Computational tools for viral metagenomics and their application in clinical research

AbstractThere are 100 times more virions than eukaryotic cells in a healthy human body. The characterization of human-associated viral communities in a non-pathological state and the detection of viral pathogens in cases of infection are essential for medical care and epidemic surveillance. Viral metagenomics, the sequenced-based analysis of the complete collection of viral genomes directly isolated from an organism or an ecosystem, bypasses the “single-organism-level” point of view of clinical diagnostics and thus the need to isolate and culture the targeted organism. The first part of this review is dedicated to a presentation of past research in viral metagenomics with an emphasis on human-associated viral communities (eukaryotic viruses and bacteriophages). In the second part, we review more precisely the computational challenges posed by the analysis of viral metagenomes, and we illustrate the problem of sequences that do not have homologs in public databases and the possible approaches to characterize them

EXPLORING THE GLOBAL VIROME AND DECIPHERING THE ROLE OF PHAGES IN CYSTIC FIBROSIS

Viruses are the most abundant and diverse life form on Earth. In Chapter 1 of this dissertation, a global census of the number of viral particles showed that 6.03 x 1031 viral particles are distributed across almost every ecosystem. The global census results showed that most viruses are in soils and sediments, two unexplored biomes for viral diversity. Accurate and fast bioinformatics methods to explore viral and bacterial composition in metagenomic datasets are presented in Chapter 2 as “Fragment Recruitment Assembly Purification (FRAP). Phages are viruses that infect bacteria, their role in polymicrobial infections such as Cystic Fibrosis is explored. Cystic Fibrosis is a genetic disease in which the lung phenotype promoted mucus accumulation and microbial colonization. A multi-omics strategy to explore changes in the lung microbial community during acute pulmonary exacerbations is presented in Chapter 3 as the “Cystic Fibrosis Rapid Response: Translating Multi-omics data into Clinically Relevant Information”. In Chapter 4 eight acute exacerbations were studied and a trend of loss of diversity and viral lytic lifestyle was onserved. Two cystic fibrosis patients studied in Chapter 4 were colonized by antibiotic resistant bacteria from the genera Achromobacter. Both patients suffered fatal exacerbations. This motivated the isolation and characterization of lytic phages to be used as antimicrobials against bacterial infections. In Chapter 5 twelve Achromobacter phages are presented and their use as antimicrobials is proposed

Microbial genomic taxonomy

A need for a genomic species definition is emerging from several independent studies worldwide. In this commentary paper, we discuss recent studies on the genomic taxonomy of diverse microbial groups and a unified species definition based on genomics. Accordingly, strains from the same microbial species share >95% Average Amino Acid Identity (AAI) and Average Nucleotide Identity (ANI), >95% identity based on multiple alignment genes, 70% in silico Genome-to-Genome Hybridization similarity (GGDH). Species of the same genus will form monophyletic groups on the basis of 16S rRNA gene sequences, Multilocus Sequence Analysis (MLSA) and supertree analysis. In addition to the established requirements for species descriptions, we propose that new taxa descriptions should also include at least a draft genome sequence of the type strain in order to obtain a clear outlook on the genomic landscape of the novel microbe. The application of the new genomic species definition put forward here will allow researchers to use genome sequences to define simultaneously coherent phenotypic and genomic groups

The Impact of Tiny Organisms: Microbial Communities and Disease States

In the last decade, primarily through the use of sequencing, much has been learned about the trillions of microorganisms that reside in human hosts. These microorganisms play a wide range of roles including helping our immune systems develop, digesting our food, and protecting us from the invasion of pathogenic organisms. My thesis focuses on the characterization of fungal, viral, and bacterial communities in humans, investigating the use of defined microbial communities to cure diseases in animal models, and examining the effects of human microbiome modifications through fecal microbiota transfers. In the first part of this thesis, I use deep sequencing of ribosomal RNA gene tags to characterize the composition of the bacterial, fungal, and archaeal microbiota in pediatric patients with Inflammatory Bowel Disease and healthy controls. Archaeal reads were rare in the pediatric samples, whereas an abundant amount of fungal reads was recovered. Pediatric IBD was found to be associated with reduced diversity in both fungal and bacterial gut microbiota, and specific Candida taxa were increased in abundance in the IBD samples. I, then, describe my use of a variety of experimental and computational methods to study the viral communities of immune-compromised lung transplant recipients. Anelloviruses, circular, single-stranded DNA viruses, were found in all lung samples but were 56 times more abundant in samples from lung transplant recipients as compared to healthy controls or HIV+ subjects. In the third part of this thesis, I describe the use of defined microbial communities in mice, and its ability to reduce the production of ammonia long term and mitigate hepatic encephalopathy. This was shown to be true in both mice on a normal protein diet or a low protein diet. Last, I investigate the transfer of viral communities between humans through FMT and characterize features associated with efficient transmission. A case series where feces from a single donor were used to treat three children with ulcerative colitis was used for the analysis. Ultimately this work showed that multiple viral lineages do transfer between human individuals through fecal microbiota transplants, but in this case series none of the viruses were known to infect human cells. In this thesis, I elucidate numerous roles for the microbiome in pediatric patients with IBD and lung-transplant recipients, show exciting new finding about engineering the microbiota to help with hyperammonia, and finally investigate a possible limitation about using microbial communities as therapeutics. Together this body of work provides insights into the assemblage of tiny organisms that live within us, constantly contributing

From data to science: a multi-Omics analysis of the pathobiome

Humans represent a complex ecosystem colonized not only by our cells but trillions of other microbes such as bacteria, archaea, fungi, and viruses. This microbiome gains increasing interest due to its involvement in human health and disease. While we live in symbiosis with most of these travellers, dysbiosis can lead to the growth of pathogens. Pathobionts are commensal microbes and harmless in healthy individuals until specific circumstances occur. There is increasing interest in studying this pathobiome due to the rise in infections with high mortality rates and stagnant treatment options. Due to the complexity of possible interactions between the host and microbes, studies on microbial interactions are conducted at varying scales. In this thesis, we start to study interactions in small, well-controlled model systems in vitro and then at the community level in vivo. The key technology used to identify, quantify, and characterize microbes and study host- microbe interactions throughout my studies is whole-genome and transcriptome sequencing. While an extensive body of work has focused on understanding the virulence factors of common pathogens, such as Aspergillus and Candida species, very little work has been done on understanding the interplay of those pathogens with the host’s symbionts or other pathogens at the start of my Ph.D. In my Ph.D. project, I used next- generation sequencing, advanced statistical approaches, and machine learning to significantly expanded our knowledge of the life of pathogens from an ecological point of view

Metatranscriptome analysis of the reef-building coral Orbicella faveolata indicates holobiont response to coral disease

White Plague Disease (WPD) is implicated in coral reef decline in the Caribbean and is characterized by microbial community shifts in coral mucus and tissue. Studies thus far have focused on assessing microbial communities or the identification of specific pathogens, yet few have addressed holobiont response across metaorganism compartments in coral disease. Here, we report on the first metatranscriptomic assessment of the coral host, algal symbiont, and microbial compartment in order to survey holobiont structure and function in healthy and diseased samples from Orbicella faveolata collected at reef sites off Puerto Rico. Our data indicate holobiont-wide as well as compartment-specific responses to WPD. Gene expression changes in the diseased coral host involved proteins playing a role in innate immunity, cytoskeletal integrity, cell adhesion, oxidative stress, chemical defense, and retroelements. In contrast, the algal symbiont showed comparatively few expression changes, but of large magnitude, of genes related to stress, photosynthesis, and metal transport. Concordant with the coral host response, the bacterial compartment showed increased abundance of heat shock proteins, genes related to oxidative stress, DNA repair, and potential retroelement activity. Importantly, analysis of the expressed bacterial gene functions establishes the participation of multiple bacterial families in WPD pathogenesis and also suggests a possible involvement of viruses and/or phages in structuring the bacterial assemblage. In this study, we implement an experimental approach to partition the coral holobiont and resolve compartment- and taxa-specific responses in order to understand metaorganism function in coral disease

Viral elements and their potential influence on microbial processes along the permanently stratified Cariaco Basin redoxcline

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Mara, P., Vik, D., Pachiadaki, M. G., Suter, E. A., Poulos, B., Taylor, G. T., Sullivan, M. B., & Edgcomb, V. P. Viral elements and their potential influence on microbial processes along the permanently stratified Cariaco Basin redoxcline. ISME Journal, (2020), doi:10.1038/s41396-020-00739-3.Little is known about viruses in oxygen-deficient water columns (ODWCs). In surface ocean waters, viruses are known to act as gene vectors among susceptible hosts. Some of these genes may have metabolic functions and are thus termed auxiliary metabolic genes (AMGs). AMGs introduced to new hosts by viruses can enhance viral replication and/or potentially affect biogeochemical cycles by modulating key microbial pathways. Here we identify 748 viral populations that cluster into 94 genera along a vertical geochemical gradient in the Cariaco Basin, a permanently stratified and euxinic ocean basin. The viral communities in this ODWC appear to be relatively novel as 80 of these viral genera contained no reference viral sequences, likely due to the isolation and unique features of this system. We identify viral elements that encode AMGs implicated in distinctive processes, such as sulfur cycling, acetate fermentation, signal transduction, [Fe–S] formation, and N-glycosylation. These AMG-encoding viruses include two putative Mu-like viruses, and viral-like regions that may constitute degraded prophages that have been modified by transposable elements. Our results provide an insight into the ecological and biogeochemical impact of viruses oxygen-depleted and euxinic habitats.This work was supported by the National Science Foundation grant OCE-1336082 to VPE, OCE-1335436 to GTT, OCE-1536989, a Moore Foundation Award (#3790) to MBS, and WHOI subaward A101259 to MP. The sequencing conducted by the U.S. Department of Energy Joint Genome Institute is supported by the Office of Science of the U.S. Department of Energy under contract no. DE-AC02-05CH11231

Critical Assessment of Metagenome Interpretation:A benchmark of metagenomics software

International audienceIn metagenome analysis, computational methods for assembly, taxonomic profilingand binning are key components facilitating downstream biological datainterpretation. However, a lack of consensus about benchmarking datasets andevaluation metrics complicates proper performance assessment. The CriticalAssessment of Metagenome Interpretation (CAMI) challenge has engaged the globaldeveloper community to benchmark their programs on datasets of unprecedentedcomplexity and realism. Benchmark metagenomes were generated from newlysequenced ~700 microorganisms and ~600 novel viruses and plasmids, includinggenomes with varying degrees of relatedness to each other and to publicly availableones and representing common experimental setups. Across all datasets, assemblyand genome binning programs performed well for species represented by individualgenomes, while performance was substantially affected by the presence of relatedstrains. Taxonomic profiling and binning programs were proficient at high taxonomicranks, with a notable performance decrease below the family level. Parametersettings substantially impacted performances, underscoring the importance ofprogram reproducibility. While highlighting current challenges in computationalmetagenomics, the CAMI results provide a roadmap for software selection to answerspecific research questions

Diversity of dsDNA marine viral groups during winter in the Arctic Ocean north of Svalbard

Extreme changes in light and cold water temperatures throughout the annual cycle in the Arctic Ocean create a unique habitat that selects for particular microorganisms - including marine viruses. This study investigated diversity of ecologically significant viral groups at two marine sampling stations during the dark period in the Arctic Ocean north of the Svalbard archipelago through pyrosequencing of signature genes. Sequence data for three viral signature genes (g23, phoH, and MCP) were examined within the context of physical and biological environmental parameters to characterize the viral communities within several Arctic Ocean water masses of differing origin. Genotypic fingerprinting information from previous T4- like virus diversity investigations was used to explore phylogenetic relationships between Arctic Ocean g23 genotypes examined in this thesis to a global diversity of T4-like viruses isolated from various environments. Our findings show that marine viral communities exhibit dominant and rare types that vary proportionally in abundance between water masses, and that the available prokaryotic host communities vary similarly. The biogeographic examination showed that many of the dominant Arctic Ocean T4-like genotypes from this study are possibly endemic to the arctic, while others show similarity to globally distributed types, supporting the paradigm that local viral diversity may be high while also being low globally. Additionally, this study compared sequenced datasets of g23 amplicons from the same water samples generated using three widely- implemented sequencing platforms (Roche/454, Illumina, and Ion Torrent) in order to assess comparability of data from newer platforms for viral diversity investigations to pyrosequencing data. The platform comparison revealed that clustering of signature gene sequences into OTUs based on 90% similarity resulted in preservation of broad patterns in between-sample diversity, and also that sequence read data generated using Illumina appear most similar to Roche/454. The author therefore recommends the Illumina platform for continued use of primers for amplification of viral signature genes developed for pyrosequencing.Master i BiologiMAMN-BIOBIO39