Effect of UV Irradiation on Macromolecular Synthesis and Colony Formation in Bacteroides fragilis

Abstract

Irradiation of Bacteroidesfiagilis cells with far-UV light resulted in the immediate, rapid and extensive degradation of DNA which continued for 40 to 60 min after irradiation. During the degradation phase, DNA synthesis was decreased but was never totally inhibited. DNA degradation after irradiation was inhibited by chloramphenicol and caffeine. DN'4 synthesis in irradiated cells was reduced by chloramphenicol but resumed after 100 min at the same exponential rate as in irradiated cells without chloramphenicol. Irradiated cells continued to synthesize DNA for 40 min in the presence of caffeine but after this time DNA synthesis was completely inhibited and never recovered. RNA and protein synthesis were decreased by UV irradiation and the degree of inhibition was proportional to the UV dose. Colony formation was not affected immediately by UV irradiation and continued for a dose-dependent period before inhibition. There was an inverse relationship between UV dose and inhibition of colony formation which occurred sooner in cells irradiated with lower doses of UV light. The characteristics of DNA synthesis in B. jiagilis cells after UV irradiation differ from those in wild-type Escherichia coli cells, where DNA synthesis is stopped immediately by UV irradiation, but resemble those in E. colirecA mutant cells where extensive degradation occurs following UV irradiation.

Pyrimidine Dimer Excision Repair of DNA in Bacteroides fragilis Wild-type and Mitomycin C-sensitive/UV-sensitive Mutants

“…luteus dimer spec@ endonuclease Although B. fragilis has been shown to incorporate exogenous radiolabelled thymidine into DNA (Schumann et al, 1984), the level of incorporation is insufficient to allow excision repair studies involving radiolabelled thymine dimers at low UV doses. An alternative approach (Campbell & Yasbin, 1984) using the pyrimidine dimer specific M. luteus endonuclease (Riazzudin & Grossman, 1977) was made to detect the presence of pyrimidine dimers in the UVirradiated DNA.…”