The existence in our laboratory of

The existence in our laboratory of over 10 000 Sulmonella typhimurium LT2 cultures sealed in agar stab vials for 33-46 years offers an opportunity for evolutionary and mutational studies. In each of 77 vials examined, 10(3)-10(2) colony forming units per vial were recovered (less than 0.01% of the original population) even after decades of undisturbed storage. Considerable genetic variability was observed in these populations. Three genetic variables, chromosome fragment size as determined by pulsed-field gel electrophoresis, extensive mutational reversions from nutritional auxotrophy to prototrophy, and differences in protein content as assayed by sodium dodecyl sulfate polyacrylamide gel electrophoresis, were measured. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.