Use of a sample-to-result shotgun metagenomics platform for the detection and quantification of viral pathogens in paediatric immunocompromised patients.

Background: Infections by several DNA viruses can severely impact outcomes in paediatric immunocompromised patients. Current testing, which is generally limited to singleplex qPCR assays, can miss both common and rarer viruses if they are not targeted. Objectives: To evaluate the performance of the Galileo Viral Panel (Galileo), a sample-to-result shotgun metagenomics platform for the detection and quantification of 12 DNA viruses, compared to standard of care qPCR assays. Study design: A clinical performance evaluation was carried out using 43 prospectively collected EDTA plasma samples positive for one or more DNA viruses. Agreement between assays was assessed by overall, positive, and negative percent agreement, as well as quantitative agreement by linear regression and Bland-Altman analysis. Results: Overall positive percent agreement was 84% (95% CI: 76%-90%), and negative percent agreement was 95% (95% CI: 92%-97%). There was a high correlation between Galileo and qPCR for ADV, CMV, EBV, and VZV (R2  = 0.91) and a mean difference by Bland Altman of -0.43 log10 IU or cp/ml (95% limits of agreement, -1.37 to 0.51). In addition, there was a high correlation between Galileo Signal Score and qPCR for TTV (R2  = 0.85). Conclusion: We observed high qualitative and quantitative agreement between qPCR and Galileo. Galileo identified additional viruses that were not tested with routine qPCR and could impact clinical outcomes.

Metagenomic Next-Generation Sequencing for Identification and Quantitation of Transplant-Related DNA Viruses.

Infections with DNA viruses are frequent causes of morbidity and mortality in transplant recipients. This study describes the analytical and clinical performance characteristics of the Arc Bio Galileo Pathogen Solution, an all-inclusive metagenomic next-generation sequencing (mNGS) reagent and bioinformatics pipeline that allows the simultaneous quantitation of 10 transplant-related double-stranded DNA (dsDNA) viruses (adenovirus [ADV], BK virus [BKV], cytomegalovirus [CMV], Epstein-Barr virus [EBV], human herpesvirus 6A [HHV-6A], HHV-6B, herpes simplex virus 1 [HSV-1], HSV-2, JC virus [JCV], and varicella-zoster virus [VZV]). The mNGS 95% limit of detection ranged from 14 copies/ml (HHV-6) to 191 copies/ml (BKV), and the lower limit of quantitation ranged from 442 international units (IU)/ml (EBV) to 661 copies/ml (VZV). An evaluation of 50 residual plasma samples with at least one DNA virus detected in prior clinical testing showed a total percent agreement of mNGS and quantitative PCR (qPCR) of 89.2% (306/343), with a κ statistic of 0.725. The positive percent agreement was 84.9% (73/86), and the negative percent agreement was 90.7% (233/257). Furthermore, mNGS detected seven subsequently confirmed coinfections that were not initially requested by qPCR. Passing-Bablok regression revealed a regression line of y = 0.953x + 0.075 (95% confidence interval [CI] of the slope, 0.883 to 1.011; intercept, -0.100 to 0.299), and Bland-Altman analysis (mNGS - qPCR) showed a slight positive bias (0.28 log10 concentration; 95% limits of agreement, -0.62 to 1.18). In conclusion, the mNGS-based Galileo pipeline demonstrates analytical and clinical performance comparable to that of qPCR for transplant-related DNA viruses.

Genomic insights into the origin and diversification of late maritime hunter-gatherers from the Chilean Patagonia.

Patagonia was the last region of the Americas reached by humans who entered the continent from Siberia ∼15,000-20,000 y ago. Despite recent genomic approaches to reconstruct the continental evolutionary history, regional characterization of ancient and modern genomes remains understudied. Exploring the genomic diversity within Patagonia is not just a valuable strategy to gain a better understanding of the history and diversification of human populations in the southernmost tip of the Americas, but it would also improve the representation of Native American diversity in global databases of human variation. Here, we present genome data from four modern populations from Central Southern Chile and Patagonia (n = 61) and four ancient maritime individuals from Patagonia (∼1,000 y old). Both the modern and ancient individuals studied in this work have a greater genetic affinity with other modern Native Americans than to any non-American population, showing within South America a clear structure between major geographical regions. Native Patagonian Kawéskar and Yámana showed the highest genetic affinity with the ancient individuals, indicating genetic continuity in the region during the past 1,000 y before present, together with an important agreement between the ethnic affiliation and historical distribution of both groups. Lastly, the ancient maritime individuals were genetically equidistant to a ∼200-y-old terrestrial hunter-gatherer from Tierra del Fuego, which supports a model with an initial separation of a common ancestral group to both maritime populations from a terrestrial population, with a later diversification of the maritime groups.

Genome-wide ancestry of 17th-century enslaved Africans from the Caribbean.

Between 1500 and 1850, more than 12 million enslaved Africans were transported to the New World. The vast majority were shipped from West and West-Central Africa, but their precise origins are largely unknown. We used genome-wide ancient DNA analyses to investigate the genetic origins of three enslaved Africans whose remains were recovered on the Caribbean island of Saint Martin. We trace their origins to distinct subcontinental source populations within Africa, including Bantu-speaking groups from northern Cameroon and non-Bantu speakers living in present-day Nigeria and Ghana. To our knowledge, these findings provide the first direct evidence for the ethnic origins of enslaved Africans, at a time for which historical records are scarce, and demonstrate that genomic data provide another type of record that can shed new light on long-standing historical questions.

Population genomic analysis of ancient and modern genomes yields new insights into the genetic ancestry of the Tyrolean Iceman and the genetic structure of Europe.

Genome sequencing of the 5,300-year-old mummy of the Tyrolean Iceman, found in 1991 on a glacier near the border of Italy and Austria, has yielded new insights into his origin and relationship to modern European populations. A key finding of that study was an apparent recent common ancestry with individuals from Sardinia, based largely on the Y chromosome haplogroup and common autosomal SNP variation. Here, we compiled and analyzed genomic datasets from both modern and ancient Europeans, including genome sequence data from over 400 Sardinians and two ancient Thracians from Bulgaria, to investigate this result in greater detail and determine its implications for the genetic structure of Neolithic Europe. Using whole-genome sequencing data, we confirm that the Iceman is, indeed, most closely related to Sardinians. Furthermore, we show that this relationship extends to other individuals from cultural contexts associated with the spread of agriculture during the Neolithic transition, in contrast to individuals from a hunter-gatherer context. We hypothesize that this genetic affinity of ancient samples from different parts of Europe with Sardinians represents a common genetic component that was geographically widespread across Europe during the Neolithic, likely related to migrations and population expansions associated with the spread of agriculture.

Exome capture from saliva produces high quality genomic and metagenomic data.

BACKGROUND: Targeted capture of genomic regions reduces sequencing cost while generating higher coverage by allowing biomedical researchers to focus on specific loci of interest, such as exons. Targeted capture also has the potential to facilitate the generation of genomic data from DNA collected via saliva or buccal cells. DNA samples derived from these cell types tend to have a lower human DNA yield, may be degraded from age and/or have contamination from bacteria or other ambient oral microbiota. However, thousands of samples have been previously collected from these cell types, and saliva collection has the advantage that it is a non-invasive and appropriate for a wide variety of research. RESULTS: We demonstrate successful enrichment and sequencing of 15 South African KhoeSan exomes and 2 full genomes with samples initially derived from saliva. The expanded exome dataset enables us to characterize genetic diversity free from ascertainment bias for multiple KhoeSan populations, including new exome data from six HGDP Namibian San, revealing substantial population structure across the Kalahari Desert region. Additionally, we discover and independently verify thirty-one previously unknown KIR alleles using methods we developed to accurately map and call the highly polymorphic HLA and KIR loci from exome capture data. Finally, we show that exome capture of saliva-derived DNA yields sufficient non-human sequences to characterize oral microbial communities, including detection of bacteria linked to oral disease (e.g. Prevotella melaninogenica). For comparison, two samples were sequenced using standard full genome library preparation without exome capture and we found no systematic bias of metagenomic information between exome-captured and non-captured data. CONCLUSIONS: DNA from human saliva samples, collected and extracted using standard procedures, can be used to successfully sequence high quality human exomes, and metagenomic data can be derived from non-human reads. We find that individuals from the Kalahari carry a higher oral pathogenic microbial load than samples surveyed in the Human Microbiome Project. Additionally, rare variants present in the exomes suggest strong population structure across different KhoeSan populations.

Pulling out the 1%: whole-genome capture for the targeted enrichment of ancient DNA sequencing libraries.

Most ancient specimens contain very low levels of endogenous DNA, precluding the shotgun sequencing of many interesting samples because of cost. Ancient DNA (aDNA) libraries often contain <1% endogenous DNA, with the majority of sequencing capacity taken up by environmental DNA. Here we present a capture-based method for enriching the endogenous component of aDNA sequencing libraries. By using biotinylated RNA baits transcribed from genomic DNA libraries, we are able to capture DNA fragments from across the human genome. We demonstrate this method on libraries created from four Iron Age and Bronze Age human teeth from Bulgaria, as well as bone samples from seven Peruvian mummies and a Bronze Age hair sample from Denmark. Prior to capture, shotgun sequencing of these libraries yielded an average of 1.2% of reads mapping to the human genome (including duplicates). After capture, this fraction increased substantially, with up to 59% of reads mapped to human and enrichment ranging from 6- to 159-fold. Furthermore, we maintained coverage of the majority of regions sequenced in the precapture library. Intersection with the 1000 Genomes Project reference panel yielded an average of 50,723 SNPs (range 3,062-147,243) for the postcapture libraries sequenced with 1 million reads, compared with 13,280 SNPs (range 217-73,266) for the precapture libraries, increasing resolution in population genetic analyses. Our whole-genome capture approach makes it less costly to sequence aDNA from specimens containing very low levels of endogenous DNA, enabling the analysis of larger numbers of samples.

Nuclear inheritance and genetic exchange without meiosis in the binucleate parasite Giardia intestinalis.

The protozoan parasite Giardia intestinalis (also known as Giardia lamblia) is a major waterborne pathogen. During its life cycle, Giardia alternates between the actively growing trophozoite, which has two diploid nuclei with low levels of allelic heterozygosity, and the infectious cyst, which has four nuclei and a tough outer wall. Although the formation of the cyst wall has been studied extensively, we still lack basic knowledge about many fundamental aspects of the cyst, including the sources of the four nuclei and their distribution during the transformation from cyst into trophozoite. In this study, we tracked the identities of the nuclei in the trophozoite and cyst using integrated nuclear markers and immunofluorescence staining. We demonstrate that the cyst is formed from a single trophozoite by a mitotic division without cytokinesis and not by the fusion of two trophozoites. During excystation, the cell completes cytokinesis to form two daughter trophozoites. The non-identical nuclear pairs derived from the parent trophozoite remain associated in the cyst and are distributed to daughter cells during excystation as pairs. Thus, nuclear sorting (such that each daughter cell receives a pair of identical nuclei) does not appear to be a mechanism by which Giardia reduces heterozygosity between its nuclei. Rather, we show that the cyst nuclei exchange chromosomal genetic material, perhaps as a way to reduce heterozygosity in the absence of meiosis and sex, which have not been described in Giardia. These results shed light on fundamental aspects of the Giardia life cycle and have implications for our understanding of the population genetics and cell biology of this binucleate parasite.

The genome of Naegleria gruberi illuminates early eukaryotic versatility.

Genome sequences of diverse free-living protists are essential for understanding eukaryotic evolution and molecular and cell biology. The free-living amoeboflagellate Naegleria gruberi belongs to a varied and ubiquitous protist clade (Heterolobosea) that diverged from other eukaryotic lineages over a billion years ago. Analysis of the 15,727 protein-coding genes encoded by Naegleria's 41 Mb nuclear genome indicates a capacity for both aerobic respiration and anaerobic metabolism with concomitant hydrogen production, with fundamental implications for the evolution of organelle metabolism. The Naegleria genome facilitates substantially broader phylogenomic comparisons of free-living eukaryotes than previously possible, allowing us to identify thousands of genes likely present in the pan-eukaryotic ancestor, with 40% likely eukaryotic inventions. Moreover, we construct a comprehensive catalog of amoeboid-motility genes. The Naegleria genome, analyzed in the context of other protists, reveals a remarkably complex ancestral eukaryote with a rich repertoire of cytoskeletal, sexual, signaling, and metabolic modules.

Using morpholinos for gene knockdown in Giardia intestinalis.

We used translation-blocking morpholinos to reduce protein levels in Giardia intestinalis. Twenty-four hours after electroporation with morpholinos targeting either green fluorescent protein or kinesin-2b, levels of these proteins were reduced by 60%. An epitope-tagged transgene can also be used as a reporter for morpholino efficacy with targets lacking specific antibodies.

The Trichoplax genome and the nature of placozoans.

As arguably the simplest free-living animals, placozoans may represent a primitive metazoan form, yet their biology is poorly understood. Here we report the sequencing and analysis of the approximately 98 million base pair nuclear genome of the placozoan Trichoplax adhaerens. Whole-genome phylogenetic analysis suggests that placozoans belong to a 'eumetazoan' clade that includes cnidarians and bilaterians, with sponges as the earliest diverging animals. The compact genome shows conserved gene content, gene structure and synteny in relation to the human and other complex eumetazoan genomes. Despite the apparent cellular and organismal simplicity of Trichoplax, its genome encodes a rich array of transcription factor and signalling pathway genes that are typically associated with diverse cell types and developmental processes in eumetazoans, motivating further searches for cryptic cellular complexity and/or as yet unobserved life history stages.

Evidence for karyogamy and exchange of genetic material in the binucleate intestinal parasite Giardia intestinalis.

The diplomonad parasite Giardia intestinalis contains two functionally equivalent nuclei that are inherited independently during mitosis. Although presumed to be asexual, Giardia has low levels of allelic heterozygosity, indicating that the two nuclear genomes may exchange genetic material. Fluorescence in situ hybridization performed with probes to an episomal plasmid suggests that plasmids are transferred between nuclei in the cyst, and transmission electron micrographs demonstrate fusion between cyst nuclei. Green fluorescent protein fusions of giardial homologs of meiosis-specific genes localized to the nuclei of cysts, but not the vegetative trophozoite. These data suggest that the fusion of nuclei, or karyogamy, and subsequently somatic homologous recombination facilitated by the meiosis gene homologs, occur in the giardial cyst.