Two different strains of Saccharomyces cerevisiae were used: Pho91 and Rmd5. Both strains were genetically modified to express an endonuclease upon growth on galactose-containing culture media, which inserts double-strand breaks at two defined sites of the genome. These two sites flank the TRP1 gene, which allows cells to synthesize tryptophan (an amino acid). Thus, successful insertion of the two double-strand breaks removes this gene and makes the cells tryptophan-auxotrophic. The two strains differ in the location of the double-strand breaks on the chromosome.
The following groups were used: 1) exposure of the Pho91 strain to the 50 Hz magnetic field, 2) exposure of the Rmd5 strain to the 50 Hz magnetic field, 3) control group of the Pho91 strain, 4) control group of the Rmd5 strain.
|Setup||Helmholtz coils were 40 cm in diameter and consisted of 154 turns of 1.4 mm copper wire, coil centers 20 cm apart, mounted on a wooden frame, connected in series and axial directed, so that the magnetic currents flow perpendicular to the surface of the culture plates; plates were located in the region within the coils where the fields’ homogeneity was high (±3%); the temperature was measured periodically and a difference of 0.5°C between control and exposed samples was observed, with 29°C as the mean temperature of plates; the control cultures were located in a thermostatic plastic box, 5 m apart from the coils at the same temperature; the background magnetic field in the room at control location was 0.68 μT, the geomagnetic field was 42.95 µT|
Exposure to the magnetic field led to a significant increase in the number of cell colonies in the Pho91 strain (group 1; 1.29-fold increase) and Rmd5 strain (group 2; 1.5-fold increase) after 21 days compared to the control groups. DNA repair was significantly higher on day 15 for the Rmd5 strain (55.56-fold) and for the Pho91 strain (1.18-fold) compared to the control groups.
The authors conclude that exposure of Saccharomyces cerevisiae to a 50 Hz magnetic field might increase DNA repair. Differences in repair kinetics between different strains might be related to the position of the DNA damage and the distance to the centromere.