Effects of extremely low-frequency electromagnetic fields on bacteria - The question of a co-stressing factor

Different strains of bacteria (Escherichia coli, Proteus vulgaris, Photobacterium phosphoreum, Photobacterium fisheri) were exposed to extremely low-frequency electromagnetic fields in the frequency range 2-50 Hz. The field strength was varied from 1 to 10 mT using sinusoidal wave forms. The duration of exposure and temperature were varied. The growth, protein synthesis and luminescence of the bacteria were examined. No effect could be seen on the protein synthesis rate in 19 experiments using radioactively labelled leucine. The protein pattern was not affected in 15 experiments under standard temperature conditions using isoelectric focusing (IEF) and sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE). The growth of E. coli K12 was reduced by a maximum of 3.8% in 2 out of 23 experiments. The luminescence of the photobacteria was affected in 2 out of 20 experiments at standard temperature. Combining electromagnetic fields with heat stress, effects on the protein pattern and luminescence were observed in more than 50% of the experiments. The results support the concept that bacteria are quite resistant to electromagnetic fields, probably because of compensation and self-regulation. The role of an electromagnetic field as a co-stressing factor is discussed.