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This study examined the microbicidal activity of 222 nm UV radiation (UV), which is potentially a safer alternative to the 254 nm UV radiation (UV) that is often used for surface decontamination. Spores and/or growing and stationary phase cells of , , , and , and a Herpes virus were all killed or inactivated by UV, and at lower fluences than with UV spores and cells lacking the major DNA repair protein RecA were more sensitive to UV, as were spores lacking their DNA protective proteins, the α/β-type small, acid-soluble spore proteins. The spore cores’ large amount of Ca-dipicolinic acid (∼25% of core dry wt) also protected and spores against UV, while spores’ proteinaceous coat may have given some slight protection against UV Survivors of spores treated with UV acquired a large number of mutations, and this radiation generated known mutagenic photoproducts in spore and cell DNA – primarily cyclobutane-type pyrimidine dimers in growing cells, and an α-thyminyl-thymine adduct termed the spore photoproduct (SP) in spores. Notably, loss of a key SP repair protein markedly decreased spore UV resistance. UV-treated spores germinated relatively normally, and generation of colonies from these germinated spores was not salt-sensitive. The latter two findings suggest that UV does not kill spores by general protein damage, and thus the new results are consistent with the notion that DNA damage is responsible for killing of spores and cells by UV Spores of a variety of bacteria are resistant to common decontamination agents, and many of them are major causes of food spoilage and some serious human diseases, including anthrax caused by spores of Consequently, there is an ongoing need for efficient methods for spore eradication, in particular methods that have minimal deleterious effects on people or the environment. Ultraviolet radiation (UV) at 254 nanometers (UV) is sporicidal and commonly used for surface decontamination, but can cause deleterious effects in humans. Recent work, however, suggests that 222 nm UV (UV) may be less harmful to people than UV, yet still kill bacteria and at lower fluences than UV The current work has identified the damage by UV that leads to killing of growing cells and spores of some bacteria many of which are human pathogens, and UV also inactivates a Herpes virus.