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        <title>eggNOG-mapper v2: Functional Annotation, Orthology Assignments, and Domain Prediction at the Metagenomic Scale</title>
        <author>Carlos P Cantalapiedra</author>
        <author>Ana Hernández-Plaza</author>
        <author>Ivica Letunic</author>
        <author>Peer Bork</author>
        <author>Jaime Huerta-Cepas</author>
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          <title>eggNOG-mapper v2: Functional Annotation, Orthology Assignments, and Domain Prediction at the Metagenomic Scale</title>
          <date>2021</date>
          <publisher>Molecular Biology and Evolution</publisher>
          <idno type="DOI">10.1093/molbev/msab293</idno>
          
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      <span xml:id="t0" from="#a1" to="#a2" type="object_of_study" ana="#object_of_study" resp="#paper">the coverage, performance, workflow, and metagenomic-scale capabilities of eggNOG-mapper v2</span>
      <span xml:id="t1" from="#a3" to="#a4" type="research_question" ana="#research_question" resp="#paper">how to make orthology-based automated functional annotation more scalable, versatile, and accurate for large genomic and metagenomic data sets</span>
      <span xml:id="t2" from="#a1" to="#a2" type="contribution" ana="#contribution" resp="#paper">eggNOG-mapper v2, with eggNOG v5 coverage, faster mapping, contig-level gene prediction, pairwise orthology, domain prediction, and GFF decoration</span>
      <span xml:id="t3" from="#a1" to="#a2" type="claim_type" ana="#claim_type" resp="#paper">method</span>
      <span xml:id="t4" from="#a3" to="#a4" type="phenomenon" ana="#phenomenon" resp="#paper">large-scale transfer of gene functions and protein-domain annotations through taxonomically refined orthology</span>
      <span xml:id="t5" from="#a11" to="#a12" type="method" ana="#method" resp="#paper">system-or-tool-building<term>system-or-tool-building</term></span>
      <span xml:id="t6" from="#a3" to="#a4" type="mechanisms" ana="#mechanisms[0]" resp="#tagger" cert="0.95">Precomputed OG phylogenies refine orthology assignments and limit transfer from putative in-paralogs.<term>phylogeny-refined orthology transfer</term></span>
      <span xml:id="t7" from="#a5" to="#a6" type="mechanisms" ana="#mechanisms[1]" resp="#tagger" cert="0.95">Prodigal prediction is followed by sequence search, taxonomically scoped orthology inference, and annotation/domain transfer.<term>four-stage workflow</term></span>
      <span xml:id="t8" from="#a7" to="#a8" type="mechanisms" ana="#mechanisms[2]" resp="#tagger" cert="0.95">Synchronization with eggNOG v5 expands organism and orthologous-group coverage and phylogenetic resolution.<term>database expansion</term></span>
      <span xml:id="t9" from="#a9" to="#a10" type="mechanisms" ana="#mechanisms[3]" resp="#tagger" cert="0.95">A memory-based mode reduces the impact of slow disk I/O on annotation rate.<term>memory-resident querying</term></span>
      <span xml:id="t10" from="#a13" to="#a14" type="mechanisms" ana="#mechanisms[4]" resp="#tagger" cert="0.95">Prodigal turns prokaryotic assembled contigs into protein sequences for annotation.<term>Prodigal ORF prediction</term></span>
      <span xml:id="t11" from="#a15" to="#a16" type="mechanisms" ana="#mechanisms[5]" resp="#tagger" cert="0.95">Diamond&#x27;s iterate mode applies successive sensitivity levels to improve search efficiency.<term>iterative Diamond search</term></span>
      <span xml:id="t12" from="#a17" to="#a18" type="mechanisms" ana="#mechanisms[6]" resp="#tagger" cert="0.95">Diamond or MMseqs2 maps nucleotide sequencing reads without requiring prior assembly.<term>blastx-like mapping</term></span>
      <span xml:id="t13" from="#a19" to="#a20" type="mechanisms" ana="#mechanisms[7]" resp="#tagger" cert="0.95">Automatic or lineage-specific scopes limit the orthologs permitted to transfer annotations.<term>taxonomic-scope filtering</term></span>
      <span xml:id="t14" from="#a25" to="#a26" type="mechanisms" ana="#mechanisms[8]" resp="#tagger" cert="0.95">PFAM annotations are transferred from inferred orthologs at little computational cost.<term>ortholog-domain transfer</term></span>
      <span xml:id="t15" from="#a25" to="#a26" type="mechanisms" ana="#mechanisms[9]" resp="#tagger" cert="0.95">HMMER3 realignment refines transferred domains and applies GA thresholds and clan disambiguation.<term>PFAM realignment refinement</term></span>
      <span xml:id="t16" from="#a1" to="#a2" type="limitations" ana="#limitations[0]" resp="#tagger" cert="0.95">Automated gene-function annotation remains challenging at large genomic and metagenomic scales.</span>
      <span xml:id="t17" from="#a3" to="#a4" type="limitations" ana="#limitations[1]" resp="#tagger" cert="0.95">Orthology delineation is computationally and algorithmically demanding, so many tools rely on homology instead.</span>
      <span xml:id="t18" from="#a13" to="#a14" type="limitations" ana="#limitations[2]" resp="#tagger" cert="0.95">ORF detection is available only for prokaryotic assemblies.</span>
      <span xml:id="t19" from="#a17" to="#a18" type="limitations" ana="#limitations[3]" resp="#tagger" cert="0.95">Direct nucleotide translation assumes coding sequences begin in an open reading frame.</span>
      <span xml:id="t20" from="#a17" to="#a18" type="limitations" ana="#limitations[4]" resp="#tagger" cert="0.95">HMMER3 is substantially slower than Diamond and MMseqs2 and requires large local databases.</span>
      <span xml:id="t21" from="#a21" to="#a22" type="limitations" ana="#limitations[5]" resp="#tagger" cert="0.95">Pairwise orthology reports are a first-pass result and are not intended to replace more precise methods.</span>
      <span xml:id="t22" from="#a25" to="#a26" type="limitations" ana="#limitations[6]" resp="#tagger" cert="0.95">Direct ortholog transfer of PFAM domains has residual false-positive and false-negative predictions.</span>
      <span xml:id="t23" from="#a29" to="#a30" type="limitations" ana="#limitations[7]" resp="#tagger" cert="0.95">Direct blastx-like annotation of reads is available but is not recommended in terms of accuracy.</span>
      <span xml:id="t24" from="#a7" to="#a8" type="controls" ana="#controls[0]" resp="#tagger" cert="0.95">reannotation of 1.75 million randomly subsampled human-gut proteins<note>eliminates: coverage gains caused only by a small hand-selected test set · outcome: held</note></span>
      <span xml:id="t25" from="#a7" to="#a8" type="controls" ana="#controls[1]" resp="#tagger" cert="0.95">Wilcoxon comparison of query alignment scores<note>eliminates: treating apparent phylogenetic-resolution improvement as an untested visual difference · outcome: held</note></span>
      <span xml:id="t26" from="#a11" to="#a12" type="controls" ana="#controls[2]" resp="#tagger" cert="0.95">full de novo PFAM realignment used as the reference<note>eliminates: evaluating transferred-domain accuracy without an independent computational reference · outcome: held</note></span>
      <span xml:id="t27" from="#a11" to="#a12" type="controls" ana="#controls[3]" resp="#tagger" cert="0.95">random proteome, genome, and protein sets with stated CPU and RAM allocations<note>eliminates: unreported scale and compute conditions in runtime comparisons</note></span>
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      <span xml:id="t66" from="#a9" to="#a10" type="concepts" ana="#concepts[38]" resp="#paper" cert="0.95">Prokka<term>Prokka</term></span>
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      <span xml:id="t68" from="#a13" to="#a14" type="concepts" ana="#concepts[40]" resp="#paper" cert="0.95">protein sequences<term>protein sequences</term></span>
      <span xml:id="t69" from="#a13" to="#a14" type="concepts" ana="#concepts[41]" resp="#paper" cert="0.95">custom translation tables<term>custom translation tables</term></span>
      <span xml:id="t70" from="#a15" to="#a16" type="concepts" ana="#concepts[42]" resp="#paper" cert="0.95">sequence-mapping step<term>sequence-mapping step</term></span>
      <span xml:id="t71" from="#a15" to="#a16" type="concepts" ana="#concepts[43]" resp="#paper" cert="0.95">Diamond mode<term>Diamond mode</term></span>
      <span xml:id="t72" from="#a15" to="#a16" type="concepts" ana="#concepts[44]" resp="#paper" cert="0.95">MMseqs2 mode<term>MMseqs2 mode</term></span>
      <span xml:id="t73" from="#a17" to="#a18" type="concepts" ana="#concepts[45]" resp="#paper" cert="0.95">direct translation<term>direct translation</term></span>
      <span xml:id="t74" from="#a17" to="#a18" type="concepts" ana="#concepts[46]" resp="#paper" cert="0.95">blastx-like mode<term>blastx-like mode</term></span>
      <span xml:id="t75" from="#a17" to="#a18" type="concepts" ana="#concepts[47]" resp="#paper" cert="0.95">sequencing reads<term>sequencing reads</term></span>
      <span xml:id="t76" from="#a17" to="#a18" type="concepts" ana="#concepts[48]" resp="#paper" cert="0.95">frameshift option<term>frameshift option</term></span>
      <span xml:id="t77" from="#a17" to="#a18" type="concepts" ana="#concepts[49]" resp="#paper" cert="0.95">HMM-based searches<term>HMM-based searches</term></span>
      <span xml:id="t78" from="#a17" to="#a18" type="concepts" ana="#concepts[50]" resp="#paper" cert="0.95">distant homology relationships<term>distant homology relationships</term></span>
      <span xml:id="t79" from="#a19" to="#a20" type="concepts" ana="#concepts[51]" resp="#paper" cert="0.95">custom annotation databases<term>custom annotation databases</term></span>
      <span xml:id="t80" from="#a19" to="#a20" type="concepts" ana="#concepts[52]" resp="#paper" cert="0.95">specific taxonomic groups<term>specific taxonomic groups</term></span>
      <span xml:id="t81" from="#a19" to="#a20" type="concepts" ana="#concepts[53]" resp="#paper" cert="0.95">taxonomic scope<term>taxonomic scope</term></span>
      <span xml:id="t82" from="#a19" to="#a20" type="concepts" ana="#concepts[54]" resp="#paper" cert="0.95">automatic mode<term>automatic mode</term></span>
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      <span xml:id="t89" from="#a23" to="#a24" type="concepts" ana="#concepts[61]" resp="#paper" cert="0.95">EC numbers<term>EC numbers</term></span>
      <span xml:id="t90" from="#a23" to="#a24" type="concepts" ana="#concepts[62]" resp="#paper" cert="0.95">BiGG reactions<term>BiGG reactions</term></span>
      <span xml:id="t91" from="#a23" to="#a24" type="concepts" ana="#concepts[63]" resp="#paper" cert="0.95">CAZy terms<term>CAZy terms</term></span>
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      <span xml:id="t107" from="#a29" to="#a30" type="concepts" ana="#concepts[79]" resp="#paper" cert="0.95">functional profiles of metagenomic samples<term>functional profiles of metagenomic samples</term></span>
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      <span xml:id="t110" from="#a13" to="#a14" type="unhoused_relations" ana="#unhoused_relations[0]" resp="#tagger" cert="0.95">ORF detection → Prodigal<note>ORF detection is implemented using Prodigal.</note></span>
      <span xml:id="t111" from="#a3" to="#a4" type="unhoused_relations" ana="#unhoused_relations[1]" resp="#tagger" cert="0.95">eggNOG-mapper → eggNOG database<note>eggNOG-mapper relies on the eggNOG database of orthologous groups.</note></span>
      <span xml:id="t112" from="#a3" to="#a4" type="unhoused_relations" ana="#unhoused_relations[2]" resp="#tagger" cert="0.95">precomputed phylogenies → putative in-paralogs<note>Precomputed phylogenies help minimize annotation transfer from putative in-paralogs.</note></span>
      <span xml:id="t113" from="#a9" to="#a10" type="unhoused_relations" ana="#unhoused_relations[3]" resp="#tagger" cert="0.95">database optimizations → annotation rate<note>Database optimizations, parallelization, and memory-based operation improve annotation rates.</note></span>
      <span xml:id="t114" from="#a9" to="#a10" type="unhoused_relations" ana="#unhoused_relations[4]" resp="#tagger" cert="0.95">memory-based mode → slow I/O disk operations<note>The memory-based mode reduces the impact of slow I/O disk operations.</note></span>
      <span xml:id="t115" from="#a19" to="#a20" type="unhoused_relations" ana="#unhoused_relations[5]" resp="#tagger" cert="0.95">custom annotation databases → specific taxonomic groups<note>Custom annotation databases are constrained to specific taxonomic groups.</note></span>
      <span xml:id="t116" from="#a19" to="#a20" type="unhoused_relations" ana="#unhoused_relations[6]" resp="#tagger" cert="0.95">lineage-specific scopes → orthologs of unwanted lineages<note>Lineage-specific scopes prevent annotation transfer from orthologs of unwanted lineages.</note></span>
      <span xml:id="t117" from="#a25" to="#a26" type="unhoused_relations" ana="#unhoused_relations[7]" resp="#tagger" cert="0.95">de novo PFAM domain annotation → false-positive and negative predictions<note>Realignment refinement reduces false-positive and false-negative domain predictions.</note></span>
      <span xml:id="t118" from="#a29" to="#a30" type="unhoused_relations" ana="#unhoused_relations[8]" resp="#tagger" cert="0.95">annotation of reads → functional profiles of metagenomic samples<note>Direct read annotation can produce functional profiles before assembly.</note></span>
      <span xml:id="t119" from="#a1" to="#a2" type="senses" ana="#senses[0]" resp="#tagger" cert="0.95">eggNOG-mapper v2 as an orthology-based automated functional-annotation workflow for genomic and metagenomic scale</span>
      <span xml:id="t120" from="#a3" to="#a4" type="senses" ana="#senses[1]" resp="#tagger" cert="0.95">orthology-based transfer as using expected function retention in orthologs rather than similarity alone</span>
      <span xml:id="t121" from="#a5" to="#a6" type="senses" ana="#senses[2]" resp="#tagger" cert="0.95">the eggNOG-mapper workflow as prediction, sequence search, orthology inference, and annotation transfer</span>
      <span xml:id="t122" from="#a9" to="#a10" type="senses" ana="#senses[3]" resp="#tagger" cert="0.95">annotation rate as annotated queries per second</span>
      <span xml:id="t123" from="#a15" to="#a16" type="senses" ana="#senses[4]" resp="#tagger" cert="0.95">Diamond mode as the default speed-memory compromise</span>
      <span xml:id="t124" from="#a19" to="#a20" type="senses" ana="#senses[5]" resp="#tagger" cert="0.95">automatic taxonomic scope as the recommended mode for mixed metagenomes</span>
      <span xml:id="t125" from="#a21" to="#a22" type="senses" ana="#senses[6]" resp="#tagger" cert="0.95">pairwise orthology reporting as a quick first pass rather than a substitute for precise inference</span>
      <span xml:id="t126" from="#a25" to="#a26" type="senses" ana="#senses[7]" resp="#tagger" cert="0.95">direct PFAM transfer as low-cost domain prediction with residual false positives and negatives</span>
      <span xml:id="t127" from="#a25" to="#a26" type="senses" ana="#senses[8]" resp="#tagger" cert="0.95">PFAM refinement as realignment of transferred domains to improve accuracy at low cost</span>
      <span xml:id="t128" from="#a29" to="#a30" type="senses" ana="#senses[9]" resp="#tagger" cert="0.95">metagenomic-scale annotation as accepting contigs or reads and emitting functional profiles and decorated feature files</span>
      <span xml:id="t129" from="#a1" to="#a2" type="claim_relations" ana="#claim_relations[0]" resp="#tagger" cert="0.95">extends → eggNOG-mapper version 1<note>note: Version 2 adds databases, performance enhancements, gene prediction, pairwise orthology, domain discovery, and GFF decoration.</note></span>
      <span xml:id="t130" from="#a5" to="#a6" type="claim_relations" ana="#claim_relations[1]" resp="#tagger" cert="0.95">builds-on → eggNOG v5<note>note: The workflow maps input proteins to and transfers annotations from eggNOG v5.</note></span>
      <span xml:id="t131" from="#a33" to="#a34" type="claim_relations" ana="#claim_relations[2]" resp="#tagger" cert="0.95">extends → orthology-based functional annotation<note>note: The paper contributes a more efficient, versatile, and scalable annotation workflow.</note></span>
      <span xml:id="t132" from="#a3" to="#a4" type="concept_edges" ana="#concept_edges[0]" resp="#tagger" cert="0.95">orthology —contrasted-with→ homology detection<note>the relation itself is separately evidenced · strength of the relation: 0.95 · note: Direct rather-than contrast; weight reflects the paper&#x27;s generally-considered qualification. · the relation stated: Function inference via orthology is contrasted with homology detection.</note><term>orthology</term><term>homology detection</term></span>
      <span xml:id="t133" from="#a3" to="#a4" type="concept_edges" ana="#concept_edges[1]" resp="#tagger" cert="0.95">orthologs —contrasted-with→ paralogs<note>the relation itself is separately evidenced · strength of the relation: 0.9 · note: Comparative expectation, not a necessary distinction. · the relation stated: Orthologs are expected to retain function more often than paralogs.</note><term>orthologs</term><term>paralogs</term></span>
      <span xml:id="t134" from="#a7" to="#a8" type="concept_edges" ana="#concept_edges[2]" resp="#tagger" cert="0.95">underlying genome database —causes→ annotation coverage<note>direction on the measure: increases · the relation itself is separately evidenced · strength of the relation: 0.95 · note: Direct increase supported by a reannotation benchmark. · the relation stated: The updated genome database increases annotation coverage.</note><term>underlying genome database</term><term>annotation coverage</term></span>
      <span xml:id="t135" from="#a7" to="#a8" type="concept_edges" ana="#concept_edges[3]" resp="#tagger" cert="0.95">underlying genome database —causes→ phylogenetic resolution<note>direction on the measure: increases · the relation itself is separately evidenced · strength of the relation: 0.95 · note: Direct increase supported by better alignment scores. · the relation stated: The updated genome database increases phylogenetic resolution.</note><term>underlying genome database</term><term>phylogenetic resolution</term></span>
      <span xml:id="t136" from="#a9" to="#a10" type="concept_edges" ana="#concept_edges[4]" resp="#tagger" cert="0.95">eggNOG-mapper —contrasted-with→ Prokka<note>the relation itself is separately evidenced · strength of the relation: 0.95 · note: Direct measured performance comparison. · the relation stated: eggNOG-mapper is benchmarked against Prokka and runs faster, especially on large metagenomic data sets.</note><term>eggNOG-mapper</term><term>Prokka</term></span>
      <span xml:id="t137" from="#a15" to="#a16" type="concept_edges" ana="#concept_edges[5]" resp="#tagger" cert="0.95">Diamond mode —contrasted-with→ MMseqs2 mode<note>the relation itself is separately evidenced · strength of the relation: 1 · note: Direct measured comparison; the numerical size regimes make full strength appropriate. · the relation stated: Diamond and MMseqs2 modes are compared by query-set size, speed, sensitivity, and memory use.</note><term>Diamond mode</term><term>MMseqs2 mode</term></span>
      <span xml:id="t138" from="#a25" to="#a26" type="concept_edges" ana="#concept_edges[6]" resp="#tagger" cert="0.95">native results —distinct-from→ orthology-based predictions<note>the relation itself is separately evidenced · strength of the relation: 1 · note: Explicit independence statement. · the relation stated: Full de novo computation obtains native results independent from orthology predictions.</note><term>native results</term><term>orthology-based predictions</term></span>
      <span xml:id="t139" from="#a1" to="#a2" type="content_tags" ana="#content_tags.findings[0]" resp="#tagger" cert="0.95">eggNOG-mapper v2 adds contig-level gene prediction, pairwise orthology reports, domain discovery, and GFF decoration.</span>
      <span xml:id="t140" from="#a7" to="#a8" type="content_tags" ana="#content_tags.findings[1]" resp="#tagger" cert="0.95">The eggNOG v5 update spans 4.4 million orthologous groups and more than twice as many organisms as the previous version.</span>
      <span xml:id="t141" from="#a7" to="#a8" type="content_tags" ana="#content_tags.findings[2]" resp="#tagger" cert="0.95">Reannotation of 1.75 million proteins increased annotation coverage by 3.23 percent, adding 56,569 annotations.</span>
      <span xml:id="t142" from="#a7" to="#a8" type="content_tags" ana="#content_tags.findings[3]" resp="#tagger" cert="0.95">The expanded database produced significantly better query alignment scores than previous versions.</span>
      <span xml:id="t143" from="#a9" to="#a10" type="content_tags" ana="#content_tags.findings[4]" resp="#tagger" cert="0.95">Despite doubled database size, version 2 improves annotated queries per second by 16 percent on average.</span>
      <span xml:id="t144" from="#a9" to="#a10" type="content_tags" ana="#content_tags.findings[5]" resp="#tagger" cert="0.95">All computational enhancements together improve annotation rates by 608 percent on average over version 1.</span>
      <span xml:id="t145" from="#a9" to="#a10" type="content_tags" ana="#content_tags.findings[6]" resp="#tagger" cert="0.95">eggNOG-mapper runs faster than Prokka, especially on large metagenomic data sets.</span>
      <span xml:id="t146" from="#a15" to="#a16" type="content_tags" ana="#content_tags.findings[7]" resp="#tagger" cert="0.95">Diamond iterate mode is twofold faster than MMseqs2 at one million queries and threefold faster at ten million.</span>
      <span xml:id="t147" from="#a15" to="#a16" type="content_tags" ana="#content_tags.findings[8]" resp="#tagger" cert="0.95">MMseqs2 is faster than Diamond for query sets up to 100,000 at comparable sensitivity.</span>
      <span xml:id="t148" from="#a19" to="#a20" type="content_tags" ana="#content_tags.findings[9]" resp="#tagger" cert="0.95">Lineage-specific scopes prevent functional transfer from unwanted lineages.</span>
      <span xml:id="t149" from="#a25" to="#a26" type="content_tags" ana="#content_tags.findings[10]" resp="#tagger" cert="0.95">Direct PFAM transfer has an F1 score of 89.7 percent with little computational cost.</span>
      <span xml:id="t150" from="#a25" to="#a26" type="content_tags" ana="#content_tags.findings[11]" resp="#tagger" cert="0.95">Realignment refinement raises PFAM F1 to 98.9 percent while keeping computational cost low.</span>
      <span xml:id="t151" from="#a31" to="#a32" type="content_tags" ana="#content_tags.findings[12]" resp="#tagger" cert="0.95">The workflow emits decorated GFF, tabular annotations, orthology assignments, and taxonomic placements.</span>
      <span xml:id="t152" from="#a1" to="#a2" type="content_tags" ana="#content_tags.definitions[0]" resp="#tagger" cert="0.95">an orthology-based automated functional-annotation workflow optimized for large genomic and metagenomic data sets<term>eggNOG-mapper v2</term></span>
      <span xml:id="t153" from="#a9" to="#a10" type="content_tags" ana="#content_tags.definitions[1]" resp="#tagger" cert="0.95">annotated queries per second<term>annotation rate</term></span>
      <span xml:id="t154" from="#a19" to="#a20" type="content_tags" ana="#content_tags.definitions[2]" resp="#tagger" cert="0.95">the annotation-transfer scope recommended for mixed metagenomic data sets<term>taxonomic scope</term></span>
      <span xml:id="t155" from="#a19" to="#a20" type="content_tags" ana="#content_tags.definitions[3]" resp="#tagger" cert="0.95">a scope that prevents transfer from orthologs in unwanted lineages<term>lineage-specific scope</term></span>
      <span xml:id="t156" from="#a21" to="#a22" type="content_tags" ana="#content_tags.definitions[4]" resp="#tagger" cert="0.95">a quick first-pass query-to-genome orthology result adjustable by taxa and ortholog type<term>orthology reports</term></span>
      <span xml:id="t157" from="#a7" to="#a8" type="content_tags" ana="#content_tags.quantities[0]" resp="#tagger" cert="0.95">4.4 million OGs — orthologous groups in the synchronized eggNOG v5 genome database</span>
      <span xml:id="t158" from="#a7" to="#a8" type="content_tags" ana="#content_tags.quantities[1]" resp="#tagger" cert="0.95">1.75 million proteins — random human-gut catalog subsample used for reannotation</span>
      <span xml:id="t159" from="#a7" to="#a8" type="content_tags" ana="#content_tags.quantities[2]" resp="#tagger" cert="0.95">3.23% — increase in annotation coverage over version 1</span>
      <span xml:id="t160" from="#a7" to="#a8" type="content_tags" ana="#content_tags.quantities[3]" resp="#tagger" cert="0.95">56,569 — newly annotated proteins in the coverage benchmark</span>
      <span xml:id="t161" from="#a9" to="#a10" type="content_tags" ana="#content_tags.quantities[4]" resp="#tagger" cert="0.95">16% — average annotation-rate gain despite doubled database size</span>
      <span xml:id="t162" from="#a9" to="#a10" type="content_tags" ana="#content_tags.quantities[5]" resp="#tagger" cert="0.95">608% — average combined annotation-rate improvement over version 1</span>
      <span xml:id="t163" from="#a15" to="#a16" type="content_tags" ana="#content_tags.quantities[6]" resp="#tagger" cert="0.95">1,000,000 — query-set size where Diamond iterate is twice as fast as MMseqs2</span>
      <span xml:id="t164" from="#a15" to="#a16" type="content_tags" ana="#content_tags.quantities[7]" resp="#tagger" cert="0.95">10,000,000 — query-set size where Diamond iterate is three times faster than MMseqs2</span>
      <span xml:id="t165" from="#a15" to="#a16" type="content_tags" ana="#content_tags.quantities[8]" resp="#tagger" cert="0.95">100,000 — upper query-set size where MMseqs2 is faster at comparable sensitivity</span>
      <span xml:id="t166" from="#a25" to="#a26" type="content_tags" ana="#content_tags.quantities[9]" resp="#tagger" cert="0.95">89.7% — F1 score for direct ortholog transfer of PFAM domains</span>
      <span xml:id="t167" from="#a25" to="#a26" type="content_tags" ana="#content_tags.quantities[10]" resp="#tagger" cert="0.95">98.9% — F1 score after PFAM realignment refinement</span>
      <span xml:id="t168" from="#a7" to="#a8" type="content_tags" ana="#content_tags.variables[0]" resp="#tagger" cert="0.95">annotation coverage<term>annotation coverage</term></span>
      <span xml:id="t169" from="#a7" to="#a8" type="content_tags" ana="#content_tags.variables[1]" resp="#tagger" cert="0.95">alignment scores<term>alignment scores</term></span>
      <span xml:id="t170" from="#a9" to="#a10" type="content_tags" ana="#content_tags.variables[2]" resp="#tagger" cert="0.95">annotation rate<term>annotation rate</term></span>
      <span xml:id="t171" from="#a19" to="#a20" type="content_tags" ana="#content_tags.variables[4]" resp="#tagger" cert="0.95">taxonomic scope<term>taxonomic scope</term></span>
      <span xml:id="t172" from="#a21" to="#a22" type="content_tags" ana="#content_tags.variables[5]" resp="#tagger" cert="0.95">target taxa<term>target taxa</term></span>
      <span xml:id="t173" from="#a11" to="#a12" type="content_tags" ana="#content_tags.variables[6]" resp="#tagger" cert="0.95">specificity<term>specificity</term></span>
      <span xml:id="t174" from="#a11" to="#a12" type="content_tags" ana="#content_tags.variables[7]" resp="#tagger" cert="0.95">recall<term>recall</term></span>
      <span xml:id="t175" from="#a11" to="#a12" type="content_tags" ana="#content_tags.variables[8]" resp="#tagger" cert="0.95">F 1 score<term>F 1 score</term></span>
    </spanGrp>
  </standOff>
  <text>
    <body>
        <p><anchor xml:id="a0"/> eggNOG-mapper v2: Functional Annotation, Orthology Assignments, and Domain Prediction at the Metagenomic Scale</p>
        <p>Abstract</p>
        <p><anchor xml:id="a1"/>Even though automated functional annotation of genes represents a fundamental step in most genomic and metagenomic workflows, it remains challenging at large scales. Here, we describe a major upgrade to eggNOG-mapper, a tool for functional annotation based on precomputed orthology assignments, now optimized for vast (meta)genomic data sets. Improvements in version 2 include a full update of both the genomes and functional databases to those from eggNOG v5, as well as several efficiency enhancements and new features. Most notably, eggNOG-mapper v2 now allows for: 1) de novo gene prediction from raw contigs, 2) built-in pairwise orthology prediction, 3) fast protein domain discovery, and 4) automated GFF decoration. eggNOG-mapper v2 is available as a standalone tool or as an online service at http://eggnog-mapper.embl.de<anchor xml:id="a2"/> .</p>
        <p>Introduction</p>
        <p><anchor xml:id="a3"/>Inference of gene function via orthology, rather than by homology detection, is generally considered the most reliable approach for transferring functional information between molecular sequences, as orthologs are expected to retain function more often than paralogs ( Gabaldón and Koonin 2013 ; Glover et al. 2019 ). However, since delineating orthology is highly demanding (both computationally and algorithmically), most automated methods rely on homology-based annotations ( Götz et al. 2008 ; Seemann 2014 ; Blum et al. 2021 ). EggNOG-mapper relies on the eggNOG database ( Huerta-Cepas et al. 2019 ) of orthologs groups (OGs), covering thousands of bacterial, archaeal, and eukaryotic organisms. For this, it takes advantage of the precomputed phylogenies inferred for each OG to efficiently refine orthology assignments and therefore minimize the transferring of annotations from putative in-paralogs. The method was originally proven to provide more accurate predictions than homology-based approaches ( Huerta-Cepas et al. 2017 ), while preserving computational performance at the genomic and metagenomic scale. Here, we present eggNOG-mapper v2, a major upgrade featuring improvements in annotation coverage, overall performance, and program capabilities<anchor xml:id="a4"/> ( fig. 1 ).</p>
        <p><anchor xml:id="a5"/>Workflow and new features of eggNOG-mapper v2. ( A ) The gene prediction stage uses Prodigal to perform protein prediction from assembled contigs. ( B ) During the search stage, HMMER3, Diamond, or MMseqs2 can be used to align the input proteins to eggNOG v5. ( C ) During the orthology inference stage, a report of orthologs is generated based on the desired taxonomic scope. ( D ) Finally, protein annotations and domains are transferred from orthologs to the queries and reported as tabular and GFF files<anchor xml:id="a6"/>.</p>
        <p>Coverage and Performance Improvements</p>
        <p><anchor xml:id="a7"/>The underlying genome database has been updated to be in sync with eggNOG v5, spanning 4.4 million OGs and more than twice the number of organisms than in the previous version. This improvement increases annotation coverage and phylogenetic resolution, particularly noticeable when analyzing large metagenomic data sets. For instance, the reannotation of 1.75 million proteins randomly subsampled from a human-gut metagenomic gene catalog ( Almeida et al. 2021 ) yielded a 3.23% increase in annotation coverage (56,569 newly annotated proteins), compared with eggNOG-mapper version 1. The phylogenetic resolution was also improved, obtaining significantly better alignment scores for the query sequences than previous versions<anchor xml:id="a8"/> (Wilcoxon test W = 1.2E + 12, P -value &lt; 2.2E − 16). <anchor xml:id="a9"/>Moreover, although the underlying databases have doubled in size, eggNOG-mapper v2 improves the annotation rate (annotated queries per second) by 16% on average, compared with previous versions. The most important changes regarding computational enhancements relate to database optimizations, allowing for faster queries and parallelization, and a new memory-based mode that significantly reduces the impact of slow I/O disk operations. Taken together, these changes improve annotation rates by 608% on average, with respect to eggNOG-mapper v1 ( fig. 2 A ). Compared with Prokka ( Seemann 2014 ), one of the fastest annotation tools available for prokaryotic genomes according to recent benchmarks ( Shaffer et al. 2020 ), eggNOG-mapper runs faster, especially on large metagenomic data sets<anchor xml:id="a10"/> ( fig. 2 B ).</p>
        <p><anchor xml:id="a11"/>Performance of eggNOG-mapper v2. ( A ) average minutes to annotate input proteomes. EggNOG-mapper v2 (blue) against eggNOG-mapper v1 (red). ( B ) average minutes to annotate input genomes. EggNOG-mapper v2 (blue) against Prokka (green). ( C ) average minutes (in log scale) to annotate input proteins. MMseqs2 (-s 2,4,6; black) against Diamond (iterate/sensitive mode; orange). ( D ) Specificity (Sp), recall (Re), and F 1 score, of PFAM domain annotation either from direct transference from orthologs, or after realignment. Full de novo realignment results were used as reference. ( E ) average minutes for PFAM domain annotation, using either PFAM full de novo (brown) or realign to orthologs domains (blue) modes. Benchmark setup: tests in ( A ) and ( B ) were done on 20 sets of 1–100 random proteomes ( A ) or genomes ( B ) from ( Almeida et al. 2021 ), and executed using 10 CPUs and 80 GB of RAM. Tests in ( C ) were done on 35 random sets of 10–10,000,000 proteins from Progenomes v2 ( Mende et al. 2020 ), using 30 CPUs and 240 GB of RAM. Tests in ( Dm ) and ( E ) as in ( C ), only for sets of 10–100,000 proteins<anchor xml:id="a12"/>.</p>
        <p>ORF Prediction</p>
        <p><anchor xml:id="a13"/>Another major capability added to the new eggNOG-mapper workflow is predicting ORFs directly from assembled contigs ( fig. 1 A ). ORF detection, only available for prokaryotic assemblies, is performed using Prodigal ( Hyatt et al. 2010 ), which provides the protein sequences to be used by eggNOG-mapper for functional annotation. Prodigal modes (“normal,” “anonymous,” and “training”) as well as custom translation tables can be further chosen by the user<anchor xml:id="a14"/>.</p>
        <p>Sequence Mapping Modes</p>
        <p><anchor xml:id="a15"/>Additionally, we have broadened the options for the initial sequence-mapping step carried out by eggNOG-mapper ( fig. 1 B ). Now, Diamond, MMseqs2, and HMMER3 ( Mistry et al. 2013 ) modes are available, each recommended for different use cases. The default Diamond mode provides the best balance between speed and memory consumption. EggNOG-mapper v2 also implements the new Diamond mode ‘–iterate’, which iteratively applies different levels of sensitivity. Using the new –iterate mode, Diamond is twice as fast as MMseqs2 for query sets of 1,000,000, and three times faster for 10,000,000 sequences. The MMseqs2 mode provides faster results than Diamond ( fig. 2 C ) for query sets up to 100,000 sequences for comparable sensitivity<anchor xml:id="a16"/>. <anchor xml:id="a17"/>When input data are nucleotide sequences, a direct translation is done assuming they represent coding sequences starting in an open reading frame. Alternatively, both Diamond and MMseqs2 can be executed in blastx-like mode, particularly useful when using sequencing reads as input data. For the annotation of long, error-prone sequencing reads, the frameshift option of Diamond can also be enabled. The HMMER3 mode is significantly slower than the other two and requires heavy databases to be downloaded. However, HMM-based searches might aid in the annotation of sequences for which distant homology relationships against the eggNOG v5 OGs cannot be detected by Diamond and MMseqs modes<anchor xml:id="a18"/>.</p>
        <p>Adjusting Taxonomic Scopes</p>
        <p><anchor xml:id="a19"/>Another new feature now available with eggNOG-mapper v2 is the possibility of creating custom annotation databases constrained to specific taxonomic groups. For instance, users could easily create databases spanning only their domain or phylum of interest, therefore reducing computational times of subsequent annotation jobs. Moreover, the new version provides enhanced options to control the taxonomic scope ( fig. 1 C ) used for transferring functional annotations, which can be adjusted from automatic mode (recommended for mixed metagenomic data sets) to lineage-specific scopes (preventing transferring functional terms from orthologs of unwanted lineages)<anchor xml:id="a20"/>.</p>
        <p>Orthology Reports</p>
        <p><anchor xml:id="a21"/>Taking advantage of the rapid orthology assignments performed by eggNOG-mapper, it is now possible to report pairwise orthology relationships for each query against any of the genomes covered by eggNOG v5 ( fig. 1 C ). Although this feature is not intended to substitute more precise orthology prediction methods, it provides a very quick and simple “first-pass” approach to obtain pairwise relationships between query sequences and all eggNOG v5 organisms. Orthology reports can be further adjusted by specifying the target taxa and the type of orthologs to be reported (i.e., one-to-one, many-to-many)<anchor xml:id="a22"/>.</p>
        <p>Annotation Sources</p>
        <p><anchor xml:id="a23"/>In order to provide an integrated report of functional annotations per query, eggNOG-mapper v2 offers new annotation sources and improved reports ( fig. 1 D ). The functional annotation sources, which provide different levels of coverage ( supplementary fig. S1 , Supplementary Material online), are: predicted protein name; KEGG pathways, modules, and orthologs ( Kanehisa et al. 2017 ); Gene Ontology labels ( Gene Ontology Consortium 2018 ); EC numbers, BiGG reactions ( Norsigian et al. 2020 ); CAZy terms ( Lombard et al. 2014 ); COG functional categories ( Tatusov et al. 2000 ); eggNOG OGs; and free text descriptions at all taxonomic levels. Reports are generated in tab-delimited and/or XLSX file formats. Moreover, when ORF prediction mode is enabled, proteins used to annotate are reported in FASTA format, together with a functionally decorated GFF file. Alternatively, eggNOG-mapper annotation reports can be used to decorate any custom GFF file<anchor xml:id="a24"/>.</p>
        <p>Protein Domain Annotations</p>
        <p><anchor xml:id="a25"/>Along with the functional terms annotated per query, this new version of eggNOG-mapper provides PFAM ( Mistry et al. 2021 ) and SMART ( Letunic et al. 2021 ) protein domain predictions. PFAM domain annotations are by default transferred from the inferred orthologs with very little impact on computational cost, but also with a small proportion of false-positive and negative predictions (F1 score 89.7%, fig. 2 D ). Optionally, de novo PFAM domain annotation is also available at large scales, both as a refinement phase for the orthology-based predictions (thus keeping the computational cost very low, while eliminating the risk of false positives; F 1 score 98.9%, fig. 2 D ) or by full computation (obtaining native results independent from orthology predictions). When using the de novo approach, HMMER3 searches are executed using in-memory mode for higher efficiency. Moreover, GA-based thresholds and PFAM clan disambiguation are automatically applied. Performance comparisons between the different modes are shown in figure 2 E<anchor xml:id="a26"/>.</p>
        <p>Features Comparison with Other Functional Annotation Tools</p>
        <p>Although accuracy and performance are the main goal of eggNOG-mapper v2, other practical differences might motivate its use, or not, compared with alternative software. Those practical issues include the type of input and output data, the functional sources used to annotate query sequences, and the target taxonomic scope of each program.</p>
        <p><anchor xml:id="a27"/>EggNOG-mapper is tightly bound to the eggNOG database, which covers a wide range of prokaryotic and eukaryotic organisms, and provides normalized functional annotations from multiple sources (see previous sections). As eggNOG is based on a curated selection of representative species spanning the whole tree of life, it provides a broad annotation coverage while keeping redundancy low<anchor xml:id="a28"/>. Other tools use smaller reference databases (e.g., SwissProt [ UniProt Consortium 2021 ]) for general functional annotations but incorporate niche-specific functional databases for specific purposes. For instance, Prokka is suited for the annotation for prokaryotic-only genomes and includes the detection of tRNAs, transposases and signal peptides (which are not specifically targeted by eggNOG-mapper). DRAM ( Shaffer et al. 2020 ) and MicrobiomeAnnotator ( Ruiz-Perez et al. 2021 ) use broad annotation sources for microbial data sets such as KOFam/KEGG classification. Both provide optional mappings to large protein reference databases comparable to eggNOG (e.g., trEMBL or Uniref90), but at the cost of more computational resources and time ( Ruiz-Perez et al. 2021 ). In the case of DRAM, additional genomic features can be annotated, including rRNAs, tRNAs, peptidases, and carbohydrate-active enzymes. Mantis ( Queirós et al. 2021 ) and InterProScan allow users to annotate sequences based on multiple HMM-based database sources, including eggNOG, PFAM, or PANTHER ( Mi et al. 2010 ).</p>
        <p><anchor xml:id="a29"/>On the other hand, this new version of eggNOG-mapper is particularly focused on improving the annotation process at the metagenomic scale. For instance, it incorporates the possibility of using Prodigal for the automatic prediction of open reading frames (ORFs) out of raw contigs. Those options are not commonly available in other annotation tools, with only Prokka and DRAM providing similar capabilities. Moreover, eggNOG-mapper v2 allows for the direct annotation of reads via blastx-like searches, which is not a recommended mode in terms of accuracy, but it offers the possibility of obtaining functional profiles of metagenomic samples before assembling<anchor xml:id="a30"/>.</p>
        <p><anchor xml:id="a31"/>Regarding outputs, eggNOG-mapper is optimized for large-scale annotation jobs, producing GFF files decorated with functional annotations, tab-delimited files with the predicted functional terms per query, orthology assignment tables and taxonomic placements. Other tools provide similar output files (except for the orthology and taxonomic predictions), with only DRAM and MicrobiomeAnnotator providing further statistics and graphical outputs summarizing the results. Notably, Prokka can be set to produce Genbank and Sequin files compliant with the Genbank/ENA/DDJB format, thus facilitating the uploading of annotated genomes to public databases<anchor xml:id="a32"/>.</p>
        <p>Conclusions</p>
        <p><anchor xml:id="a33"/>Overall, eggNOG-mapper v2 provides a more efficient, versatile, and scalable automated functional annotation workflow than its predecessor. Standalone versions are available at GitHub ( https://github.com/eggnogdb/eggnog-mapper ), together with extensive documentation and usage examples ( https://github.com/eggnogdb/eggnog-mapper/wiki ). For convenience, an online service for the annotation of large genomic and metagenomic data sets is also available at http://eggnog-mapper.embl.de<anchor xml:id="a34"/> .</p>
        <p>Supplementary Material</p>
        <p>Supplementary data are available at Molecular Biology and Evolution online.</p>
        <p>Supplementary Material</p>
        <p>Click here for additional data file.<anchor xml:id="a35"/></p>
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