Ultraviolet sensitivity of Vibrio parahaemolyticus, a causative bacterium of food poisoning

Hyperthermic effects on DNA repair of UV-irradiated Dictyostelium discoideum

DNA repair of a lower eukaryote, Dictyostelium discoideum, has been investigated through the analysis of heat effects on cell mortality and DNA repair of UV-irradiated amoeboid cells. In a wild-type strain (NC4), an increase in temperature immediately after UV irradiation resulted in an increase in cell mortality, though similar heat treatment before UV irradiation had no such effect. Similar results were obtained in another wild-type strain, HPS83. In NC4, heat treatment after UV irradiation did not inhibit the nicking of DNA strands during excision repair processes, but did inhibit the rejoining of the DNA strand breaks. Removal of thymine-containing pyrimidine dimers from DNA molecules was also depressed by heat treatment after UV irradiation. In contrast, heat treatment before UV irradiation had no effect on any stage of the nicking process, the excision of the dimers or the rejoining. On the other hand, a radiation-sensitive mutant (TW8) defective in an incision step of the excision repair process did not show an increase in cell mortality in response to heat treatment administered either before or after UV irradiation. Though the optimum temperature for cell growth of the amoebae was 23 degrees C, the critical temperature for effective enhancement of cell killing was ca. 30 degrees C. Hence we assume that the excision repair of UV-damaged DNA is selectively sensitive to heat treatment.

Induction of phage-like particles from a pathogenic strain of Vibrio parahaemolyticus by mitomycin C

A rapid drop of absorbance of cell suspensions due to cell lysis was observed midway in cell growth of a pathogenic strain, Vibrio parahaemolyticus WP1, when the cells were incubated in a growth medium containing mitomycin C. We succeeded in isolating phage-like particles from the cell lysate, but not from that of the non-pathogenic strain, WP28. The purified particle has a clear-cut envelope and is hexagonal in shape with no tail. The size of particles is about 65 millimicrons on the diagonal and about 250 S. The particles contained one kind of protein of 45,000 dalton.

An ovulation inducing agent containing clomiphene citrate causes DNA-strand breaks without SOS responses in Escherichia coli

Effects of Clomid, an ovulation-inducing drug containing clomiphene citrate, on Escherichia coli were investigated. Radiation-sensitive mutants, uvrA and recA, were more sensitive to Clomid than the parental wild-type strain. DNA synthesis in these two strains was more depressed by Clomid than that in the wild-type strain. Clomid caused DNA-strand breaks, but few SOS responses such as mutation, induction of prophage and expression of the umuC+ gene were induced.