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Biomedical subjects

J B Armstrong

Publications and source records attributed to J B Armstrong.

66 records · Page 4Linked to original sources
PubMed1973

Osmotic reversal of temperature sensitivity in Escherichia coli.

Forty temperature-sensitive mutants, unable to grow on tryptone or nutrient agar at 42 C, were isolated from Escherichia coli K-12. When 0.5% NaCl was added to the medium, 32 grew at the nonpermissive temperature. Several were tested with different amounts of NaCl added to tryptone broth; all grew best when the osmolality of the medium was between 400 and 1,000 milliosmolal. One of the mutants was studied in more detail. Sucrose, inositol, KCl, and MgCl(2), as well as NaCl, permitted growth at 42 C. Glycerol, however, had no effect. When shifted from 30 to 42 C without osmotic protection, the mutant stopped growing but did not lyse, die, or leak significant amounts of intracellular material. In a similar shift experiment, a second mutant leaked all of its trichloroacetic acid-soluble pools into the medium. The majority of the mutants were hypersensitive to certain antibiotics, indicating possible cell envelope defects.

Amino Acids↗
PubMed1969

Location of genes for motility and chemotaxis on the Escherichia coli genetic map.

In Escherichia coli, the following genes are involved in motility and chemotaxis. The H gene is the structural gene for flagellin. Mutation in the mot gene results in paralysis of the flagella, and mutation in the fla genes leads to an absence of flagella. The cheA, cheB, and cheC genes are required for chemotaxis. The chromosomal location of these genes has now been determined. The majority are clustered in a small region around uvrC, between his and aroD, in the order his-cheC-H-uvrC-mot-cheA-cheB-aroD. The fla genes are located in the same region, and also between trp and gal. The results indicate that many of the genes are homologous to those which have been studied in Salmonella typhimurium.

Cell Biology↗
PubMed1967

Nonchemotactic mutants of Escherichia coli.

We have isolated 40 mutants of Escherichia coli which are nonchemotactic as judged by their failure to swarm on semisolid tryptone plates or to make bands in capillary tubes containing tryptone broth. All the mutants have normal flagella, a fact shown by their shape and reaction with antiflagella serum. All are fully motile under the microscope and all are sensitive to the phage chi. Unlike its parent, one of the mutants, studied in greater detail, failed to show chemotaxis toward oxygen, glucose, serine, threonine, or aspartic acid. The failure to exhibit chemotaxis does not result from a failure to use the chemicals. The swimming of this mutant was shown to be random. The growth rate was normal under several conditions, and the growth requirements were unchanged.

Aspartic Acid↗
PubMedDate not supplied

Effects of fenitrothion and carbaryl on Xenopus laevis development.

When Xenopus laevis embryos were treated with fenitrothion, a substantial proportion failed to survive to hatching only when the concentration approached saturation. However, after exposure to 10 ppm of fenitrothion, most were abnormal and did not survive past feeding stage. Different embryonic stages were not equally sensitive to fenitrothion and the greatest sensitivity was observed at gastrulation. The most common visible abnormalities were altered body shape, including microcephaly, and edema. Internally, abnormalities of the heart, spinal cord and notochord were common. Though carbaryl was toxic at somewhat lower concentrations, carbaryl-induced abnormalities were less severe. In particular, cardiac malformations were less extreme. Recently hatched tadpoles were less sensitive to carbaryl than were the embryos, but were more sensitive to fenitrothion. However, with both compounds, the effects were seen only at concentrations higher than would normally be expected in the environment after spraying.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

Ectopic expression of a genomic fragment containing a homeobox causes neural defects in the axolotl.

An axolotl (Ambystoma mexicanum) genomic fragment containing the Ahox1 homeobox was placed under the control of the mouse hsp68 promoter, which seems to function constitutively in the axolotl. The resulting construct was injected into fertilized axolotl eggs to see if it would perturb development. Of the injected embryos, 20% showed severe reduction of the anterior neural plate. Later in development, these embryos had small heads, no eyes, and appeared to lack the normal regionalization of the brain. An additional 35% of the embryos were less severely affected, but had reduced or missing eyes. Control embryos, including ones injected with a construct missing the DNA recognition helix of the homeobox, developed normally.

Ambystoma↗