No evidence for extensive horizontal gene transfer in the genome of the tardigrade Hypsibius dujardini

Georgios Koutsovoulos, Sujai Kumar, Dominik R Laetsch, Lewis Stevens, Jennifer Daub, Claire Conlon, Habib Maroon, Fran Thomas, Aziz A Aboobaker, Mark Blaxter

Research output: Contribution to journalArticlepeer-review

Abstract

Tardigrades are meiofaunal ecdysozoans that are key to understanding the origins of Arthropoda. Many species of Tardigrada can survive extreme conditions through cryptobiosis. In a recent paper [Boothby TC, et al. (2015) Proc Natl Acad Sci USA 112(52):15976-15981], the authors concluded that the tardigrade Hypsibius dujardini had an unprecedented proportion (17%) of genes originating through functional horizontal gene transfer (fHGT) and speculated that fHGT was likely formative in the evolution of cryptobiosis. We independently sequenced the genome of H. dujardini. As expected from whole-organism DNA sampling, our raw data contained reads from nontarget genomes. Filtering using metagenomics approaches generated a draft H. dujardini genome assembly of 135 Mb with superior assembly metrics to the previously published assembly. Additional microbial contamination likely remains. We found no support for extensive fHGT. Among 23,021 gene predictions we identified 0.2% strong candidates for fHGT from bacteria and 0.2% strong candidates for fHGT from nonmetazoan eukaryotes. Cross-comparison of assemblies showed that the overwhelming majority of HGT candidates in the Boothby et al. genome derived from contaminants. We conclude that fHGT into H. dujardini accounts for at most 1-2% of genes and that the proposal that one-sixth of tardigrade genes originate from functional HGT events is an artifact of undetected contamination.

Original languageEnglish
Pages (from-to)5053-5058
Number of pages6
JournalProceedings of the National Academy of Sciences
Volume113
Issue number18
Early online date24 Mar 2016
DOIs
Publication statusPublished - 3 May 2016

Keywords

  • blobtools
  • contamination
  • horizontal gene transfer
  • metagenomics
  • tardigrade

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