Escherichia coli strains containing plasmid-borne fusions of the recA promoter-operator region to the Vibrio fischeri lux genes were previously shown to increase their luminescence in the presence of DNA damage hazards, and thus to be useful for genotoxicant detection. The present study expands previous work by demonstrating and investigating the luminescent response of these strains to ultraviolet radiation. Several genetic variants of the basic recA'::lux design were examined, including a tolC modification of membrane efflux capacity, a chromosomal integration of the recA'::lux fusion, a different lux reporter (Photorhabdus luminescens instead of V. fischeri, allowing the assay to be run at 37 degrees C), and a different host bacterium (Salmonella typhimurium instead of E. coli). Generally, two modifications provided the fastest responses: the use of the S. typhimurium host or the P. luminescens lux reporter. Highest sensitivity, however, was demonstrated in an E. coli strain in which a single copy of the V. fischeri lux fusion was integrated into the bacterial chromosome.