Inducible plasmid-mediated copper resistance in Escherichia coli

The copper resistance in Escherichia coli determined by plasmid pRJ1004 is inducible. The level of resistance is proportional to the inducing dose of copper. The level of copper resistance in induced and uninduced cells changes with the growth phase of the culture. Induced resistant cells accumulate less copper than uninduced cells, so that reduced accumulation may be the mechanism of resistance. We propose that the inducible plasmid-coded copper resistance interacts with the normal metabolism of the cell to protect against toxic levels of copper while allowing continued operation of copper-dependent functions.

Are there female heterogametic strains of Chironomus tentans Fabricius?

Although male heterogamety is the generally accepted method of sex determination in Chironomus, female heterogamety has been reported for some strains of Chironomus tentans. Some new data, combined with a reassessment of the published data, indicate that the proposal of female heterogamety rests on inconclusive data, while male heterogamety provides an adequate explanation of sex determination in C. tentans. A cross which would unambiguously discriminate between male and female heterogamety in these strains is proposed, although it is considered unlikely that female heterogamety exists in this species.

A mutant of Pseudomonas aeruginosa deficient in an ATP-dependent deoxyribonuclease

A mutant of Pseudomonas aeruginosa PAO1 originally isolated on the basis of its sensitivity to methyl methanesulphonate was found to be (i) sensitive to u.v.- and gamma-irradiation, (ii)deficient in recombination as assayed by transduction and conjugation and (iii) deficient in an ATP-dependent deoxyribonuclease activity. Its marker (mms-13) is cotransducible with argB and pyrE which are mapped at approximately 22 min on the P. aeruginosa chromosome.

Imogene King's conceptual framework: a proposed model for continuing nursing education

This paper presents a proposed model for continuing nursing education based on Imogene King's conceptual framework. The rationale for using King's conceptual framework as the foundation underlying this proposed model is three-fold: the concepts--social systems, health, perception, and interpersonal relationships--are relevant in every nursing situation; the interacting levels of operation--individuals, groups, and society--depict a reciprocal relationship between human behaviour and the environment; and the triad of elements--continuing nursing education, nursing practice, and nursing research--are interrelated in the nursing profession. The authors contend that this approach to continuing nursing education is beneficial to participating nurses, the health care consumer, and to the advancement of the nursing profession. Based on its simplicity and flexibility, the proposed intra-systems model described in this article is useful as a systematic guide for continuing nursing education. The authors believe that this proposed model provides an approach for stimulating continued learning, for establishing innovative foundations for nursing practice, and for generating inquiry through research. Utilizing this approach in maintaining the educational standards for professional practice will promote change for the advancement of the nursing profession.

Effect of repair deficiency and R plasmids on spontaneous and radiation-induced mutability in Pseudomonas aeruginosa

The effect of R plasmids on spontaneous and radiation (ultraviolet and gamma)-induced mutability in Pseudomonas aeruginosa was studied in strains containing the radiation-sensitive markers polA3 or rec-2 and the revertable auxotrophic markers hisO27 and trpB1. In the absence of an R plasmid, the radiation-induced mutability was dependent on the recA+ genotype and independent of the polA+ genotype, whereas spontaneous mutability was similar in all genetic backgrounds. R plasmids pPL1, R2, and pMG15 increased the ultraviolet radiation survival and ultraviolet-induced mutability of wild-type and polA host cells but did not alter either effect in a recA mutant. These R plasmids also increased the gamma radiation survival and gamma-induced mutability of wild-type host cells bud pMG15 also enhanced the level of spontaneous mutagenesis in wild-type host cells but not in a polA or recA mutant. These data suggested that a common plasmid gene product(s) may participate in various recA-dependent, error-prone deoxyribonucleic acid repair pathways of P. aeruginosa. The properties of a mutant R plasmid, pPL2, originally selected because it lacked enhanced ultraviolet-induced mutability, supported this conclusion.

Effect of bacteriophage C5 on ultraviolet light survival in Pseudomonas aeruginosa

Bacteriophage C5 of Pseudomonas aeruginosa is able to reactivate ultraviolet (u.v.)-irradiated phage E79 in coinfection experiments and decrease the u.v.-sensitivity of a host-cell reactivation deficient mutant. These properties suggest that phage C5 has a gene(s) which is involved in the repair of u.v.-damaged DNA. The isolation of two u.v.-sensitive mutants of C5 supports this hypothesis.

R plasmids which alter ultraviolet light-sensitivity and enhance ultraviolet light-induced mutability in Pseudomonas aeruginosa

R plasmids pMG1, R2, R931 and pMG15 increased the survival of Pseudomonas aeruginosa exposed to ultraviolet radiation (u.v.) in the wild type, and uvr and polA mutants but did not alter the u.v.-response of a recA mutant. The R plasmid RPL11 reduced u.v.-survival in the wild type, and uvr and polA mutants but did not alter the u.v.-response of a recA host. All the plasmids enhanced the level of spontaneous and u.v.-induced back mutation (Trp+) in a trpB1 strain. The effect of sublethal concentration of sodium arsenite following u.v.-irradiation was examined. It was concluded that in strains trpB1(pMG1) and trpB1(R931), u.v.-protection is determined by a recA+-dependent, arsenite-sensitive repair pathway, whereas in strains trpB1(R2) and trpB1(pMG15), u.v.-protection is determined by a recA+-dependent, arsenite-insensitive step in DNA repair.

Plasmid modification of radiation and chemical-mutagen sensitivity in Pseudomonas aeruginosa

The R factor pMG2 protects Pseudomonas aeruginosa against the lethal effects of ultraviolet (u.v.) and gamma irradiation, and methyl methanesulphonate and N-methyl-N'-nitro-N-nitrosoguanidine treatment. Enhanced survival occurs in strains of uvr+ rec+ (wild-type) genotype and a variety of uvr rec+ type mutants. No protection occurs in a rec A-type mutant. The plasmid also enhances u.v.-induced mutagenesis. These effects appear to be due to host-cell controlled plasmid-determined DNA repair function(s). Studies on P. aeruginosa strains deficient in DNA polymerase I (polyA) suggest that a plasmid-determined repair resynthesis function may be responsible for increased u.v.-survival and enhanced u.v.-mutability in pMG2-containing bacteria.

Fractures of the neck of the femur in childhood and adolescence

Twenty cases of fracture of the neck of the femur in children and adolescents below the age of 20 were reviewed. The most important single prognostic factor was the degree of displacement of the fracture at the time of injury. Undisplaced fractures, whether treated conservatively or by internal fixation, did well. Displaced fractures, however, always required internal fixation with thin pins after accurate correction of displacement. The various complications of this fracture in children are discussed. Acute necrosis of articular cartilage following this fracture in children is recorded for the first time in 2 cases.

Genetic analysis of radiation sensitive and chemical-mutagen sensitive mutants of Pseudomonas aeruginosa

Thirty-five mutants of Pseudomonas aeruginosa sensitive to methyl methanesulfonate (MMS) have been genetically characterized. They constitute ten separable groups as defined by transduction and conjugation. Three of the groups have been shown to be cotransducible with auxotrophic markers.