Genes controlling carotenoid synthesis were cloned from Erwinia herbicola and expressed in an Escherichia coli strain. Carotenoids protect against high fluences of near-UV (NUV; 320 to 400 nm) but not against far-UV (200-300 nm). Protection of E. coli cells was not observed following treatment with either psoralen or 8-methoxypsoralen plus NUV. However, significant protection of cells producing carotenoids was observed with three photosensitizing molecules activated by NUV (alpha-terthienyl, harmine, and phenylheptatriyne) which are thought to have the membrane as an important lethal target. Protection of carotenoid-producing cells against inactivation was not observed with acridine orange plus visible light but was seen with toluidine blue O plus visible light.

Mutations in the Escherichia coli katF gene (hydroperoxidase II) result in sensitivity to inactivation by H202 and broad-spectrum near-UV (NUV; 300 to 400 nm) radiation. Another mutation, nur, originally described as conferring sensitivity to inactivation by broad-spectrum and monochromatic NUV, also confers sensitivity to inactivation by H202. Genetic analysis via transduction suggests that the nur mutation is a mutant allele of the katF locus. As previously reported for broad-spectrum and monochromatic NUV wavelengths, the sensitivity of a particular strain to H202 inactivation is also independent of the recA and uvrA alleles. Extracts of nur and katF strains lack catalase (hydroperoxidase II) as revealed by polyacrylamide gels stained for such activity, which is consistent with the genetic results.The mutagenic and inactivating effects of both monochromatic and broad-spectrum near-UV (NUV) wavelengths (300 to 400 nm) have been the subject of numerous investigations, which have been extensively reviewed (10,13,17,18,40).A mutation in an Escherichia coli gene (nur) has been described which sensitizes cells to inactivation by NUV without affecting sensitivity to far-UV (FUV) inactivation (35-37). Specifically, it was shown that the recA13, recAl, and uvrA6 mutations did not affect the sensitivity of stationary-phase cells to NUV inactivation. However, the polAl mutation did influence the sensitivity of E. coli cells to inactivation by NUV in an nur+ genetic background (36). The fact that the polAl mutation sensitizes E. coli to NUV inactivation and that E. coli xthA mutants (exonuclease III deficient) are sensitive to inactivation by H202 (8) and NUV (31) might mean that repair of or protection against NUVand H202-induced damage is based on a complex oxidative defense system (4).Further evidence that H202 is involved in NUV inactivation comes from the observation that incorporation of bovine catalase into the plating medium or the irradiated cell suspension protects E. coli cells from both inactivation and mutagenesis by broad-spectrum NUV (32). Hartman (14) has also presented evidence that H202 is involved with NUV inactivating events in stationary-phase E. coli cells.Pretreatment of E. coli or Salmonella typhimurium cells with a sublethal concentration of H202 results in protection against inactivation by a lethal concentration of H202 (4, 7) as well as by broad-spectrum NUV (33, 39). Tyrrell (39) has shown that pretreatment of growing E. coli cells with low fluences of NUV protects against inactivation by H202. If H202 were one product of NUV irradiation in cells, it would be expected that cells lacking catalase should be sensitive to inactivation by NUV. Recently, Leowen and his colleagues have described mutants which are defective in catalase activity (21)(22)(23). In this paper, we present evidence that lesions in the katF gene, but not the katE or katG gene, result in sensitivity to broad-spectrum NUV as well as to * Corresponding author.

Abstract— Stationary cells of isogenic pairs of Escherichia coli K12 strains presumably differing only in the recA function have been inactivated with near‐UV (300–400 nm) radiation. Based on near‐UV inactivation kinetics, the strains can be divided into two discrete categories in which near‐UV sensitivity does not necessarily correlate with far‐UV sensitivity conferred by two different recA alleles. Lack of overlap between near‐UV and far‐UV (recA) sensitivity can be explained hy assuming that a different chromosomal gene (nur) controls near‐UV sensitivity. Support for this hypothesis comes from a mating experiment in which four selected recombinants, isogenic with respect to auxotrophic markers, were identified exhibiting all four possible combinations of far‐UV (recA1 vs recA +) and near‐UV sensitivity (nur vs nur+). Transduction with phase P1 has shown that introduction of the recA1 allele into a recA+ recipient does not affect the near‐UV sensitivity of the recipient. Additional matings together with transduction experiments suggest that the nur gene is located at a position on the E. coli linkage map clearly separable from recA (minute 58).

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Phototoxicity of five naturally occurring P-carboline alkaloids was assayed against a series of Escherichia coli strains and against the insect Trichoplusia ni (Lepidoptera: Noctuidae). Rank order efficacy of the compounds was comparable in both organisms. Although the bacterial assay demonstrated oxygen dependence, the degree of phototoxicity did not correlate with the relative efficiency of in vitro singlet oxygen or hydrogen peroxide photoproduction by the alkaloids. A better correlation was observed between chromatographic migration distances (lipophilicity) and phototoxicity. Therefore, hydrophobic mechanisms in which the alkaloids diffuse with varying efficiencies into cells or into the vicinity of target molecules may be important modes of phototoxicity for these compounds