Progress in high-resolution autoradiography

Evidence for diffuse growth of the cylindrical portion of the Escherichia coli murein sacculus

High-resolution autoradiography of thin sections of Escherichia coli cells whose murein was pulse-labeled with [3H]diaminopimelic acid after a period of diaminopimelic acid deprivation indicated that elongation of the murein sacculus occurs by a multisite (diffuse) process. Upon chasing, radioactivity in polar murein was stable, whereas radioactivity in cylindrical murein was reduced, indicating that diffuse intercalation of new murein occurred during cell elongation. Elongation and septation were shown to be overlapping processes.

Bacillus megaterium sporal peptidoglycan synthesis studied by high-resolution autoradiography

Cells of a Dap- Lys- mutant strain of Bacillus megaterium were pulse labeled with [3H]diaminopimelic acid at different times of growth and sporulation. They were processed for radioactivity measurements and high-resolution autoradiography either just after the pulse or after a chase in a nonradioactive medium until refractile forespores started to appear at time (t)4,5. In the pulse-labeled cells, autoradiographs and radioactivity measurements showed that the radioactivity incorporated during a pulse decreased abruptly after t0 and stayed at a low level until t5, although the forespore wall and cortex were formed between t4 and t5. In the pulse-chased bacteria, the acid-insoluble radioactivity, as well as the number of silver grains on autoradiographs, increased during the chase in cells labeled at t1 to t2, whereas it decreased in those labeled before t0. Furthermore, analysis of silver grain distribution showed that, in stage IV bacteria, grains were distributed at the outside of the forespore, mostly on the sporangium cell wall, when pulse-labeling occurred before or at t0; they were located along the cortex and in the forespore cytoplasm when labeling was made at t1 or t2. These facts show that [3H]diaminopimelic acid necessary for spore envelope synthesis was incorporated before their morphological appearance. Free or small diaminopimelic acid precursors entered the sporangium between t1 and t2. The appearance of silver grains in the forespore cytoplasm suggests that the forespore is implicated in sporal peptidoglycan synthesis.

Uracil incorporation in the forespore and the mother cell during spore development in Bacillus subtilis. Autoradiographic electron microscopic study

The transcriptional activity of the two genomes of the sporangium during spore formation was determined by pulse-labeling bacteria with 3H-uracil at different times of sporulation and preparing them for high resolution autoradiography. The quantitative analysis of autoradiographs shows that uracile incorporation in the whole sporangium decreases considerably between stages II and IV. However, the variations of the transcriptional activity are not identical in the mother cell and in the forespore. The one of the mother cell decreases rapidly between stages II and III and then remains stable until the end of stage IV, whereas that of the forespore which is low at stage II increases as the forespore grows ovoid and then quickly diminishes. It is very weak at the beginning of stage IV and negligible at the end of this stage. Pulse-chase experiments made in the presence of rifampine indicate that about 30% of the uracile incorporated is located in stable RNA. This value is found at any stage of sporulation in both cellular compartments whatever their rate of uracile incorporation. A relationship can be made between the nuclear shape and the activity of the genetic material. This confirms observations made by several authors in other bacterial species and other physiological conditions that the condensed shape corresponds to a state of low transcriptional activity whereas the more irregular and dispersed shape corresponds to a state of high activity.

Study of cell wall growth in Bacillus megaterium by high-resolution autoradiography

Growth of the cell wall of Bacillus megaterium was studied by pulse-labeling the cell wall of a DAP- Lys- mutant for a very short time with tritium-labeled diaminopimelic acid. The distribution of radioactivity along the cell wall was examined by high-resolution autoradiography on isolated cell walls and thin sections of bacteria. The results indicate that cell wall elongation occurs by diffuse intercalation of newly synthesized murein into the expanding cell wall during exponential growth, as well as during germination, and that the only zone of highly localized diaminopimelic acid incorporation is found at the cross wall during its synthesis. This zone contains about 30% of the radioactivity incorporated into the cell wall. Analysis of autoradiographs of thin sections of bacteria shows that the total radioactivity incorporated per bacterium doubles during the life cycle. This doubling occurs in the cylindrical part of the cell wall but not in the polar caps. This seems to indicate that elongation of the bacterium is not constant during the life cycle but increases with the length of the cell.

Quantitative radioautography of sugar transport in intestinal biopsies from normal humans and a patient with glucose-galactose malabsorption

Both galactose accumulation and phlorizin binding by columnar epithelial cells have been investigated in vitro with a recently developed technique for high-resolution, plastic-section radioautography which is particularly suited to small quantities of biopsy tissue. Grain density analysis of the radioautographs provides definitive support for the view that the cellular mechanisms underlying glucose-galactose absorption in laboratory animals are fully applicable to the small intestine of man. Even the number of sugar carriers at the microvillar membrane appears similar and the major quantitative difference, lower affinity for phlorizin in man, correlates with the finding that phlorizin is also a less potent inhibitor of uphill, galactose transport at the microvilli. In addition, radioautographs of biopsies taken 2 yr apart from a patient with glucose-galactose malabsorption provide evidence that the cellular defect in this inborn error of transport is a persistent reduction in the number of functioning sugar carriers at the microvillar membrane.

Synthesis of ribonucleic acid and protein in plasmid-containing minicells of Escherichia coli K-12

Unlike the deoxyribonucleic acid (DNA)-deficient minicells produced by F(-) parents, minicells produced by plasmid-containing strains contain significant amounts of plasmid DNA. We examined the ability of plasmid-containing minicells to synthesize ribonucleic acid (RNA) and protein. In vivo, minicells produced by F(-) parents are unable to incorporate radioactive precursors into acid-insoluble RNA or protein, whereas minicells produced by F', R(+), or Col(+) parents are capable of such synthesis. Using a variety of approaches, including polyacrylamide gel analysis of the RNA species produced and electron microscope autoradiography, we demonstrated that the synthesis observed in minicell preparations is a property of the plasmid-containing minicells and not a result of the few cells (approximately 1 per 10(6) minicells) contaminating the preparations. That the observed synthesis is of biological importance is suggested by the ability of plasmid-containing minicells to yield viable phage upon infection with T4.

Uranium localization on hydroxyapatite by analysis of fission fragment tracks

The distribution of enriched uranium on individual hydroxyapatite crystals after an exchange reaction has been investigated by means of thermal neutron irradiation followed by electron microscopic analysis of fission fragment tracks in plastic support films. One uranyl ion for every two to three surface calcium ions became associated with the mineral but in a nonuniform distribution that strongly favors crystal end regions.