Physiological effects of sunlight on Bacillus subtilis strains with varying capacity to repair photoproducts

: Nonlethal doses of sunlight were established to cause a growth delay in Bacillus subtilis strain 1201 possessing an unimpaired repair system. This effect was not observed with the 1201-10 uvr1 mutant deficient in DNA excision repair; however, addition of an extract of uvr1+ cells restorated the phenomenon of growth delay by sunlight in this mutant. Experiments with glass light filters showed that a weakened growth delay in strain 1201 could also be produced by rays of sunlight with wavelengths greater than 380 nm. Maximum growth delay was observed after irradiation with the complete spectrum of sunlight. Experiments with the protein synthesis inhibitor chloramphenicol indicated that sunlight promotes synthesis of proteins preventing the dying of cells. The presence of Casamino acids is favorable for the synthesis of protective proteins.