Changes in the proteome of Escherichia coli during growth at 15 °C after incubation at 2, 6 or 8 °C for 4 days

For better understanding of the complex behaviour of Escherichia coli at chiller temperatures, log phase E. coli grown at 15 °C were incubated at 8, 6, or 2 °C for 4 days, and were then incubated at 15 °C for 12 h. Cultures were sampled after incubation at the lower temperatures, and during subsequent incubation at 15 °C. Proteins extracted from the samples were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Spots of 45 previously identified proteins that were differentially expressed at 15 or ≤ 8 °C were quantified by image analysis. After incubation at 8 or 6 °C for 4 days cells were growing with or without formation of elongated cells (filaments), respectively, but growth did not occur at 2 °C. In cells incubated at 8 or 6 °C proteins associated with the stress response and energy generation were upregulated and proteins associated with protein synthesis were downregulated, while protein levels in cells incubated at 2 °C were little changed. When cells were then incubated at 15 °C, the levels of differentially expressed proteins in cells that had been incubated at 8 or 6 °C decreased or increased towards the levels found in cells growing at 15 °C, but some proteins were still under or over expressed after 12 h. In cells incubated at 15 °C after incubation at 2 °C, the levels of many of the proteins declined but the levels of proteins associated with protein synthesis increased. The findings indicate that the physiological states of log phase E. coli incubated at ≤ 2 °C or at higher chiller temperature are different, but that for both states incubation at an above chiller temperature for > 3 generations is required before protein levels adjusted to those usual for the higher temperature. Cells in these different physiological states may respond differently to other stresses encountered during warming of chilled foods.