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Biomedical subjects

R J Rowbury

Publications and source records attributed to R J Rowbury.

At least 73 records · Page 4Linked to original sources
PubMed1976

On the mode of action of 5-diazouracil on bacterial cell division.

Cell division by strains of Escherichia coli and Salmonella typhimurium is inhibited by 5-diazouracil (5-DU). Division recovers in the presence of the inhibitor after a period which is temperature-dependent. Recovery is probably due to breakdown of 5-DU and the rate of this breakdown is apparently increased at alkaline pH. Growth with 5-DU caused only a slight reduction in the rate of murein synthesis and no alteration in the properties or composition of membranes of S. typhimurium. The agent caused chaining in Streptococcus fecalis and inhibition of the penicillin-induced lysis of S. typhimurium. These effects may have been due to direct inhibition of lysin activity but an indirect effect seems more likely. The most marked effect of 5-DU on S. typhimurium was to cause a transient inhibition of DNA synthesis. Since 5-DU did not stop uncoupled cell division (i.e. division occurring independently of DNA replication) and since lon- strains were more sensitive to 5-DU than lon+ strains, it was concluded that 5-DU acts on cell division via an inhibitory effect on DNA replication.

Azo Compounds↗
PubMed1976

The formation of a dissociable plasmid cointegrate from the Flac factor and the resident plasmid of Salmonella typhimurium LT2.

The Flac factor showed unstable maintenance in Salmonella typhimurium dnaC MP10LT2. The properties of a more stable lac+ derivate (SD-1) are described. SD-1 was ts and carried the fi+ property and the ability to transfer the lac+ character. It contained a large plasmid of molecular weight about 129 X 10(6) DALTONS. The properties of SD-1 and its derivatives suggested that the large plasmid was a cointegate of Flac and the MP10lt2 plasmid. Lac+ transfer was efficient from SD-1 to M799 MP10LT2 and one lac+ exconjugant contained the intact cointegrate. The cointegrate was not successfully transferred to strains lacking MP10LT2. It dissociated into apparently unaltered Flac and MP10LT2 plasmids, but the deletion of small parts of one or both plasmids during cointegrate formation could not be ruled out. Cointegrate dissociation was more marked in M799 than in SD-1 especially during growth in glucose-Casamino acids minimal medium. In the presence of R1drd19, the cointegrate (like the MP10LT2 plasmid) was stable maintained in the dnaC strain; maintenance of Flac was, however, unstable. It seems likely that replication of the cointegrate was controlled by the MP10LT2 plasmid constitutent.

Conjugation, Genetic↗
PubMed1975

Mode of growth and division of Salmonella typhimurium.

A temperature-sensitive strain (HD 20) of Salmonella typhimurium is described. At restrictive temperature this strain shows an envelope alteration and a defect in division associated with an increase in cell diameter. On a shift to 42 degrees C there is residual division for ca. 30 min and then no further increase in cell number. In minimal medium (MM) at 42 degrees C cell diameter remains unchanged for about one mass doubling and then increases. From measurements of cell elongation, it is concluded that such increases in diameter occur because cell volume increases exponentially at 42 degrees C but increases in the rate of elongation occur for only a short period and then elongation rate becomes constant. This conclusion is supported by the observation that HD 20 cells show no increase in diameter at 42 degrees C when cultured in media supplemented with sucrose and Mg++; normal increases in elongation rate occur in such media. A model which fits the experimental data has been constructed. This model has two main features namely (1) the elongation of individual cells is linear with the rate of elongation doubling close to division and (2) such doublings in elongation rate are linked to division such that division cannot occur if elongation rate has not doubled shortly before. In the mutant it is proposed that only a few doublings in elongation rate occur at 42 degrees C and these are responsible for the residual division. The model fits the data for cultures shifted to 42 degrees C in MM or in yeast extract casamino acids MM (YE Cas MM) and for cultures shifted to 42 degrees C and shifted up from MM to YE Cas MM. The observations on these medium shifted cultures suggest that the activity of growth zones responsible for elongation is medium dependent.

Cell Division↗