High level of intergenera gene exchange shapes the evolution of haloarchaea in an isolated Antarctic lake

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: DeMaere, MZ, Williams, TJ, Allen, MA, Brown, MV, Gibson, JAE, Rich, J, Lauro, FM, Dyall-Smith, M, Davenport, KW, Woyke, T, Kyrpides, NC, Tringe, SG, Cavicchioli, R
• Format: Article in Journal/Newspaper
• Language: English
• Published: Natl Acad Sciences 2013
• Subjects: Biological Sciences; Genetics; Molecular Evolution; Antarctic; Antarc*; Antarctica
• Online Access: https://doi.org/10.1073/pnas.1307090110; http://www.ncbi.nlm.nih.gov/pubmed/24082106; http://ecite.utas.edu.au/88990

Deep Lake in Antarctica is a globally isolated, hypersaline systemthat remains liquid at temperatures down to −20 C. By analyzingmetagenome data and genomes of four isolates we assessed genomevariation and patterns of gene exchange to learn how thelake community evolved. The lake is completely and uniformlydominated by haloarchaea, comprising a hierarchically structured,low-complexity community that differs greatly to temperate andtropical hypersaline environments. The four Deep Lake isolatesrepresent distinct genera (∼85% 16S rRNA gene similarity and∼73% genome average nucleotide identity) with genomic characteristicsindicative of niche adaptation, and collectively account for∼72% of the cellular community. Network analysis revealed a remarkablelevel of intergenera gene exchange, including the sharingof long contiguous regions (up to 35 kb) of high identity(∼100%). Although the genomes of closely related Halobacterium,Haloquadratum, and Haloarcula (>90% average nucleotide identity)shared regions of high identity between species or strains, thefour Deep Lake isolates were the only distantly related haloarchaeato share long high-identity regions. Moreover, the Deep Lakehigh-identity regions did not match to any other hypersaline environmentmetagenome data. The most abundant species, tADL,appears to play a central role in the exchange of insertion sequences,but not the exchange of high-identity regions. The genomiccharacteristics of the four haloarchaea are consistent with a lakeecosystem that sustains a high level of intergenera gene exchangewhile selecting for ecotypes that maintain sympatric speciation. Thepeculiarities of this polar system restrict which species can grow andprovide a tempo and mode for accentuating gene exchange.