DNA binding and entry during transfection in Streptococcus pneumoniae

Conditions to enhance transfection in Streptococcus pneumoniae

Enhancement of transfection in the wild-type strain of Streptococcus pneumoniae, which contains normal levels of nucleases, can be achieved by a careful control of the components of the medium. Protection of the donor DNA against the degradation by the nucleases present at the surface of the cell during the adsorption to the physiologically competent bacteria is a necessary condition to obtain an enhanced transfection. Using [3H]thymidine-labeled Dp-4 DNA we have found that maximal levels of DNA uptake and a remarkable stimulation in genetic transfection were obtained in the presence of calcium ions. Concentrations of magnesium ions higher than 2 mM stimulated the extracellular degradation of the donor DNA and inhibited transfection.

Isolation and characterization of a new bacteriophage, Cp-1, infecting Streptococcus pneumoniae

Several pneumococcal phages showing a morphology completely different from those of all other previously found pneumococcal bacteriophages have been isolated. Bacteriophage Cp-1, one of the phages isolated, showed an irregular hexagonal structure and a short tail of 20 nm. The virion density was 1.46 g/cm3. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the presence of nine polypeptides. The polypeptide showing a molecular weight of 39,000 accounted for more than the 90% of the total protein. The nucleic acid of Cp-1 was linear, double-stranded DNA with a mean length of 6.3 microns and a guanine-plus-cytosine content of 41%; its buoyant density was 1.699 and 1.422 g/cm3 in CsCl and CS2SO4, respectively. Its sedimentation coefficient (S20,w) was 19S. Cp-1 DNA showed a remarkable resistance to a large number of restriction endonucleases. A total of 12 fragments, ranging in molecular weight from 1.3 X 10(6) to 0.09 X 10(6), were produced by AluI, two fragments (molecular weight, 5.5 X 10(6) and 0.9 X 10(6)) were generated by HindIII, and two fragments (molecular weight, 6.0 X 10(6) and 5.7 X 10(6)) were produced by HaeIII. The easy visualization of th plaques produced by Cp-1, the small size of Cp-1 DNA (12 X 10(6) daltons), and other biological and physiochemical properties make this phage potentially useful for genetic studies.