pH induced damage and repair in E. coli

Escherichia coli lost its colony-forming ability when suspended in Tris/NaOH or Tris/Mg2+ buffers of pH 10.0 and 4.0, respectively. A significant decrease in the survival of radiation-sensitive mutants recA, polA, res, rer and lexA was observed as compared to their wild-type counterpart under these conditions. The alkali-injured cells were found to recover when incubated at 37 degrees C for 2 h in 0.05 M phosphate buffer of pH 8.0, whereas no such liquid holding recovery was observed in recA and lexA mutants. Recovery in phosphate buffer was not affected by metabolic inhibitors. As a result of alkali treatment, the sensitivity of bacteria to ultraviolet light (UV) was enhanced. However, on incubation for 2 h in recovery buffer at 37 degrees C, the bacteria regained partial UV resistance. Bacteria exposed to alkaline environment exhibited an enhanced level of mutagenesis. Contrary to the treated wild-type, the mutants recA and lexA did not exhibit any increase in the mutation frequency. Alkali treatment to GC----AT transition mutants of Salmonella typhimurium, TA102 and TA104 resulted in the highest number of revertants per plate.