The Ultraviolet Photochemistry and Photobiology of Vegetative Cells and Spores of Bacillus megaterium

Abstract

The ultraviolet (UV) photochemistry and photobiology of spores and vegetative cells of Bacillus megaterium have been studied. The response of vegetative cells of B. megaterium appears qualitatively similar to those of Escherichia coli, Micrococcus radiodurans, and Bacillus subtilis with respect to photoproduct formation and repair mechanisms. UV irradiation, however, does not produce cyclobutane-type thymine dimers in the DNA of spores, although other thymine photo-products are produced. The photoproducts do not disappear after photoreactivation, but they are eliminated from the DNA by a dark-repair mechanism different from that found for dimers in vegetative cells. Irradiations performed at three wavelengths produce the same amounts of spore photoproduct and give the same survival curves. Variation of the sporulation medium before irradiation results in comparable alterations in the rate of spore photoproduct production and in survival.

Effects of Mn and Fe Levels on Bacillus subtilis Spore Resistance and Effects of Mn 2+ , Other Divalent Cations, Orthophosphate, and Dipicolinic Acid on Protein Resistance to Ionizing Radiation

“…Each gel is representative of two or three independent trials conducted for each reaction-irradiation mixture. (20). The results with ␣ Ϫ ␤ Ϫ spores having different Mn levels were largely, but not completely, similar to those with wild-type spores, even though ␣ Ϫ ␤ Ϫ spores were more sensitive than wild-type spores to all the agents tested, as expected.…”

Ultraviolet irradiation of DNA complexed with alpha/beta-type small, acid-soluble proteins from spores of Bacillus or Clostridium species makes spore photoproduct but not thymine dimers.

“…Studies on the UV photochemistry of DNA under various conditions in vitro led to the conclusion that the production of pyrimidine dimers was characteristic of DNA in the B conformation, whereas SP formation was favored in DNA in the A conformation (8,9). This led to the suggestion that DNA in dormant spores might be in the A conformation (8).…”

“…Indeed, the yields for TT in vegetative cells and SP in spores are similar, and extremely high levels (>25% of total thymine) of SP can accumulate in DNA (2). Rather, the dormant spore has at least two mechanisms that efficiently eliminate SP in the early minutes of spore germination; one of these mechanisms is specific for SP (6, 7).Studies on the UV photochemistry of DNA under various conditions in vitro led to the conclusion that the production of pyrimidine dimers was characteristic of DNA in the B conformation, whereas SP formation was favored in DNA in the A conformation (8,9). This led to the suggestion that DNA in dormant spores might be in the A conformation (8).…”

Characterization of a New Thermophilic Spore Photoproduct Lyase from Geobacillus stearothermophilus (SplG) with Defined Lesion Containing DNA Substrates

“…In addition, UV irradiation of spores gives rise to different DNA lesions (7). Although in normal cells mostly cyclobutane pyrimidine dimers and (6-4) lesions (8) are formed, in spores the unusual photoproduct 5-thyminyl-5,6-dihydrothymine (SP), 2 depicted in Scheme 1 (7,9), is exclusively generated (10). These differences in the photoreactivity may be because of an unusual packing of the DNA in spores (1,11,12) and the high amounts of dipicolinic acid (DPA) present in spores (13).…”