Study of the amniotic fluid from smokers and non-smokers in the Ames test

Amniotic fluid from smokers and non-smokers was tested by the Salmonella/mammalian microsome test. Concentrated amniotic fluid from heavy smokers at term showed an increase in the number of revertants with increasing exposure to tar. However, some of the non-smokers had a higher number of revertants than the smokers. No significant differences were found between second-trimester samples from smokers and non-smokers, but the limited volumes available at this stage of pregnancy may be a source of error.     

Effect of chlorine dioxide on selected membrane functions of Escherichia coli

The mode of action of chlorine dioxide on Escherichia coli was assessed by studying outer membrane permeability to macromolecules and potassium, and observing effects on respiration. The results indicate that gross cellular damage involving significant leakage of intracellular macromolecules does not occur. There was a substantial efflux of potassium, however, and respiration was inhibited even at sublethal doses. It was concluded that the inhibition of respiration, which could be due to the damage to the cell envelope, was not the primary lethal event. Observations of the efflux of K⁺ strongly implicate the loss of permeability control as the primary lethal event at the physiological level, with nonspecific oxidative damage to the outer membrane leading to the destruction of the trans-membrane ionic gradient.     

Orientation constraints in diffusion-limited macromolecular association. The role of surface diffusion as a rate-enhancing mechanism.

Ligand association to a reactive site on a macromolecular surface could be very slow if the site is small. The effective capture radius of the reactive site can be significantly increased if the ligand can bind weakly to the nonspecific surface around the site and then slide in a two-dimensional diffusion along the surface. In this model, the diffusion along the surface has to be properly coupled with the free diffusion in solution and the effective bimolecular association rate constant to the reactive site can be calculated as a function of the nonspecific affinity. This is carried out both for a plane and spherical surface, modeling the association to a membrane receptor or to the catalytic site on an enzyme. The result of these calculations can be used to assign reasonable values to the parameters in the quasichemical approximation of K. Solc and W. H. Stockmayer (1973, Int. J. Chem. Kinet., 5:733-752). In this way a simple analytical expression can be derived for the diffusion-limited association rate constant of two asymmetrically reactive molecules, with or without surface diffusion contributing.     

Retinol and retinyl esters in parenchymal and nonparenchymal rat liver cell fractions after long-term administration of ethanol

Chronic ethanol consumption reduces the liver retinoid store in man and rat. We have studied the effect of ethanol on some aspects of retinoid metabolism in parenchymal and nonparenchymal liver cells. Rats fed 36% of total energy intake as ethanol for 5-6 weeks had the liver retinoid concentration reduced to about one-third, as compared to pair-fed controls. The reduction in liver retinoid affected both the parenchymal and the nonparenchymal cell fractions. Plasma retinol level was normal. Liver uptake of injected chylomicron [3H]retinyl ester was similar in the experimental and control group. The transport of retinoid from the parenchymal to the nonparenchymal cells was not found to be significantly retarded in the ethanol-fed rats. Despite the reduction in total retinoid level in liver, the concentrations of unesterified retinol and retinyl oleate were increased in the ethanol fed rats. Hepatic retinol esterification was not significantly affected in the ethanol-fed rats. Since our study has demonstrated that liver uptake of chylomicron retinyl ester is not impaired in the ethanol-fed rat, we suggest that liver retinoid metabolism may be increased.     

Susceptibility of chemostat-grown Yersinia enterocolitica and Klebsiella pneumoniae to chlorine dioxide

The resistance of bacteria to antimicrobial agents could be influenced by growth environment. The susceptibility of two enteric bacteria, Yersinia enterocolitica and Klebsiella pneumoniae, to chlorine dioxide was investigated. These organisms were grown in a defined medium in a chemostat and the influence of growth rate, temperature, and cell density on the susceptibility was studied. All inactivation experiments were conducted with a dose of 0.25 mg of chlorine dioxide per liter in phosphate-buffered saline at pH 7.0 and 23 degrees C. The results indicated that populations grown under conditions that more closely approximate natural aquatic environments, e.g., low temperatures and growth at submaximal rates caused by nutrient limitation, were most resistant. The conclusion from this study is that antecedent growth conditions have a profound effect on the susceptibility of bacteria to disinfectants, and it is more appropriate to use the chemostat-grown bacteria as test organisms to evaluate the efficacy of a certain disinfectant.     

Evaluation of a fluorescent antibody technique for the rapid enumeration of Bacteroides fragilis group of organisms in water

The Bacteroides fragilis group has been evaluated as a prospective rapid indicator of faecal contamination of water. Fluorescent antibody (FA) stained B. fragilis group bacteria were enumerated microscopically and compared with faecal coliform or Escherichia coli counts as indicators of faecal contamination. Environmental samples included surface waters (raw drinking water and known contaminated water). Laboratory disinfection experiments with ozone, chlorine and u. v. radiation were also performed. Bacteroides FA counts specifically detected recent human faecal contamination in field samples in 2–3 h. Samples with a high content of particulates or debris limited the sensitivity to about 10 FA counts/ml. Viable counts showed that the sensitivity to all three disinfection agents was essentially the same for Bacteroides and E. coli. Fluorescent antibody counts of Bacteroides , conversely, were not altered by any of the agents. Therefore, the Bacteroides FA method is not recommended for routine monitoring but may be useful for cases where extensive human faecal contamination is suspected (e.g. pipeline rupture or pollution of recreational water) and where rapid remedial action must be taken to protect the public health.     

Coordination of flagella on filamentous cells of Escherichia coli.

Video techniques were used to study the coordination of different flagella on single filamentous cells of Escherichia coli. Filamentous, nonseptate cells were produced by introducing a cell division mutation into a strain that was polyhook but otherwise wild type for chemotaxis. Markers for its flagellar motors (ordinary polyhook cells that had been fixed with glutaraldehyde) were attached with antihook antibodies. The markers were driven alternately clockwise and counterclockwise, at angular velocities comparable to those observed when wild-type cells are tethered to glass. The directions of rotation of different markers on the same cell were not correlated; reversals of the flagellar motors occurred asynchronously. The bias of the motors (the fraction of time spent spinning counterclockwise) changed with time. Variations in bias were correlated, provided that the motors were within a few micrometers of one another. Thus, although the directions of rotation of flagellar motors are not controlled by a common intracellular signal, their biases are. This signal appears to have a limited range.     

Homologous and nonhomologous recombination in monkey cells.

Though recombinational events are important for the proper functioning of most cells, little is known about the frequency and mechanisms of recombination in mammalian cells. We have used simian virus 40 (SV40)-pBR322 hybrid plasmids constructed in vitro as substrates to detect and quantitate intramolecular homologous and nonhomologous recombination events in cultured monkey cells. Excision of wild-type or defective SV40 DNAs by recombination from these plasmids was scored by the viral plaque assay, in either the absence or the presence of DNA from a temperature-sensitive helper virus. Several independent products of homologous and nonhomologous recombination have been isolated and characterized at the DNA sequence level. We find that neither DNA replication of the recombination substrate nor SV40 large T antigen is essential for either homologous or nonhomologous recombination involving viral or pBR322 sequences.     

Electronmicroscopic Observations on the Degradation of Cellulose Fibres by Cellvibrio fulvus and Sporocytophaga myxococcoides

S ummary : Cellvibrio fulvus and Sporocytophaga myxococcoides were grown on different types of cellulose fibres and the degradation was followed by means of light and electron microscopy. The very compact fibres prepared from cotton were degraded slowly by C. fulvus. The bacteria penetrated into the lumen of the fibres, accumulated there in large numbers, and degraded the fibres from within. Sporocytophaga myxococcoides attacked fibres both from the outside and from within by making close contact with the cellulose. Lignin free pulp fibres, which have a very open structure, were rapidly degraded by both kinds of bacteria. Cellvibrio fulvus also degraded these fibres from within. It is concluded that structure of the fibre greatly influences the rate at which different kinds of cellulolytio bacteria decompose cellulose.