On the induction of protective responses in Salmonella typhimurium strain TA1535/pSK1002 by UVA (365 nm).
Exposure to UVA (365 nm) led to growth delay, loss of viability and inhibition of 3H-thymidine incorporation into the cells of Salmonella typhimurium strain TA1535 containing multiple copies of a plasmid pSK1002 carrying a umuC'-'lacZ fusion gene. Ultraviolet-A induced umu gene expression, as monitored by the estimation of beta-galactosidase, in a linear fluence-dependent manner. The induction of umu gene expression increased with the increase of postirradiation incubation period of the cells in the LB-ampicillin (LBA) medium at 37 degrees C and leveled off from 2 h onward. The induction of gene expression depended on concomitant protein synthesis and represented the induction of the SOS response in the particular S. typhimurium cells used. The exposure to low fluences (sublethal) of UVA also led to the induction of an adaptive response in the same bacterial cells, which made them resistant to subsequent challenge by a much higher fluence of the same radiation. The adaptive response, as monitored by the assays of viability and beta-galactosidase units, increased with the period of exposure to sublethal fluences of UVA, attained a maximum at the UVA exposure of 4.5 kJ/m2 (15 min) and thereafter gradually decreased with further increase of UVA exposure period. Modulation studies involving D2O, LBA growth medium, different scavengers of free radicals and quenchers of activated oxygen species indicated the involvement of both hydroxyl free radicals and singlet oxygen in the UVA-induced umu gene expression.
Rahman
S
S
Biophysics Division, Saha Institute of Nuclear Physics, Calcutta, India.
Bose
B
B
Chatterjee
S N
SN
D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D004261:DNA Replication / Q000528:radiation effects; D004259:DNA-Directed DNA Polymerase; D029968:Escherichia coli Proteins; D015870:Gene Expression / Q000528:radiation effects; D005798:Genes, Bacterial / Q000528:radiation effects; D007700:Kinetics; D010957:Plasmids / Q000528:radiation effects; D012486:Salmonella typhimurium / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D013936:Thymidine / Q000378:metabolism; D014466:Ultraviolet Rays; D001616:beta-Galactosidase / Q000096:biosynthesis
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C078202:UmuC protein, E coli; D004259:DNA-Directed DNA Polymerase; D001616:beta-Galactosidase; D013936:Thymidine