Extensive gene acquisition in the extremely psychrophilic bacterial species Psychroflexus torquis and the link to sea-ice ecosystem specialism

• Published in: Genome Biology and Evolution
• Main Authors: Feng, S, Powell, SM, Wilson, R, Bowman, JP
• Format: Article in Journal/Newspaper
• Language: English
• Published: Oxford University Press 2014
• Subjects: Biological Sciences; Microbiology; Microbial Ecology; Arctic; Sea ice
• Online Access: https://doi.org/10.1093/gbe/evt209; http://www.ncbi.nlm.nih.gov/pubmed/24391155; http://ecite.utas.edu.au/88505

Sea ice is a highly dynamic and productive environment that includes a diverse array of psychrophilic prokaryotic and eukaryotic taxadistinct from the underlying water column. Because sea ice has only been extensive on Earth since the mid-Eocene, it has beenhypothesized that bacteria highly adapted to inhabit sea ice have traits that have been acquired through horizontal gene transfer(HGT). Here we compared the genomes of the psychrophilic bacterium Psychroflexus torquis ATCC 700755 T , associated with bothAntarctic and Arctic sea ice, and its closely related nonpsychrophilic sister species, P. gondwanensis ACAM 44 T . Results show thatHGT has occurredmuchmore extensively in P. torquis in comparison to P. gondwanensis . Genetic features that can be linked to thepsychrophilic and sea ice-specific lifestyle of P. torquis include genes for exopolysaccharide (EPS) and polyunsaturated fattyacid (PUFA) biosynthesis, numerous specific modes of nutrient acquisition, and proteins putatively associated with ice-binding,light-sensing (bacteriophytochromes), and programmed cell death (metacaspases). Proteomic analysis showed that several genesassociated with these traits are highly translated, especially those involved with EPS and PUFA production. Becausemost of the genesrelating to the ability of P. torquis to dwell in sea-ice ecosystems occur on genomic islands that are absent in closely related P. gondwanensis , its adaptation to the sea-ice environment appears driven mainly by HGT. The genomic islands are rich in pseudogenes,insertional elements, and addiction modules, suggesting that gene acquisition is being followed by a process of genomereduction potentially indicative of evolving ecosystem specialism.