Behavior ofPseudomonas fluorescens within the hydrodynamic boundary layers of surface microenvironments

Phase, darkfield, and computer-enhanced microscopy were used to observe the surface microenvironment of flow cells during bacterial colonization. Microbial behavior was consistent with the assumptions used previously to derive surface colonization kinetics and to calculate surface growth and attachment rates from cell number and distribution. Surface microcolonies consisted of closely packed cells. Each colony contained 2ⁿ cells, where n is the number of cell divisions following attachment. Initially, cells were freely motile while attached, performing circular looping movements within the plane of the solid-liquid interface. Subsequently, cells attached apically, maintained a fixed position on the surface, and rotated. This type of attachment was reversible and did not necessarily lead to the formation of microcolonies. Cells became irreversibly attached by progressing from apical to longitudinal attachment. Longitudinally attached cells increased in length, then divided, separated, moved apart laterally, and slid next to one another. This resulted in tight cell packing and permitted simultaneous growth and adherence. After approximately 4 generations, individual cells emigrated from developing microcolonies to recolonize the surface at new locations. Surface colonization byPseudomonas fluorescens can thus be subdivided into the following sequential colonization phases: motile attachment phase, reversible attachment phase, irreversible attachment phase, growth phase, and recolonization phase.     

The relative biological effectiveness of 670 MeV/A neon as a function of depth in water for a tissue model

Linear energy transfer (LET infinity) spectra of identified charge fragments and primaries, produced by nuclear interactions of 670 MeV/A neon in water, were measured along the unmodulated Bragg curve of the neon beam. The relative biological effectiveness (RBE) values for spermatogonial cell killing, as reported on the basis of weight loss assay of mouse testes irradiated with beams of approximately constant single LET infinity, were summed over the particle LET infinity spectra to obtain an effective RBE for each charged-particle species, as a function of water absorber thickness. The resultant values of effective RBE were combined to obtain an effective RBE for the mixed radiation field. The RBE calculated in this way was compared with experimental RBEs obtained for spermatogonial cell killing in the mixed radiation field produced by neon ions traversing a thick water absorber. Discrepancies of 10-40% were observed between the calculated RBE and the RBE measured in the mixed radiation field. Part of this discrepancy can be attributed to undetected low-Z fragments, whose contribution is not included in the calculation, leading to an overestimated value for the calculated RBE. On the other hand, calculated values 10% greater than the measured RBE are explained as track structure effects due to the higher radial ionization density near neon tracks relative to the ionization density near the silicon tracks used to fit the RBE vs LET infinity data.     

Immunological heterogeneity of rat apolipoprotein B epitope expression. A study using monoclonal antibodies to rat apolipoprotein B

Epitope expression of rat apolipoprotein B on lipoproteins was investigated with the help of six monoclonal antibodies produced from mice. Through a variety of techniques, which include cotitrations, ELISAs and quantitative immunoadsorption precipitation, we concluded that the six monoclonal antibodies recognize five different epitopes. LRB 110 and LRB 260 recognize epitopes that may be overlapping. LRB 240 and LRB 250 recognize epitopes that are preferentially expressed in triacylglycerol-rich particles. LRB 220 recognizes an epitope that is expressed by all apolipoprotein-B-containing lipoproteins. We have also determined that apolipoprotein B epitope expression in rat lipoproteins is very similar to its human counterpart. Both rat and human apolipoprotein B epitope expression on lipoproteins showed heterogeneities even in homologous lipoprotein preparations. We concluded that a variety of techniques are necessary to fully characterize monoclonal antibodies to apolipoproteins. The possible implications of epitope expression in pathophysiology are also discussed.     

A new approach to chromosome doubling for haploid rice plants

Summary Rice nodal segments from three flowering haploids were excised and treated for different lengths of time with 0.3% or 0.4% colchicine (dissolved in 2% DMSO) in an attempt to induce fertile seeds. A combination of higher colchicine concentration and longer hours of treatment reduced the survival rate of treated segments, but more fertile plants were transformed. Pooled data showed that of the 842 segments used, 42.2% survived the treatment and sprouted, but only 31.9% were successfully established and grown to maturity. Among the 269 mature plants, 29,4% produced fertile seeds (panicles) with an average of 146.2 seeds per diploidized plant.     

Radiolysis of DNA in aqueous solution in the presence of a scavenger: A kinetic model based on a nonhomogeneous reaction of OH radicals with DNA molecules of spherical or cylindrical shape

Summary Two expressions are given for the survival dose of DNA exposed to high-energy radiation in aqueous solution in the presence of a scavenger. They are derived from a model where a diffusion controlled reaction of OH radicals occurs on the surface of the DNA macromolecules in competition with scavenging in the bulk of the solution. The DNA molecules are approximated either by spheres or by cylinders. The model based on molecules of spherical shape corresponds closely to that developed by van Rijn et al. [20]. Expressions obtained from the cylindrical model are used to account for the dependence on the scavenger concentration of some experimentally measured quantities, namely the survival dose and theG value for single-strand breaks upon Co -irradiation ofX 174 DNA and polyadenylic acid, respectively.In memoriam Prof. Dr. O.E. Polansky     

Determination of desmosine, isodesmosine, and other amino acids by liquid chromatography with electrochemical detection following precolumn derivatization with naphthalenedialdehyde/cyanide

Naphthalenedialdehyde (NDA) in the presence of cyanide (CN) reacts with primary amines to produce fluorescent cyano[f]benzoisoindole (CBI) derivatives. These derivatives have been shown to be substantially more stable than the corresponding o-phthalaldehyde derivatives. However, one drawback of this method is that compounds derivatized at more than one site exhibit quenching, precluding the use of fluorescence detection. The CBI derivatives have been found to be electroactive and are oxidized at a modest oxidation potential (+750 mV). Electrochemical detection is especially useful for the analysis of compounds containing more than one primary amine site because the response is not attenuated as it is in fluorescence detection. Desmosine and isodesmosine were of particular interest because of their importance in elastic fiber and the lack of highly sensitive HPLC methods for the determination of these compounds. Both of these compounds react with NDA/CN to produce electrochemically active derivatives. The combination of derivatization with NDA/CN and electrochemical detection was found to be linear over three orders of magnitude. Detection limits for CBI-lysine and CBI-desmosine were 100 fmol at a S/N of 2. Amino acids in elastin were quantitated using this method. The results correlate well with what has been reported previously in the literature. A significant advantage of the use of liquid chromatography with electrochemical detection with precolumn derivatization with NDA/CN for the analysis of desmosine and isodesmosine is that they can be separated and quantitated individually using this method. In addition, the unique voltammetry of multiderivatized CBI-amino acids can be used to verify peak purity.     

Evidence for a novel growth factor in Xenopus oocytes

Xenopus oocytes contain a novel growth factor, as determined by its effect on the anchorage-dependent and -independent growth of various rat cells and on a Xenopus cell line; it is destroyed by trypsin, acidification (pH 2.0), heating (100 degrees C, 3 min), 8 M urea but not by dithiothreitol. Gel filtration of this activity in nondissociating conditions suggests the existence of aggregates and the presence of a very high (approximately 2000 Kd) and a much lower (approximately 30 Kd) form.