Cell density dependent response of E. coli cells to weak ELF magnetic fields

The effects of weak magnetic fields of extremely low frequency (ELF) on E. coli K12 AB1157 cells were studied by the method of anomalous viscosity time dependencies (AVTD). E. coli cells at different densities within a range of 5 x 10(5)-10(9) cell/ml were exposed to ELF (sinusoidal, 30 microT peak, 15 min) at a frequency of 9 Hz. A transient effect with maximum 40-120 min after exposure was observed. Kinetics of the per-cell-normalised ELF effects fitted well to a Gaussian distribution for all densities during exposure. A maximum value of these kinetics and a time for this maximum were strongly dependent on the cell density during exposure. These data suggest a cell-to-cell interaction during response to ELF. Both dependencies had three regions close to a plateau within the ranges of 3 x 10(5) - 2 x 10(7) cell/ml, 4 x 10(7) - 2 x 10(8) cell/ml and 4 x 10(8)-10(9) cell/ml and two rather sharp transitions between these plateaus. The effect reached a maximum value at a density of 4 x 10(8) cell/ml. Practically no effect was observed at the lowest density of 3 x 10(5) cell/ml. The data suggested that the ELF effect was mainly caused by a secondary rather than a primary reaction. The filtrates from exposed cells neither induced significant AVTD changes in unexposed cells nor increased the ELF effect when were added to cells before exposure. The data did not provide evidence for significant contribution of stable chemical messengers, but some unstable compounds such as radicals could be involved in the mechanism of cell-to-cell interaction during response to ELF. The results obtained were also in accordance with a model based on an re-emission of secondary photons during resonance fluorescence.