Construction of a DNA probe to detect isoquinoline-degrading bacteria

To facilitate the cloning of DNA encoding isoquinoline degradation an assay was developed that allowed the rapid visual scoring of the isoquinoline degradation phenotype of single colonies. Transposon mutagenesis of one of the isolates. Comamonas acidovorans IQ3, was performed using Tn5, and nine Isq-mutants deficient in the ability to utilise isoquinoline as the sole nitrogen source were isolated. These mutants were also incapable of utilising the first metabolite of the isoquinoline degradation pathway, 1-hydroxyisoquinoline, as the sole carbon source. For each Isq-mutant, the EcoRI fragment containing the Tn5 insertion was cloned into pBR322. Restriction and Southern analyses of the cloned DNA revealed that of the nine Isq-mutants, six contained Tn5 insertions in a common 8.9-kb EcoRI fragment derived from the wild type, C. acidovorans IQ3. The cloned DNA thought to be involved in the degradation of isoquinoline proved to be specific when used as a probe in colony hybridization to some bacteria possessing the ability to degrade isoquinoline.     

Effect of inhibitors on flammability range of flames produced from LPG/air mixtures

Burning velocities of Liquefied Petroleum Gas/air flames of different fuel/air compositions have been measured by the flat-flame method originally developed by Egerton and Powling, and the effects of inhibitors such as chlorinated hydrocarbons (chloroform, methylene dichloride, carbon tetrachloride) on the burning velocities have been investigated. The flammability limits at different fuel/air compositions have also been measured. The difference between upper and lower limits of flammability was narrowed by the addition of inhibitors in the order carbon tetrachloride chloroform methylene dichloride, i.e. the inhibiting effect increased with increase in the number of chlorine atoms. The relative effectiveness of different inhibitors has been expressed as an inhibition efficiency, and it has been found that an interesting correlation exists between the inhibition efficiency (also the narrowing of limits, and the maximum burning velocity) and the number of (dissociable) chlorine atoms present in the molecule of inhibiting compound. Other factors were the degree of dissociation of the inhibiting molecule in the flame, and the concentration of the inhibitor in the fuel/air mixture; the effect of small concentrations was that of specific chemical inhibition whereas at higher concentrations dilution effects were dominant. At the upper limit the flame has maximum tendency to flash back in an ordinary burner and the combustion wave may develop into a detonation wave inducing an explosion hazard. Hence upper explosion limit may be considered an index of explosion risk. The inhibitors lower this largely by reducing the concentration of free radicals in the flame boundary, increasing the difficulty of ignition, and thus increasing safety. A large difference has been found between the experimental and calculated value of the upper limit for the pure gas, probably owing to the chemical effects of ethylene via production of acetaldehyde which catalyses the combustion.