Journal of Bacteriology, August 2000, p. 4375-4379, Vol. 182, No. 16
Cancer Research Center, Columbia, Missouri
65201
Received 1 May 2000/Accepted 17 May 2000
Long-term survival under limited growth conditions presents
bacterial populations with unique environmental challenges. The existence of Salmonella enterica serovar Typhimurium
cultures undisturbed in sealed nutrient agar stab vials for 34 to 45 years offered a unique opportunity to examine genetic variability under natural conditions. We have initiated a study of genetic changes in
these archival cultures. We chose to start with examination of the
rpoS gene since, among gram-negative bacteria, many genes needed for survival are regulated by RpoS, the stationary-phase sigma
factor. In each of 27 vials examined, cells had the rpoS start codon UUG instead of the expected AUG of Salmonella
and Escherichia coli strains recorded in GenBank. Ten of
the 27 had additional mutations in the rpoS gene compared
with the X77752 wild-type strain currently recorded in GenBank. The
rpoS mutations in the 10 strains included two deletions as
well as point mutations that altered amino acid sequences
substantially. Since these stored strains were derived from ancestral
cells inoculated decades ago and remained undisturbed, it is assumed
that the 10 rpoS mutations occurred during storage. Since
the remaining 17 sequences were wild type (other than in the start
codon), it is obvious that rpoS remained relatively stable
during decades of sealed storage.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
rpoS Mutants in Archival Cultures of
Salmonella enterica Serovar Typhimurium
*
Corresponding author. Mailing address: Cancer Research
Center, 3501 Berrywood Drive, Columbia, MO 65201. Phone: (573)
875-2255. Fax: (573) 443-1202. E-mail:
eisenstarkA{at}missouri.edu.
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