only one (FlaB1 or FlaB2) or both (FlaB1/B2) archaellins. All three recombinant Hfx. volcanii strains were motile, although there were profound differences in the efficiency of motility. The recombinant filaments resemble the natural filaments of Hrr. lacusprofundi. Electron microscopy showed that FlaB1 FlaB2-archaella look like typical supercoiled filaments, while with the shape of the FlaB1- and FlaB2-archaella is more variable. Both native and recombinant FlaB1 FlaB2-filaments have greater thermal stability and are more resistant to low salinity stress than single-component filaments. This shows that thermal stability of archaellins depends on the presence of both archaellin types, indicating a close interaction between these subunits in the supramolecular structure. Functional helical Hrr. lacusprofundi archaella can be composed of either single archaellin: FlaB2 or FlaB1; however, the two divergent archaellin subunits in combination provide additional stabilization to the archaellum structure and thus adaptation to a wider range of external conditions. A comparative genomic analysis of archaellins suggests that the described combination of divergent archaellins is not restricted to Hrr. lacusprofundi, but is occurring also in organisms from other haloarchaeal genera.

microbiology↗

bioRxiv2019

The Patchy Distribution of Restriction-Modification System Genes and the Conservation of Orphan Methyltransferases in Halobacteria.

Restriction-modification (RM) systems in Bacteria are implicated in multiple biological roles ranging from defense against parasitic genetic elements, to selfish addiction cassettes, and barriers to gene transfer and lineage homogenization. In Bacteria, DNA-methylation without cognate restriction also plays important roles in DNA replication, mismatch repair, protein expression, and in in biasing DNA uptake. Little is known about archaeal RM systems and DNA methylation. To elucidate further understanding for the role of RM systems and DNA methylation in Archaea, we undertook a survey of the presence of RM system genes and related genes, including orphan DNA methylases, in the halophilic archaeal class Halobacteria. Our results reveal that some orphan DNA methyltransferase genes were highly conserved among lineages indicating an important functional constraint, whereas RM systems demonstrated patchy patterns of presence and absence. This irregular distribution is due to frequent horizontal gene transfer and gene loss, a finding suggesting that the evolution and life cycle of RM systems may be best described as that of a selfish genetic element. A putative target motif (CTAG) of one of the orphan methylases was underrepresented in all of the analyzed genomes, whereas another motif (GATC) was overrepresented in most of the haloarchaeal genomes, particularly in those that encoded the cognate orphan methylase.

genomics↗