title: Stress-induced beta-lactam antibiotic resistance mutation and sequences of stationary-phase mutations in the Escherichia coli chromosome.
abstract: In some enterobacterial pathogens, but not in Escherichia coli, loss-of-function mutations are a common route to clinically relevant beta-lactam antibiotic resistance. We previously constructed an assay system for studying enterobacterial beta-lactam resistance mutations using the well-developed genetics of E. coli by integrating enterobacterial ampRC genes into the E. coli chromosome. Like the cells of other enterobacteria, E. coli cells acquire beta-lactam resistance by ampD mutation. Here we show that starvation and stress responses provoke ampD beta-lactam resistance mutagenesis. When starved on lactose medium, Lac(-) strains used in mutagenesis studies accumulate ampD beta-lactam resistance mutations independent of Lac reversion. DNA double-strand break repair (DSBR) proteins and the SOS and RpoS stress responses are required for this mutagenesis, in agreement with the results obtained for lac reversion in these cells. Surprisingly, the stress-induced ampD mutations require DinB (DNA polymerase IV) and partially require error-prone DNA polymerase V, unlike lac mutagenesis, which requires only DinB. This assay demonstrates that real-world stressors, such as starvation, can induce clinically relevant resistance mutations. Finally, we used the ampD system to observe the true forward-mutation sequence spectrum of DSBR-associated stress-induced mutagenesis, for which previously only frameshift reversions were studied. We found that base substitutions outnumber frameshift mutations, as seen in other experimental systems showing stress-induced mutagenesis. The important evolutionary implication is that not only loss-of-function mutations but also change-of-function mutations can be generated by this mechanism.
authors: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030-3411, USA.
authors: Joseph F
authors: JF
authors: Petrosino
authors: Rodrigo S
authors: RS
authors: Galhardo
authors: Liza D
authors: LD
authors: Morales
authors: Susan M
authors: SM
authors: Rosenberg
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D002244:Carbon / Q000172:deficiency / Q000502:physiology; D002876:Chromosomes, Bacterial / Q000235:genetics*; D004252:DNA Mutational Analysis; D004259:DNA-Directed DNA Polymerase / Q000235:genetics / Q000502:physiology; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology; D016368:Frameshift Mutation; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics / Q000502:physiology; D009154:Mutation / Q000235:genetics*; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics; D018440:beta-Lactam Resistance / Q000235:genetics*
chemical_list: D001426:Bacterial Proteins; C094399:DinB protein, E coli; D029968:Escherichia coli Proteins; D002244:Carbon; C120926:DNA polymerase V, E coli; D004259:DNA-Directed DNA Polymerase; C062460:AmpD protein, Bacteria; D009238:N-Acetylmuramoyl-L-alanine Amidase