The evolution, distribution and diversity of endogenous circoviral elements in vertebrate genomes

Circoviruses (family Circoviridae) are small, non-enveloped viruses that have short, single-stranded DNA genomes. Circovirus sequences are frequently recovered in metagenomic investigations, indicating that these viruses are widespread, yet they remain relatively poorly understood. Endogenous circoviral elements (CVe) are DNA sequences derived from circoviruses that occur in vertebrate genomes. CVe are a useful source of information about the biology and evolution of circoviruses. In this study, we screened 362 vertebrate genome assemblies in silico to generate a catalog of CVe loci. We identified a total of 179 CVe sequences, most of which have not been reported previously. We show that these CVe loci reflect at least 19 distinct germline integration events. We determine the structure of CVe loci, identifying some that show evidence of potential functionalization. We also identify orthologous copies of CVe in snakes, fish, birds, and mammals, allowing us to add new calibrations to the timeline of circovirus evolution. Finally, we observed that some ancient CVe group robustly with contemporary circoviruses in phylogenies, with all sequences within these groups being derived from the same host class or order, implying a hitherto underappreciated stability in circovirus-host relationships. The openly available dataset constructed in this investigation provides new insights into circovirus evolution, and can be used to facilitate further studies of circoviruses and CVe

Insights into circovirus host range from the genomic fossil record

A diverse range of DNA sequences derived from circoviruses (family Circoviridae) have been identified in samples obtained from humans and domestic animals, often in association with pathological conditions. In the majority of cases, however, little is known about the natural biology of the viruses from which these sequences are derived. Endogenous circoviral elements (CVe) are DNA sequences derived from circoviruses that occur in animal genomes and provide a useful source of information about circovirus-host relationships. In this study we screened genome assemblies of 675 animal species and identified numerous circovirus-related sequences, including the first examples of CVe derived from cycloviruses. We confirmed the presence of these CVe in the germline of the elongate twig ant (Pseudomyrmex gracilis), thereby establishing that cycloviruses infect insects. We examined the evolutionary relationships between CVe and contemporary circoviruses, showing that CVe from ants and mites group relatively closely with cycloviruses in phylogenies. Furthermore, the relatively random interspersal of CVe from insect genomes with cyclovirus sequences recovered from vertebrate samples, suggested that contamination might be an important consideration in studies reporting these viruses. Our study demonstrates how endogenous viral sequences can inform metagenomics-based virus discovery. In addition, it raises doubts about the role of cycloviruses as pathogens of humans and other vertebrates

Signatures of adaptation at key insecticide resistance loci in Anopheles gambiae in Southern Ghana revealed by reduced-coverage WGS

Resistance to insecticides and adaptation to a diverse range of environments present challenges to Anopheles gambiae s.l. mosquito control efforts in sub-Saharan Africa. Whole-genome-sequencing is often employed for identifying the genomic basis underlying adaptation in Anopheles, but remains expensive for large-scale surveys. Reduced coverage whole-genome-sequencing can identify regions of the genome involved in adaptation at a lower cost, but is currently untested in Anopheles mosquitoes. Here, we use reduced coverage WGS to investigate population genetic structure and identify signatures of local adaptation in Anopheles mosquitoes across southern Ghana. In contrast to previous analyses, we find no structuring by ecoregion, with Anopheles coluzzii and Anopheles gambiae populations largely displaying the hallmarks of large, unstructured populations. However, we find signatures of selection at insecticide resistance loci that appear ubiquitous across ecoregions in An. coluzzii, and strongest in forest ecoregions in An. gambiae. Our study highlights resistance candidate genes in this region, and validates reduced coverage WGS, potentially to very low coverage levels, for population genomics and exploratory surveys for adaptation in Anopheles taxa

Target-enrichment sequencing yields valuable genomic data for challenging-to-culture bacteria of public health importance

Genomic data contribute invaluable information to the epidemiological investigation of pathogens of public health importance. However, whole-genome sequencing (WGS) of bacteria typically relies on culture, which represents a major hurdle for generating such data for a wide range of species for which culture is challenging. In this study, we assessed the use of culture-free target-enrichment sequencing as a method for generating genomic data for two bacterial species: (1) Bacillus anthracis, which causes anthrax in both people and animals and whose culture requires high-level containment facilities; and (2) Mycoplasma amphoriforme, a fastidious emerging human respiratory pathogen. We obtained high-quality genomic data for both species directly from clinical samples, with sufficient coverage (>15×) for confident variant calling over at least 80% of the baited genomes for over two thirds of the samples tested. Higher qPCR cycle threshold (Ct) values (indicative of lower pathogen concentrations in the samples), pooling libraries prior to capture, and lower captured library concentration were all statistically associated with lower capture efficiency. The Ct value had the highest predictive value, explaining 52 % of the variation in capture efficiency. Samples with Ct values ≤30 were over six times more likely to achieve the threshold coverage than those with a Ct > 30. We conclude that target-enrichment sequencing provides a valuable alternative to standard WGS following bacterial culture and creates opportunities for an improved understanding of the epidemiology and evolution of many clinically important pathogens for which culture is challenging