Metagenome-assembled genomes and gene catalog from the chicken gut microbiome aid in deciphering antibiotic resistomes

Gut microbial reference genomes and gene catalogs are necessary for understanding the chicken gut microbiome. Here, we assembled 12,339 microbial genomes and constructed a gene catalog consisting of ~16.6 million genes by integrating 799 public chicken gut microbiome samples from ten countries. We found that 893 and 38 metagenome-assembled genomes (MAGs) in our dataset were putative novel species and genera, respectively. In the chicken gut, Lactobacillus aviarius and Lactobacillus crispatus were the most common lactic acid bacteria, and glycoside hydrolases were the most abundant carbohydrate-active enzymes (CAZymes). Antibiotic resistome profiling results indicated that Chinese chicken samples harbored a higher relative abundance but less diversity of antimicrobial resistance genes (ARGs) than European samples. We also proposed the effects of geography and host species on the gut resistome. Our study provides the largest integrated metagenomic dataset from the chicken gut to date and demonstrates its value in exploring chicken gut microbial genes.

Eukaryotic genomes from a global metagenomic dataset illuminate trophic modes and biogeography of ocean plankton

Molecular and genomic approaches that target mixed microbial communities (e.g., metagenomics or metatranscriptomics) provide insight into the ecological roles, evolutionary histories, and physiological capabilities of the microorganisms and the processes in the environment. Computational tools that harness large-scale sequence surveys have become a valuable resource for characterizing the genetic make-up of the bacterial and archaeal component of the marine microbiome. Yet, fewer studies have focused on the unicellular eukaryotic fraction of the community. Here, we developed the EukHeist automated computational pipeline, to retrieve eukaryotic and prokaryotic metagenome assembled genomes (MAGs). We applied EukHeist to the eukaryote-dominated large-size fraction data (0.8-2000 μm) from the Tara Oceans survey to recover both eukaryotic and prokaryotic MAGs, which we refer to as TOPAZ (Tara Oceans Particle-Associated MAGs). The TOPAZ MAGs consisted of more than 900 eukaryotic MAGs representing environmentally-relevant microbial and multicellular eukaryotes in addition to over 4,000 bacterial and archaeal MAGs. The bacterial and archaeal TOPAZ MAGs retrieved with EukHeist complement previous efforts by expanding the existing phylogenetic diversity through the increase in coverage of many likely particle- and host-associated taxa. We also demonstrate how the novel eukaryotic genomic content recovered from this study might be used to infer functional traits, such as trophic mode. By coupling MAGs and metatranscriptomic data, we explored ecologically-significant protistan groups, such as the Stramenopiles. A global survey of both eukaryotic and prokaryotic MAGs enabled the identification of ecological cohorts, driven by specific environmental factors, and putative host-microbe associations. Accessible and scalable computational tools, such as EukHeist, are likely to accelerate the identification of meaningful genetic signatures from large datasets, ultimately expanding the eukaryotic tree of life.

A metagenomic view of novel microbial and metabolic diversity found within the deep terrestrial biosphere

The deep terrestrial subsurface is a large and diverse microbial habitat and a vast repository of biomass. However, in relation to its size and physical heterogeneity we have limited understanding of taxonomic and metabolic diversity in this realm. Here we present a detailed metagenomic analysis of samples from the Deep Mine Microbial Observatory (DeMMO) spanning depths from the surface to 1.5 km deep in the crust. From these eight geochemically and spatially distinct fluid samples we reconstructed ~600 metagenome assembled genomes (MAGs), representing 50 distinct phyla and including 18 candidate phyla. These novel clades include many members of the Patescibacteria superphylum and two new MAGs from candidate phylum OLB16, a phylum originally identified in DeMMO fluids and for which only one other MAG is currently available. We find that microbes spanning this expansive phylogenetic diversity and physical space are often capable of numerous dissimilatory energy metabolisms and are poised to take advantage of nutrients as they become available in relatively isolated fracture fluids. This metagenomic dataset is contextualized within a four-year geochemical and 16S rRNA time series, adding another invaluable piece to our knowledge of deep subsurface microbial ecology.

Truncated denitrifiers dominate the denitrification pathway in tundra soil metagenomes

In contrast to earlier assumptions, there is now mounting evidence for the role of tundra soils as important sources of the greenhouse gas nitrous oxide (N2O). However, the microorganisms involved in the cycling of N2O in these soils remain largely uncharacterized. In this study, we manually binned and curated 541 metagenome-assembled genomes (MAGs) from tundra soils in northern Finland. We then searched for MAGs encoding enzymes involved in denitrification, the main biotic process driving N2O emissions. Denitrifying communities were dominated by poorly characterized taxa with truncated denitrification pathways, i.e. lacking one or more denitrification genes. Among these, MAGs with the metabolic potential to produce N2O comprised the most diverse functional group. Re-analysis of a previously published metagenomic dataset from soils in northern Sweden supported these results, suggesting that truncated denitrifiers are dominant throughout the tundra biome.

The conservation of a core virome in Aedes mosquitoes across different developmental stages and continents

Mosquitoes belonging to the genus Aedes can efficiently transmit many pathogenic arboviruses, placing a great burden on public health worldwide. In addition, they also carry a number of insect specific viruses (ISVs), and it was recently suggested that some of these ISVs might form a stable species-specific “core virome” in mosquito populations. However, little is known about such a core virome in laboratory colonies and if it is present across different developmental stages. In this study, we compared the viromes in eggs, larvae, pupae and adults of Aedes albopictus mosquitoes collected from the field as well as from a lab colony. The virome in lab-derived Ae. albopictus is very stable across all stages, consistent with a vertical transmission route of these viruses, forming a “vertically transmitted core virome”. The different stages of field collected Ae. albopictus mosquitoes also contains this stable vertically transmitted core virome as well as another set of viruses shared by mosquitoes across different stages, which might be an “environment derived core virome”. Both these vertically and environmentally transmitted core viromes in Ae. albopictus deserve more attention with respect to their effects on vector competence for important medically relevant arboviruses. To further study this core set of ISVs, we screened 46 publically available SRA viral metagenomic dataset of mosquitoes belonging to the genus Aedes. Some of the identified core ISVs are identified in the majority of SRAs. In addition, a novel virus, Aedes phasmavirus, is found to be distantly related to Yongsan bunyavirus 1, and the genomes of the core virus Phasi Charoen-like phasivirus is highly prevalent in the majority of the tested samples, with nucleotide identities ranging from 94% to 99%. Finally, Guadeloupe mosquito virus, and some related viruses formed three separated phylogenetic clades. How these core ISVs influence the biology of mosquito host, arboviruses infection and evolution deserve to be further explored.

Evidence of recombination in coronaviruses implicating pangolin origins of nCoV-2019

SUMMARYA novel coronavirus (nCoV-2019) was the cause of an outbreak of respiratory illness detected in Wuhan, Hubei Province, China in December of 2019. Genomic analyses of nCoV-2019 determined a 96% resemblance with a coronavirus isolated from a bat in 2013 (RaTG13); however, the receptor binding motif (RBM) of these two genomes share low sequence similarity. This divergence suggests a possible alternative source for the RBM coding sequence in nCoV-2019. We identified high sequence similarity in the RBM between nCoV-2019 and a coronavirus genome reconstructed from a viral metagenomic dataset from pangolins possibly indicating a more complex origin for nCoV-2019.

InStrain enables population genomic analysis from metagenomic data and rigorous detection of identical microbial strains

Coexisting microbial cells of the same species often exhibit genetic differences that can affect phenotypes ranging from nutrient preference to pathogenicity. Here we present inStrain, a program that utilizes metagenomic paired reads to profile intra-population genetic diversity (microdiversity) across whole genomes and compare populations in a microdiversity-aware manner, dramatically increasing genomic comparison accuracy when benchmarked against existing methods. We use inStrain to profile >1,000 fecal metagenomes from newborn premature infants and find that siblings share significantly more strains than unrelated infants, although identical twins share no more strains than fraternal siblings. Infants born via cesarean section harbored Klebsiella with significantly higher nucleotide diversity than infants delivered vaginally, potentially reflecting acquisition from hospital versus maternal microbiomes. Genomic loci showing diversity within an infant included variants found in other infants, possibly reflecting inoculation from diverse hospital-associated sources. InStrain can be applied to any metagenomic dataset for microdiversity analysis and rigorous strain comparison.