DNA is preserved and maintains transforming potential after contact with
brines of the deep anoxic hypersaline lakes of the Eastern Mediterranean Sea

Sara Borin, Elena Crotti, Francesca Mapelli, Isabella Tamagnini, Cesare
Corselli and Daniele Daffonchio

Saline Systems 2008, 4:10doi:10.1186/1746-1448-4-10

Published: 5 August 2008

Abstract (provisional)

Background
Extracellular dissolved DNA has been demonstrated to be present in many
terrestrial and aquatic environments, actively secreted, or released by
decaying cells. Free DNA has the genetic potential to be acquired by living
competent cells by horizontal gene transfer mediated by natural
transformation. Aim of this work is to study the persistence of
extracellular DNA and its biological transforming activity in extreme
environments like the deep hypersaline anoxic lakes of the Mediterranean
Sea. The brine lakes are separated from the upper seawater by a steep
chemocline inhabited by stratified prokaryotic networks, where cells sinking
through the depth profile encounter increasing salinity values and osmotic
stress.

Results
Seven strains belonging to different taxonomic groups isolated from the
seawater-brine interface of four hypersaline lakes were grown at medium
salinity and then incubated in the brines. The osmotic stress induced the
death of all the inoculated cells in variable time periods, between 2 hours
and 144 days, depending on the type of brine rather than the taxonomic group
of the strains, i.e. Bacillaceae or gamma-proteobacteria. The Discovery lake
confirmed to be the most aggressive environment toward living cells. In all
the brines and in deep seawater dissolved plasmid DNA demonstrated to be
substantially preserved for a period of 32 days in axenic conditions.
L'Atalante and Bannock brines induced a decrease of the supercoiled form up
to 70 and 40%% respectively, in the other brines only minor changes in
plasmid conformation were observed. Plasmid DNA after incubation in the
brines demonstrated to maintain the capacity to transform naturally
competent cells of Acinetobacter baylii strain BD413.

Conclusions
Free dissolved DNA is likely to be released by the lysis of cells induced by
osmotic stress in the deep hypersaline anoxic lakes. Naked DNA was
demonstrated to be preserved and biologically active in these extreme
environments, and hence could constitute a genetic reservoir of traits
acquirable by horizontal gene transfer.

Source: BMC Evolutionary Biology [Open Access Paper]
http://www.salinesystems.org/content/4/1/10

Posted by
Robert Karl Stonjek