Spectral impact of inactivating light on photoreactivation of Escherichia coli

The spectral impact of inactivating light on subsequent photoreactivation of Escherichia coli K12 was investigated. Ultraviolet-induced pyrimidine dimers in the genome of E. coli were determined, while the survival of E. coli was also examined. A medium-pressure UV lamp (MP: 220-580 nm) was equipped with an optical bandpass filter with the peak emission at 230 run, 254 nm, or 300 nm, in order to characterize the photoreactivation properties. As references, a MP lamp without a filter, a MP lamp with a glass plate (MPG: 300-580 nm), and a low-pressure UV lamp (LP: 254 nm) were also used for inactivation. Medium pressure inactivation at 230 nm, 254 nm, or 300 nm was followed by the photoreactivation of survival ratio, which was comparable to that after LP exposure. Meanwhile, a repressed survival recovery was observed after MP or MPG inactivation. It was therefore indicated that the MP lamp was effective at repressing photoreactivation of E. coli, which was not attributable to the specific MP emission either at 230 nm, 254 nm, or 300 nm. Rather, the simultaneous exposure to broad wavelengths might provide the MP lamp with the repair repressive effect.