Plasmid DNA in Streptococcus cremoris Wg2: Influence of pH on Selection in Chemostats of a Variant Lacking a Protease Plasmid

Cleared lysates of a proteolytic (Prt) strain and a naturally occurring non-proteolytic (Prt) variant of Streptococcus cremoris Wg2 contain equal amounts of covalently closed circular plasmid DNA. An analysis of this plasmid DNA by agarose gel electrophoresis revealed the presence of at least five different plasmid species in the Prt strain and only three plasmid species in the Prt variant. Curing studies with acriflavine indicated that a 16-megadalton plasmid determined proteolytic activity in the Prt strain. In energy-limited chemostats inoculated with both strains it was observed that the Prt strain was replaced by the Prt variant. This effect was most apparent when the pH of the culture was fixed at a value above 6.3. No selection for the Prt variant was observed at pH 5.9. Since the two types of organisms contain equal amounts of plasmid DNA, it was concluded that the energy gain of the Prt variants at pH values above 6.0 probably has to be found in protein synthesis rather than in plasmid DNA synthesis.

Inverse temperature dependent lifetimes of transient S(N)2 ion-dipole complexes

The association and collisional stabilization of the S(N)2 entrance channel complex [Cl(-)...CH3Cl]* is studied in a low-temperature radiofrequency ion trap. The temperature dependence of the ternary rate coefficient is measured and a much stronger inverse temperature dependence than expected from a simple statistical calculation is found. From these data the lifetime of the transient S(N)2 complex has been derived as a function of temperature. It is suggested that the inverse temperature dependent rates of nonsymmetric S(N)2 reactions are related to the observed inverse temperature dependence of the transient ion-dipole complexes.

Nonstandard behavior of a negative ion reaction at very low temperatures

We have studied the negative ion reaction NH2-+H_{2}-->NH_{3}+H- in the temperature range from 300 to 8 K. We observe a strongly suppressed probability for proton transfer at room temperature. With decreasing temperature, this probability increases, in accordance with a longer lifetime of an intermediate anion-neutral complex. At low temperatures, a maximum in the reaction rate coefficient is observed that suggests the presence of a very small barrier at long range or a quantum mechanical resonance feature.

[Stereotactic Mammotome breast biopsy: routine clinical experience and correlation with BI-RADS--classification and histopathology]

BACKGROUND

Stereotactic breast biopsy using the Mammotome system allows minimal invasive tissue sampling of suspicious lesions of the breast cancer, e.g. clustered microcalcifications BI-RADS type 3 and 4, and has widely replaced open surgical biopsies. The aim of this retrospective study was to review the results of these biopsies in regard of technical feasibility and complications as well as to correlate initial BI-RADS assessment with histopathology.

METHODS

One hundred thirty-five vacuum-assisted breast biopsies in 124 patients were evaluated. Before biopsy, the mammograms were classified according to the Breast Imaging Reporting and Data System (BI-RADS). All mammograms were reviewed with knowledge of the final histologic diagnosis. Patients with benign diagnoses underwent mammographic follow-up. Excisional biopsy was recommended for diagnoses of in-situ or invasive carcinoma.

RESULTS

No serious complications of the biopsies were observed. Histopathology revealed 105 (78%) benign lesions. Benign lesions were classified as BI-RADS 3 in 49 (36%) and as suspicious (BI-RADS 4) in 56 (41%). Thirty lesions (22%) were malignant, of which 26 (87%) were classified BI-RADS 4 or 5. The frequency of malignancy in BI-RADS 4 and 5 was 19 of 75 (25%) and 7 of 7 (100%), respectively. Of the 53 BI-RADS 3 lesions, 4 (8%) were malignant.

CONCLUSIONS

Mammotome biopsy was shown to be a safe and well-tolerated technique for the work-up of mammographic lesions. The frequency of malignant histopathologic findings in BI-RADS 3 lesions was higher than expected, reflecting the difficulties in the mammographic differentiation of benign and malignant clustered microcalcifications.

Photodetachment of cold OH- in a multipole ion trap

The absolute photodetachment cross section of OH- anions at a rotational and translational temperature of 170 K is determined by measuring the detachment-induced decay rate of the anions in a multipole radio-frequency ion trap. In comparison with previous results, the obtained cross section shows the importance of the initial rotational-state distribution. Using a tomography scan of the photodetachment laser through the trapped ion cloud, the derived cross section is model-independent and thus features a small systematic uncertainty. The tomography also yields the column density of the OH- anions in the 22-pole ion trap in good agreement with the expected trapping potential of a large field free region bound by steep potential walls.

Quantitative high resolution transmission electron microscopy of nanostructured semiconductors

Peak-finding procedures and the geometric phase method of quantitative high resolution electron microscopy (qHRTEM) were applied to determine the local strain and the chemical composition of nanostructured semiconductor materials. The growth of the structures investigated was induced by minimization of strain energy. The analysis of strain distribution is necessary for the understanding of the self-organized formation of nanostructures. The possibilities and limitations of the methods are discussed in detail by analysing HRTEM images of (Si,Ge) islands and of a double layer of stacked quantum dots of (In,Ga)As and Ga(Sb,As).