Interchromosomal recombination in the extremely radioresistant bacterium Deinococcus radiodurans.

Deinococcus radiodurans and other members of the genus Deinococcus are remarkable for their extreme resistance to ionizing radiation and many other agents that damage DNA. We have recently shown that recombinational processes participate in interplasmidic repair following in vivo irradiation. We now present direct studies on interchromosomal recombination among chromosomes irradiated in vivo during stationary phase (four chromosomes per cell). Following an exposure to 1.75 Mrad (the dose required to achieve a survival of 37%, which degrades the cells' four chromosomes into about 500 fragments), we determined that there may be as many as 175 crossovers per chromosome (700 crossovers per nucleoid) undergoing repair. In addition, these studies suggest that many of the crossovers occurring during repair are nonreciprocal.     

Quantitative analysis of biofilm thickness variability

The thickness variability of biofilms of Pseudomonas aeruginosa, Klebsiella pneumoniae, and the binary population combination of these two species was quantified. The experimental method involved cryoembedding biofilms with a commercial tissue embedding agent, sectioning, and applying image analysis to construct thickness profiles along linear transects (up to 1 cm in length) across the substratum. Biofilms embedded and sectioned by this method were locally as thin as a single cell attached to the surface (<5 mum) and as thick as 1000 mum. Week-old biofilms of three different species compositions displayed distinct structural features as indicated by their mean thicknesses and by a roughness coefficient. Monopopulation biofilms of P. aeruginosa (29 mum mean thickness) or K. pneumoniae (100 mum mean thickness) were thinner than the binary population biofilm (400 mum mean thickness). A roughness coefficient developed in this investigation corroborated the qualitative visual characterization of P. aeruginosa biofilms as relatively uniformly thick (mean roughness coefficient 0.15), K. pneumoniae biofilms as patchy (mean roughness coefficient 1.14), and the binary population biofilm as intermediate (mean roughness coefficient 0.26). Whereas P. aeruginosa and binary population biofilms covered the substratum completely, significant areas of essentially bare substratum were apparent in K. pneumoniae biofilms. The patchiness of K. pneumoniae biofilms may be due to the fact that this organism is nonmotile. A spatial correlation analysis of the thickness data indicated that thickness measurements were still correlated even when separated by distances that exceeded the mean biofilm thickness. Cell aggregates, some of them hundreds of microns in size, were observed in the effluent of K. pneumoniae and binary population biofilm reactors. Measurements of thickness variability and other observations reported in this article provide a quantitative basis for analysis of microscale structural heterogeneity of biofilms. (c) 1995 John Wiley & Sons, Inc.     

Decrease in tolerance to fenvalerate, in resistantHelicoverpa armigera after pupal diapause

Pyrethroid resistant and susceptible adults ofHelicoverpa armigera (Lepidoptera: Noctuidae) were screened for tolerance to pyrethroids after 6 wk or 12 wk pupal diapuse. Resistant larvae and F₂ larvae from a cross between resistant and susceptible parents (two replicates), were reared under conditions to induce pupal diapause. After eclosion, adults were tested in glass vials coated with the pyrethroid fenvalerate, at a dose (DD) that is known to discriminate between susceptible and heterozygous resistant individuals. In all diapause experiments, the frequency of resistance was lower in the test groups that had experienced diapause compared with the non-diapausing control group. The underlying cause of the decline is not certain but selective mortality of resistant versus susceptible individuals could not account for all the difference in two of the three experiments — tolerance to the pyrethroid, fenvalerate, is most likely to have declined either as a consequence of diapause or from the extended time of development associated with diapause. These results indicate that monitoring programs could underestimate pyrethroid resistance frequencies when usingH. armigera adults emerging from diapause.     

Twins and Q-banded chromosome polymorphisms

Summary Q-banded chromosomal analyses were performed on 24 pairs of twins to determine the stability and heritability of chromosome polymorphisms, and to establish the use of these markers in the determination of twin zygosity. Sixteen twin pairs were determined monozygotic by chromosome polymorphism analysis and confirmed monozygotic by blood group genotyping. No two genetically distinct individuals had the same polymorphic pattern, suggesting the individuality of each morphological karyotype. The frequencies for the various types of chromosome polymorphisms, including stalk length variations, were determined. Analysis of frequency distribution for variant combinations showed random association.     

Structure and Barr body formation of an Xp + chromosome with two inactivation centers.

A patients with seizures, Von Willebrand disease, and symptoms of Turner syndrome was a chromosomal mosaic. In blood culture (1974), 56% of the cells were 45, X 33% 46, XXp+ and 11% 47,XXp + Xp +; in the skin, no cells with 47 chromosomes were found. Presumably the Xp + chromosome arose through a break in the Q-banded dark region next to the centromere on Xp to which an Xq had been attached. The abnormal X was late-labeling and formed a larger than normal Barr body. Of the chromatin-positive fibroblasts, 18.2% showed bipartite Barr bodies, which agrees with the hypothesis that the X inactivation center lies on the proximal part of the Xq. On the basis of the structure and behavior of the bipartite bodies in the present patient, as compared to those formed by other chromosomes with two presumed inactivation centers, we propose that the dark region next to the centromere of Xp remains active in the inactive X. In cells with 45,X and 46,XY, this region has the same relative size, whereas it is significantly shorter in the active X of three females, including the present patient, with one abnormal X. We propose that this region on the active X reveals different states of activity, as reflected in its length, depending on how many other X chromosomes are in the cell.     

A Comparison of Purified Host Specific Toxin from Helminthosporium maydis, Race T, and Its Acetate Derivative on Oxidation by Mitochondria from Susceptible and Resistant Plants

NADH or succinate oxidation and malate oxidation were differentially affected in mitochondria from both susceptible and resistant corn by a purified and chemically characterized preparation of host-specific toxin from Bipolaris (Helminthosporium) maydis, race T. NADH and succinate oxidation by susceptible T corn mitochondria were stimulated 50 to 200% with apparent uncoupling from the cytochrome chain at approximately 10(-9)m toxin (5 to 20 ng/ml). Significant inhibition of malate oxidation was observed at slightly higher toxin concentrations, but oxidation was still coupled to ADP utilization. Inhibition of malate oxidation also was observed in N corn (resistant) and soybean mitochondria at approximately 1,000-fold greater concentrations, but stimulation of NADH and succinate oxidation was not found at any toxin concentration tested.A fully acetylated toxin derivative at approximately 1 microgram per milliliter also caused stimulation of NADH or succinate oxidation in T corn mitochondria, but not those of N corn or soybean mitochondria at 100 micrograms per milliliter. Malate oxidation was inhibited to the same extent by toxin acetate with mitochondria from T corn, N corn, and soybean. The blocking of hydroxyl groups in race T toxin by acetyl functions eliminated selectivity toward malate oxidation only. The data suggest that inhibition of malate oxidation is either a separate or secondary effect of selective action of toxin on T corn mitochondria, perhaps by interference with transport in or out of the matrix. Sensitivity of T, but not N, corn mitochondria to purified toxin decays within minutes after pellets are suspended in aqueous osmotica, with no obvious change in mitochondrial integrity. The action of race T toxin seems to involve a labile process, such as ion gradient(s), or an unstable structural conformation of T corn mitochondria.     

Alkylxanthines: inhibition of adenosine-elicited accumulation of cyclic AMP in brain slices and of brain phosphodiesterase activity.

A series of 1, 3-dialkylxanthines was examined as antagonists of adenosine-induced accumulation of cyclic AMP in guinea pig cerebral cortical slices and as inhibitors of brain phosphodiesterases. The order of potency as adenosine-antagonists was: 8-phenyltheophylline (IC₅₀ 6 μM) > 1, 3-dibutylxanthine (IC₅₀ 30 μM), 1, 3-dipropylxanthine > theophylline (IC₅₀ 60 μM), 3-isobutyl-1-methylxanthine (IBMX), 1, 3, 7-triethylxanthine > 7-benzyl IBMX (IC₅₀ 100 μM), 8-methyl IBMX > 7-benzyl-8-bromo IBMX, 9-methyl IBMX, 8-bromo IBMX, 1-isoamyl-3-isobutylxanthine. The order of potency as inhibitors of brain calcium-dependent phosphodiesterase was: 7-benzyl IBMX (IC₅₀ 1.5 μM), 7-benzyl-8-bromo IBMX > 8-methyl IBMX (IC₅₀ 4.5 μM) > IBMX (IC₅₀ 7.5 μM), 8-bromo IBMX > 9-methyl IBMX (IC₅₀ 40 μM), 1, 3, 7-triethylxanthine > 1, 3-dibutylxanthine (IC₅₀ 100 μM), 1-isoamyl-3-isobutylxanthine > theophylline. 8-Phenyltheophylline and 1, 3-dibutylxanthine represented potent adenosine-antagonists with relatively low activity as phosphodiesterase inhibitors whereas 7-benzyl IBMX and 7-benzyl-8-bromo-IBMX were potent inhibitors of the calcium-dependent phosphodiesterase with relatively low activity as adenosine-antagonists. None of the compounds were potent inhibitors of the brain calcium-independent phosphodiesterase, although 1-isoamyl-3-isobutylxanthine might prove useful as an inhibitor of this enzyme because of its very low activity as an adenosine-antagonist.     

Fatty acid composition of Simonsiella strains

Gas-liquid chromatography of methyl esters of bound fatty acids extracted from the cells of 48 Simonsiella strains showed that these aerobic, gliding, multicellular-filamentous bacteria have fatty acid profiles of the pattern considered typical of Gramnegative eubacteria. All strains contained predominantly tetradecanoic acid (29.5%), 9-hexadecenoic acid (22.2%), an unidentified acid with an equivalent chain length of approximately 20 carbon atoms (15.8%), and dodecanoic acid (11.4%).Discriminant analysis of the mean relative percentages of 12 fatty acids correctly assigned 94% of the strains to groups based on their source of origin (i.e., the oral cavities of sheep, cat, human or dog); the relative amounts of only 3 of the fatty acids (9-octadecenoic acid, hexadecanoic acid, and tetradecanoic acid) provided most of this discrimination.     

Long term effect on mortality of stopping smoking after unstable angina and myocardial infarction.

Subjects who stop smoking cigarettes after myocardial infarction have an improved rate of survival compared with those who continue, but to date it was not known whether the benefit persisted for more than six years. A total of 498 men aged under 60 years who had survived a first episode of unstable angina or myocardial infarction by two years were followed up by life table methods for a further 13 years. Mortality in those who continued to smoke was significantly higher (82.1%) than in those who stopped smoking (36.9%). These differences increased with time. Mortality in those who were non-smokers initially and who continued not to smoke was intermediate (62.1%). The adverse effect of continued smoking was most pronounced in those with unstable angina. Continuing to smoke increased the rate of sudden death to a greater degree in those with less severe initial attacks, while the effect of smoking on fatal reinfarctions was most apparent in those with a more complicated presentation. These findings suggest that stopping cigarette smoking is the most effective single action in the management of patients with coronary heart disease.     

Density-related mortality of the flour beetle,Tribolium confusum duval

Life tables were constructed to assess the relative importance of some factors causing mortality of Tribolium confusum and to gauge their response to increasing population density. Observations focussed on three population densities (100, 400 and 800 individual/8 g medium) from the egg to the adult stage. The medium was not renewed in order to maximize predatory interactions. Generation mortality at densities 100, 400 and 800 was 42%, 50% and 74% respectively, i. e. density-dependent. Mortality in the first 10 days was also density-dependent reaching a maximum of 27% at density 800: predation by small larvae on eggs seemed the principal causative factor. The overall pattern of larval mortality was density-independent. Data on the mortality of pupae and callows were ultimately consistent with an inversely density-dependent pattern. Apparently, only mortality occurring within the first 10 days was capable of population regulation.