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The genome of a subterrestrial nematode reveals an evolutionary strategy for adaptation to heat

By Deborah J Weinstein, Sarah E Allen, Maggie C. Y. Lau, Mariana Erasmus, Kathryn C Asalone, Kathryn Walters-Conte, Gintaras Deikus, Robert Sebra, Gaetan Borgonie, Esta van Heerden, Tullis C. Onstott, John R. Bracht

Posted 28 Aug 2019
bioRxiv DOI: 10.1101/747584

The nematode Halicephalobus mephisto was originally discovered inhabiting a deep terrestrial aquifer 1.3 km underground. H. mephisto can thrive under conditions of abiotic stress including heat and minimal oxygen, where it feeds on a community of both chemolithotrophic and heterotrophic prokaryotes in an unusual ecosystem isolated from the surface biosphere. Here we report the comprehensive genome and transcriptome of this organism, identifying a signature of adaptation: an expanded repertoire of 70 kilodalton heat-shock proteins (Hsp70) and avrRpt2 induced gene 1 (AIG1) proteins. We find that positive selection has driven the expansion of Hsp70 genes, which are also transcriptionally induced upon growth under heat stress. We further show that AIG1 may have been acquired by horizontal gene transfer (HGT) from a rhizobial fungus. Over one-third of the genes of H. mephisto are novel, highlighting the divergence of this nematode from other sequenced organisms. This work sheds light on the genomic strategies of adaptation to heat in the first complete subterrestrial eukaryotic genome.

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