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P M Bennett

Publications and source records attributed to P M Bennett.

At least 145 records · Page 8Linked to original sources
PubMed1976

A molecular analysis of transductional marker rescue involving P-group plasmids in Pseudomonas aeruginosa.

The molecular properties of the P-group plasmids R26, R527 and R18-18- (a carbenicillin-sensitive derivative of R18) have been compared with those of RP1. R18-18 and RPI have a MW about 38 X 10(6) daltons, and R26 and R527 of 52 X 10(6) daltons (determined from contour lengths). All three plasmids have a bouyant density similar to that of RPI (1.719 g/cm3, 60% GN. From their molecular and phenotypic similarities, these plasmids probably represent two pairs of identical or closely similar elements. Resistant bacteria are not recovered following F116L-mediated transduction of R26 (or R527), and this correlates with the plasmids' larger size (phage genome=40 X 10(6) daltons). Fragments of R26 are, however, transduced and their resistance determinants may be "rescued" by recombination if the recipient harbours R1818. Such events are accompanied by an increase in the size of the recipient plasmid from 38 X 10(6) to 52 X 10(6) daltons following inheritance of the resistance determinants Sm Su Gm Hg, but not Cb. Thus, Sm Su Gm Hg are encoded in a DNA segment of MW about 14 X 10(6) daltons which apparently has no homologous region on R18-18. Since a piece of DNA of this MW also corresponds to the difference in size between R26 and R18-18, it is possible that the former is derived from an RPI-like element which has acquired these additional resistance determinants.

Carbenicillin↗
PubMed1976

Extrachromosomal deoxyribonucleic acid in wild-type and photosynthetically incompetent strains of Rhodopseudomonas spheroides.

Three covalently closed circular species of extrachromosomal deoxyribonucleic acid have been identified by electron microscopic analysis in strains of Rhodopseudomonas spheroides. The weights of these plasmids, as determined from contour length, are about 75 X 10(6), 66 X 10(6), and 28 X 10(6) daltons for both aerobically grown and photosynthetically grown R. spheroides strain 2.4.1 (NRS) and for the photosynthetically incompetent strain V-2 (obtained by N-methyl-N-nitro-N'nitrosoguanidine mutagenesis) and 74 X 10(6), 66 X 10(6) and 34 X 10(6) daltons for a second photosynthetically incompetent strain, SLS I (obtained by incubating strain 2.4.1 [NRS] in medium containing sodium lauryl sulfate). Buoyant densities uere found to be 1.717 g/cm3 (58% guanine plus cytosine) for the plasmids of 66 X 10(6), 28 X 10(6), and 34 X 10(6) daltons in weight and 1.724 g/cm3 (65% guanine plus cytosine) for those weighing about 75 X 10(6) daltons. Possible functions of these plasmids are discussed.

Aerobiosis↗
PubMed1976

Translocation of a discrete piece of deoxyribonucleic acid carrying an amp gene between replicons in Eschericha coli.

A number of well-characterized R plasmids (R1drd 19. K1.R100-1, R46, R55-1, R64-11, R388, and R751) will mobilize an integrated amp gene from the chromosome of Escherichia coli K-12. R391 will not act in this way. The process involves recombination, and in each case the mobilizing plasmid acquires an additional piece of deoxyribonucleic acid of molecular weight 4 X 10(6). Acquisition of this deoxyribonucleic acid may impair the transfer properties of the recombinant plasmid in some cases. The process will occur in a recA background.

Ampicillin↗
PubMed1976

Properties of pGC1, a lac plasmid orginating in Yersinia enterocolitica 842.

pGC1, a self-transmissible lac plasmid that originated in Yersinia enterocolitica 842, is described. This plasmid is freely transmissible between strains of Y. enterocolitica and from such strains to strains of Escherichia coli. The plasmid can also be transferref among G. coli strains and back to Y. enterocolitica, although at a greatly reduced frequency. pGC1 has a molecular weight of about 33.0 x 10(6), has a base composition of about 44 mol% guanine plus cytosine, and is fi-.

Conjugation, Genetic↗
PubMed1976

Acceptance and transfer of R-factor RP1 by members of the "herbicola" group of the genus Erwinia.

The R-factor RP1 was transferred by conjugation from Pseudomonas aeruginosa PAO12r(RPI) to various strains of Erwinia herbicola and to one strain of Erwinia stewartii. The exconjugate strains had minimum inhibitory concentration values for carbenicillin, kanamycin, neomycin, and tetracycline somewhat lower than the corresponding values for the pseudomonad RP1 donor strain. The biochemical characteristics of the exconjugant strains displayed minor variation in some instances from those of the corresponding R- strains. Sensitivity of the RP1+ strains to the RP1-specific bacteriophages PRD1 and PRR1 varied from an efficiency of plating [compared with P. aeruginosa PA067(RP1)] of 0 [E. herbicola Y46(RP1)] to 133 [E. herbicola Y190(RP1)] and 148 [E. stewartii SS104R(RP1)] for PRD1, and from 0 [E. herbicola Y46(RP1)] to 0.0002 [E. herbicola Y185(RP1)] and 18.4 [E. stewartii SS104R(RP1)] for PRR1. The phage-resistant strain E. herbicola Y46(RP1), would donate, by conjugation, the R-factor to E. herbicola Y46rifr, P, aeruginosa PAT900, or Escherichia coli UB1005 only at extremely low frequencies, if at all. Transformation of E. coli JC7620 by covalently closed circular DNA from E. herbicola Y46(RP1) gave and E. coli R+ strain exhibiting the expected antibiotic resistance pattern and having the ability to donate RP1 by conjugation. It is suggested (i) that some strains of E. herbicola RP1 either do not produce RP1 pili or produce defective pili, and (ii) that sensitivity to the bacteriophages PRD1 and PRR1 is not a suitable means of diagnosing the presence RP1 in E. herbicola strains.

Bacteriophages↗
PubMed1975

Reversible inactivation of the isocitrate dehydrogenase of Escherichia coli ML308 during growth on acetate.

During aerobic growth of Escherichia coli ML308 on acetate as sole carbon source, the apparent synthesis of isocitrate dehydrogenase was repressed relative to cultures on other carbon sources, such as glucose, which do not employ the glyoxylate bypass as an anaplerotic sequence. When cells were removed from an acetate medium, or when compounds were added which made the operation of the glyoxylate bypass unnecessary, the activity of isocitrate dehydrogenase rapidly increased 3- to 4-fold but fell again on restoration to an acetate medium. Changes in activity were rapid and, furthermore, could be demonstrated in the absence of protein synthesis. It is thus improbable that the mechanism involved degradation or de novo synthesis of the enzyme protein. Oxaloacetate and glyoxylate showed concerted inhibition of isocitrate dehydrogenase which could be relieved by dialysis. Because extracts of low enzyme activity, derived from acetate-metabolizing cells, could not be stimulated by dialysis or by addition of a wide range of metabolites, it is unlikely that low molecular weight, freely dissociable effectors were responsible for stimulation or inhibition of activity. Control of isocitrate dehydrogenase permitted the efficient utilization of acetate as sole source of carbon and energy but perserved the capacity of the cell to respond rapidly to an improvement in nutritional conditions. A limited survey showed that the mechanism is common but not universal among strains of E. coli and occurs in at least one strain each of Klebsiella aerogenes, Salmonella typhimurium and Serratia marcescens.

Acetates↗
PubMed1973

Messenger ribonucleic acid synthesis and degradation in Escherichia coli during inhibition of translation.

Various aspects of the coupling between the movement of ribosomes along messenger ribonucleic acids (mRNA) and the synthesis and degradation of mRNA have been investigated. Decreasing the rate of movement of ribosomes along an mRNA does not affect the rate of movement of some, and possibly most, of the RNA polymerases transcribing the gene coding for that mRNA. Inhibiting translation with antibiotics such as chloramphenicol, tetracycline, or fusidic acid protects extant mRNA from degradation, presumably by immobilizing ribosomes, whereas puromycin exposes mRNA to more rapid degradation than normal. The promoter distal (3') portion of mRNA, synthesized after ribosomes have been immobilized by chloramphenicol on the promoter proximal (5') portion of the mRNA, is subsequently degraded.

Carbon Radioisotopes↗