Inactivation of Poliovirus Type 1 by the Kelly-Purdy Ultraviolet Seawater Treatment Unit

Three experiments were conducted to determine the effect of ultraviolet (UV) radiation on poliovirus-contaminated seawater. In two of the experiments, the effectiveness of the Kelly-Purdy UV Seawater Treatment Unit to inactivate poliovirus type 1 (T(1)) suspended in continuously flowing seawater was determined. In experiment 1, the observed survival ratio of poliovirus T(1) was 2.3 x 10(-4) (99.98% reduction) in 15.7 sec. No virus was detected (<0.2 plaque-forming unit/ml) in 20.6 seconds. The calculated half-life value was 1.29 sec. In experiment 2, the observed survival ratio of poliovirus T(1) was 5.9 x 10(-4) (99.94% reduction) in 11.7 sec. No virus was detected in 15.7 sec. The calculated half-life value was 1.37 sec. In experiment 3, a laboratory-controlled UV experiment designed to closely simulate the geometry of the continuously flowing seawater system, the observed survival ratios of poliovirus T(1) were 9.7 x 10(-3) (99.03% reduction) and 3.6 x 10(-4) (99.96% reduction) in 15 and 30 sec, respectively; the calculated half-life value was 2.38 sec. A statistically significant difference was found between the inactivation rates of poliovirus T(1) in the two test systems. This rate difference was attributed primarily to UV dosage and stirring effects. The data indicated that UV radiation effectively inactivated poliovirus T(1) in flowing seawater. These results validate the efficacy of the Kelly-Purdy UV Seawater Treatment Unit for use in commercial depuration systems.     

Transduction of Merodiploidy: Induced Duplication of Recipient Genes

Escherichia coli PB160, which carries a tandem duplication with the gene order metB(+)argH(-)su(159) (+)thi(+): metB(+)argH(+)su(159) (-)thi(+), was used to study the mechanism of P1 transduction of genes in the duplicated region. Transduction of the su(159) (+) allele contained within the duplicated segment yields two kinds of su(159) (+) recombinants: 91% are haploid su(159) (+) and 9% are su(159) (+)/su(159) (-) merodiploids. The duplication in these merodiploid transductants includes the metB locus; however, both copies of the metB locus usually are derived from the recipient. Thus, the requirements for transduction of the "condition of merodiploidy" appear to be the cotransduction of the repeat point (the region where the duplication begins to repeat itself) and, of course, the selected marker (in this case su(159) (+)). A mechanism whereby two recipient chromosomes interact with the transduced "repeat point" region to regenerate the tandem duplication is implicated. It appears that a duplication much larger than the quantity of genetic material carried by a P1 phage can be produced in a transductant.     

The chemistry of vitamin B12. The coordination of biologically important molecules

The following equilibrium constants (given as logK in units of m⁻¹) were determined for the substitution of co-ordinated H₂O in aquocobalamin by glycine (bound through N) 5.8, cysteine (bound through S) 6.0 or 8.3, depending on the value chosen for the pK of the thiol group, and phenolate 2.9. The spectrum of the phenolate cobalamin shows an additional intense absorption band at 468nm with a molar extinction coefficient of 1.1×10⁴, which is assigned to a charge transfer from the phenolate to the cobalt ion. Equilibrium constants have also been determined for the equilibria between adenylcobamide cyanide and CN⁻, HO⁻ and H⁺, which show that the adenine is more easily displaced by CN⁻ and HO⁻ than is 5,6-dimethylbenziminazole in vitamin B₁₂, but can be protonated by acid while still remaining co-ordinated to the cobalt. It is shown that in the binding of corrinoids to proteins and polypeptides the formation of hydrogen bonds is far more important than co-ordination by the metal.     

The purine and pyrimidine metabolism of Tetrahymena pyriformis

The metabolism of purines and pyrimidines by the ciliated protozoan Tetrahymena was investigated with the use of enzymatic assays and radioactive tracers. A survey of enzymes involved in purine metabolism revealed that the activities of inosine and guanosine phosphorylase (purine nucleoside: orthophosphate ribosyltransferase, E.C. 2.4.2.1) were high, but adenosine phosphorylase activity could not be demonstrated. The apparent K_m for guanosine in the system catalyzing its phosphorolysis was 4.1 ± 0.6 × 10^?3 M. Pyrophosphorylase activities for IMP and GMP (GMP: pyrophosphate phosphoribosyltransferase, E.C. 2.4.2.8), AMP (AMP: pyrophosphate phosphoribosyltransferase, E.C. 2.4.2.7), and 6-mercaptopurine ribonucleotide were also found in this organism; but a number of purine and pyrimidine analogs did not function as substrates for these enzymes. The metabolism of labeled guanine and hypoxanthine by intact cells was consistent with the presence of the phosphorylases and pyrophosphorylases of purine metabolism found by enzymatic studies. Assays for adenosine kinase (ATP: adenosine 5'-phosphotransferase, E.C. 2.7.1.20) inosine kinase, guanosine kinase, xanthine oxidase (xanthine: O₂ oxidoreductase, E.C. 1.2.3.2), and GMP reductase (reduced-NADP: GMP oxidoreductase [deaminating], E.C. 1.6.6.8) were all negative. In pyrimidine metabolism, cytidine-deoxycytidine deaminase (cytidine aminohydrolase, E.C. 3.5.4.5), thymidine phosphorylase (thymidine: orthophosphate ribosyltransferase, E.C. 2.4.2.4), and uridine-deoxyuridine phosphorylase (uridine: orthophosphate ribosyltransferase, E.C. 2.4.2.3) were active; but cytidine kinase, uridine kinase (ATP: uridine 5'-phosphotransferase, E.C. 2.7.1.48), and CMP pyrophosphorylase could not be demonstrated.     

Genetic Basis of Colicin E Susceptibility in Escherichia coli I. Isolation and Properties of Refractory Mutants and the Preliminary Mapping of Their Mutations

Colicin E-resistant mutants were isolated in Escherichia coli K-12 which, although still apparently possessing the E receptor and adsorbing colicin, were nevertheless insensitive (refractory) to its effect. Eight phenotypic groups were obtained, but some mutants from three of these groups were all shown to map at gal, whereas a second refractory locus, giving resistance to E1 alone, mapped close to thy. It is suggested that the successful fixation of any of the three distinct colicins of group E may involve a dual role for the cell surface "receptor," the first for the binding of the protein and the second for the correct orientation of the bound molecule relative to the cytoplasmic membrane. The majority of the refractory mutants isolated may derive from changes in components concerned with the second of these receptor functions. Two groups of mutants, however, refractory to only E1 or E2, probably reflect changes in the intracellular transmission systems which specifically mediate the effects of these two colicins, the changes not allowing transmission through the cytoplasmic membrane to the respective targets of the colicins. The E1 adsorption site was shown to be distinct from that for E2 and E3, indicating an early separation of the colicin E transmission systems.