Genetic analysis of the photoreactivation system in Pseudomonas cepacia

点击翻译按钮获取中文摘要

Pseudomonas cepacia was initially described as a phytopathogen. However, association of this bacterium, as an opportunistic pathogen, with human infections has been now well documented. In 1975, Carson and Petersen noted, for a P.cepacia strain of natural origin, a potent photoreactivation. This would pose a serious problem in hospitals where contaminations of aseptic solutions, anesthetics, a transplantation tissue and surgical equipments by P.cepacia have been reported. Thus, this purpose was aimed at knowing the genetic organization of the photoreactivation in P.cepacia. A clinical isolate of P.cepacia, strain PCJ, was selected as being suitable for the study from among about 100 strains.In wild-type strain of the P.cepacia, a potent photoreactivation was indeed demonstrated for the cells exposed to ultraviolet( UV ), that is, number of colonies on the plates incubated in the light were 10^2 to 10^4 times larger than that of the plates kept in the dark at a same temperature. Sevente … More en mutants that were sensitive to UV could be derived from the wild-type cells treated with methanesulfonic acid ethyl ester( EMS ). In marked contrast to the wild-type, when the mutant cells were exposed to UV, they were all nearly unable to form colony both in the light and in the dark, suggesting that they lost the photoreactivating activity. No difference was seen between the wild-type and the UV-sensitive mutants in their susceptibility to EMS and N-methyl-N'-nitro -N-nitrosoguanidine. With respect to the ability to survive from the exposure to UV, a close resemblance was observed between the wild-type cells of P.cepacia and those of the E.coli with a uvra mutation. These results indicated that in P.cepacia photoreactivation was playing a very important role, if not unique, in repairing the damage of DNA caused by UV irradiation. With the intention of cloning the gene(s) that participating in the photoreactivation, attempts were made to isolate, from a chromosomal gene library of the P.cepacia, any clone that complements a phr ( photoreactivation ) mutation of a E.coli. A clone that could do so has been found and this suggested that there would be a photoreactivation system in P.cepacia which functions biochemically in a manner that is similar to that of E.coli. Subcloning of the gene(s) concerned is in progress. Less