Action Spectra for the Ultraviolet and Visible Light Inactivation of Phage T7: Effect of Host-Cell Reactivation

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Abstract
Kinetics of the inactivation of phage T7 by 6 UV and visible light wavelengths of the far (below 320 nm) and the near UV (above 320 nm) were studied, with and without host-cell [Escherichia coli] reactivation. Inactivations were always exponential with the 3 shorter wavelengths (254, 313 and 334 nm), whereas with the longer wavelengths (365, 405 and 460 nm), a small shoulder (extrapolation number < 2) was consistently obtained. The host-cell reactivation sector was prominent with 254 and 313 nm of radiation, reduced with 334 nm and trivial or absent with the 3 longer wavelengths. Action spectra for the inactivation revealed small shoulders in the near-UV region, with and without host-cell reactivation. A comparison of single-strand break (alkali-labile bond) induction by 365 nm of radiation in phage T4, compared with lethality in phage T7, revealed that a frequency of 0.3 single-strand breaks may occur per lethal hit.