Spontaneous conversion between mutL and 6 bpDeltamutL in Salmonella typhimurium LT7: association with genome diversification and possible roles in bacterial adaptation.
Previously, we reported the phenomenon of genome diversification in Salmonella typhimurium LT7, i.e., individual strains derived from LT7 kept changing the genome structure by inversions, translocations, duplications, and mutations. To elucidate the genetic basis, we sequenced selected genes of the mismatch repair (MMR) system for correlations between MMR defects and genome diversification. We chose S. typhimurium LT7 mutants 8111F2 and 9052D1 for mut gene sequence analyses and found that both mutants had a deletion of one of three tandem 6-bp repeats, GCTGGC GCTGGC GCTGGC, within mutL, which was designated 6 bpDeltamutL. mutS and mutH genes were unchanged in the mutants analyzed. Some sublines of 8111F2 and 9052D1 spontaneously stopped the genome diversification process at certain stages during single-colony restreaking passages, and in these strains the 6 bpDeltamutL genotype also became wild-type mutL. We conclude that conversion between mutL and 6 bpDeltamutL occurs spontaneously and that transient defects of mutL facilitate genome diversification without leading to the accumulation of multiple detrimental genetic changes. Spontaneous conversion between mutL and 6 bpDeltamutL may be an important mechanism used by bacteria to regulate genetic stability in adaptation to changing environments.
Gong
Jun
J
Department of Microbiology, Peking University Health Science Center, Beijing 100083, China.
Liu
Wei-Qiao
WQ
Liu
Gui-Rong
GR
Chen
Fang
F
Li
Jun-Qian
JQ
Xu
Guo-Min
GM
Wang
Ling
L
Johnston
Randal N
RN
Eisenstark
Abraham
A
Liu
Shu-Lin
SL
D000220:Adaptation, Biological / Q000235:genetics*; D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000502:physiology*; D001483:Base Sequence; D017353:Gene Deletion; D005798:Genes, Bacterial; D014644:Genetic Variation; D016680:Genome, Bacterial; D042822:Genomic Instability / Q000235:genetics; D008969:Molecular Sequence Data; D051719:MutS DNA Mismatch-Binding Protein / Q000235:genetics; D030781:Organisms, Genetically Modified; D012486:Salmonella typhimurium / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid
D000251:Adenosine Triphosphatases; D051719:MutS DNA Mismatch-Binding Protein