%0 Journal Article
%T The uncertain consequences of transferring bacterial strains between laboratories - rpoS instability as an example
%A Beny Spira
%A Rodrigo de Almeida Toledo
%A Ram P Maharjan
%A Thomas Ferenci
%J BMC Microbiology
%D 2011
%I BioMed Central
%R 10.1186/1471-2180-11-248
%X We found that samples of the E. coli K-12 strain MC4100TF exchanged on three separate occasions by mail between our laboratories became heterogeneous. Reconstruction studies indicated that LB-stabs exhibited mutations previously found in GASP studies in stationary phase LB broth. At least 40% of reconstructed stocks and an equivalent proportion of actually mailed stock contained these mutations. Mutants with low RpoS levels emerged within 7 days of incubation in the stabs. Sequence analysis of ten of these segregants revealed that they harboured each of three different rpoS mutations. These mutants displayed the classical phenotypes of bacteria lacking rpoS. The genetic stability of MC4100TF was also tested in filter disks embedded in glycerol. Under these conditions, GASP mutants emerge only after a 3-week period. We also confirm that the intrinsic high RpoS level in MC4100TF is mainly due to the presence of an IS1 insertion in rssB.Given that many E. coli strains contain high RpoS levels similar to MC4100TF, the integrity of such strains during transfers and storage is questionable. Variations in important collections may be due to storage-transfer related issues. These results raise important questions on the integrity of bacterial archives and transferred strains, explain variation like in the ECOR collection between laboratories and indicate a need for the development of better methods of strain transfer.Well-resourced culture collections distribute bacteria mostly as freeze-dried ampoules [1,2]. On the other hand, most research labs generally do not exchange lyophilized cultures and over the past 50 years a good proportion of bacterial exchanges were either in agar stabs or on impregnated glycerolized discs, as also used by the Coli Genetic Stock Center (CGSC). Generally, comparison of storage and shipping conditions test for viability and all of the above methods work well in this regard for Escherichia coli. Recently however, we became concerned about hetero
%U http://www.biomedcentral.com/1471-2180/11/248