Horizontal gene transfer drives extreme physiological change in Haloarchaea

TL;DR

This study reveals that horizontal gene transfer from bacteria significantly contributed to the extreme physiological adaptations of haloarchaea, transforming their metabolic capabilities from anaerobic methanogens to aerobic heterotrophs.

Contribution

It provides evidence that horizontal gene transfer played a crucial role in the major physiological evolution of haloarchaea from their methanogenic ancestors.

Findings

Nearly half of the haloarchaeal genes have bacterial origins.

Horizontal gene transfer facilitated key phenotypic changes.

Haloarchaeal evolution involved extensive gene acquisition from bacteria.

Abstract

The haloarchaea are aerobic, heterotrophic, photophosphorylating prokaryotes, whose supposed closest relatives and ancestors, the methanogens, are CO2-reducing, anaerobic chemolithotrophs. Using two available haloarchaeal genomes we firstly confirmed the methanogenic ancestry of the group and then investigated those individual genes in the haloarchaea that differ in their phylogenetic signal to this relationship. We found that almost half the genes, about which we can make strong statements, have bacterial ancestry and are likely a result of multiple horizontal transfer events. Futhermore their functions specifically relate to the phenotypic changes required for a chemolithotroph to become a heterotroph. If this phylogenetic relationship is correct, it implies the development of the haloarchaeal phenotype was among the most extreme changes in cellular physiology fuelled by horizontal gene transfer.