Induction of DnaK upon γ-Irradiation at High and Low Rates in Escherichia coli

DnaK is implicated in protein folding, repair and degradation. Its protective role during heat shock is well documented and many other stresses can also induce its production. Using a competitive ELISA, intracellular DnaK concentrations were determined in Escherichia coli ATCC 25922 exposed to a γ-irradiation dose of 0.3 KGy applied either at high (8 × 10 KGy/min) or low rates (3 × 10 KGy/min) and with or without a recuperation period of 22 h at 37 ̊C post-treatment. All four irradiation treatments reduced cell counts similarly and significantly compared to the control (P < 0.0001). However, the highest DnaK concentration was observed in cells irradiated at low rate without recuperation (105,416 molecules/cell; P = 0.0001). Furthermore, DnaK levels remained higher than the control (38,500 molecules/ cell) after the recuperation period (P < 0.05). Variation in the intracellular DnaK concentration indicates that the bacterial stress response was modulated differently according to the irradiation treatment (P = 0.0001).