Correlation between the occurrence of competence in the transformation of group H Streptococci and the presence of the competence factor and the in vitro DNA-inactivating factor

Genetic transformation in Streptococcus sanguis. Competence factor and competence factor inactivator

Genetic transformation in Streptococcus sanguis is a complex, multi-step process, involving several factors. The competence factor (CF), occurring in the culture filtrates of some strains, is essential in streptococcal transformation, but other factors are also involved. The presence of serum during growth is not obligatory for the preparation of active culture filtrate, but serum increases the amount and duration of CF activity of some strains. The stability of the CF activity differs distinctly in filtrates prepared from various strains. This observation can be explained by the presence of a previously undescribed factor--names the competence factor inactivator (CFI)--which inactivates the CF in culture filtrates during the transforming experiment as well as during storage. The CFI is thermolabile and is estimated from the filtrates by heating (65 degrees C for 15 min). The properties of the CFI suggest that it may be a protein with enzymatic activity. The CFs from the strains Challis and 13b resist heating to 100 degrees C for 2 h, and are stable for at least 72 h if the CFI is absent or has been inactivated by heating. The CF activity in the filtrates is inactivated by pronase and chymotrypsin, suggesting that the CF may be of a polypeptide nature.

Purification and properties of deoxyribonucleic acid binding factor isolated from the surface of Streptococcus sanguis cells

Deoxyribonucleic acid (DNA) binding factor (BF) was found in surface fluids from competent and noncompetent cells of Streptococcus sanguis strains Challis, Wicky, and Blackburn. Fluids from noncompetent cells exhibited about 10% BF activity compared with extracts from competent cells. BF from competent Wicky cells was purified to homogeneity by electrophoresis and immunodiffusion. Purified BF preparations exhibited slight endonucleolytic activity, directed mainly against single-stranded DNA. Nucleolytic and DNA binding activities present in purified BF could be separated by polyacrylamide gel electrophoresis. Purified BF was sensitive to proteolytic enzymes and to phospholipase D, and its activity was stimulated in the presence of low Triton X-100 concentrations. The protein component of BF is a single, monomeric polypeptide with a molecular weight of 56,000 and an isoelectric point of pH 5.8. Binding of purified BF to DNA was a very rapid process at the optimum temperature, pH, and ionic strength and led to the formation of fast-sedimenting complexes. Purified BF was tested for several properties. It exhibited higher affinity to single- than to double-stranded DNA. It bound poorly to glucosylated phage T4 and single-stranded, synthetic polydeoxyribonucleotides and did not bind to RNA. It protected single-stranded DNA against nuclease S(1) action but did not protect native DNA against deoxyribonuclease I action. No evidence was found for unwinding activity, using double-stranded DNA as a substrate.

Effect of pH on competence development and deoxyribonucleic acid uptake in Streptococcus sanguis (Wicky)

Streptococcus sanguis (Wicky) cells, strain WE4, developed little or no competence and failed to autolyze in permissive conditions when treated with competence factor (CF) below PH 7.0. This lack of activity was directly correlated with the inability of the cells to bind or take up CF at pH values of 5.5, 6.0, and 6.5. On the other hand, competent cells bound deoxyribonucleic acid molecules maximally below pH 7.0 and transformed maximally at pH 6.5. Deoxyribonucleic acid was optimally bound to cells in a deoxyribonuclease-resistant form at pH values between 7.0 and 8.5. Concomitant with this binding, undefined acid-soluble DNA fragments appeared in the culture menstrua. CF binding and uptake by cells was not only influenced by low pH but also by low temperature. At 0 C, WE4 cells bound only 4% of the input CF and took up less than 1% into a trypsin-insensitive state compared to cells treated at 37 C. Cells treated with CF at 0 C did not autolyze when transferred to permissive conditions. The results presented in this report extend earlier findings that showed that competence development and autolysis are related to the uptake of CF.

Nuclease content of group H Streptococcus strain Challis cell surface extracts inactivating transforming deoxyribonucleic acid

Besides the competence factor (cpf), the activity of nuclease present in cell surface extracts (iF) is most likely necessary for the occurrence of competence in transformation of Challis strain and other group H streptococci. Very small amounts of iF activity were available. For this reason there were no data on nucleases occurring in iF preparations. In our previous studies, three deoxyribonucleases (endonucleases) were isolated and partly purified from stationary Challis strain cells. In the present work, due to the application of stationary-phase cell endonucleases, gel electrophoresis, and the immunological method, we found that two of these nucleases occur in Challis strain iF preparations. These two nucleases are present in larger amounts at the cell surface only in cells originating from the early-logarithmic-phase culture. Only in this phase does competence occur in the Challis strain. Antibodies against the three endonucleases of the Challis strain do not block the occurrence of competence. We suggest that an increase in the permeability of the cell membrane for intracellular nucleases independent of cpf activity is a stage in the maturation of competence.

Identification of a deoxyribonuclease implicated in genetic transformation of Diplococcus pneumoniae

A mutation of Diplococcus pneumoniae, end-1, reduces the major deoxyribonuclease activity of the cell, an endonuclease, to 10% of its normal value without impairing transformation. Further mutations, called noz, abolish the residual endonuclease activity and block transformation. The residual endonuclease is similar to the wild-type enzyme in size, charge, divalent cation dependence, inhibition by ribonucleic acid, and formation of oligonucleotide products. However, the mutant endonuclease is more temperature sensitive, which suggests that the end-1 mutation occurred in a structural gene for the enzyme. Genetic analysis showed that the noz mutations occur at the same genetic locus. A number of new end mutants were analyzed. Those that retained more than 1.4% of the normal endonuclease activity were essentially normal in transformation; those with less than 1% were defective. The transformation-defective end mutants appear to be blocked in the entry of deoxyribonucleic acid (DNA) since they carry out the prior step of binding DNA to the outside of the cell. The major endonuclease of the cell may act as a DNA translocase by attacking and degrading one strand of DNA, thereby facilitating entry of the complementary strand into the cell.

Temporary, reversible binding of the competence factor to cellular receptors of Pneumococcus during induction of competence

The binding of the competence factor to cellular receptors of physiologically non-competent cells of Pneumococcus was followed as a function of time. A transformation medium without bovine serum albumin was used to study the binding of the competence factor. Control cells without the added factor remained completely non-competent under these conditions. The maximal binding of the factor to the cellular receptors took place already after 3 min of contact of the cells with the factor at 37 degrees C. After 10 min, when the maximum induction of competence occurs in the system used, the competence factor is fully released from the receptors to the medium. It follows that within the period between the 3rd and 10th min, when the cells are being modified for the irreversible binding of DNA, the presence of the competence factor on the cells is no longer necessary.

Early events in development of streptococcal competence

Appropriately timed use of trypsin, which inactivates competence factor (CF), and chloramphenicol made feasible a separation and characterization of early events in the development of competence in group H streptococci. Step 1 is production of CF, which is inseparable in time from the concomitant release of free CF into the medium. The producing cells, which are noncompetent at the time, also accumulate cell-bound CF (CB-CF) from the onset of CF synthesis. In step 2, the released CF is adsorbed or taken up in a trypsin-insensitive state by the producing cells and is not destroyed as previously suggested. This occurs rapidly in a transformation-supporting (complete) medium. The rapid decline in free CF is concomitant with the rise in CB-CF, and a maximal increase in the latter does not occur in cultures exposed to trypsin, which inactivates any trypsin-accessible CF. The rapid increase in CB-CF (above trypsin-treated levels) leads to step 3, the induction of competence. All of these steps probably require protein synthesis, because each is inhibited by chloramphenicol. The data also indicate that only free CF that is subsequently adsorbed, and which thus leads to maximal levels of trypsin-insensitive CB-CF, is the effective inducer of competence in either CF-producing (Challis) or CF-nonproducing (Wicky) cultures. The processes induced by the newly bound CF are not fully understood, but certain new properties, previously described by others as indicating competence, were measured during the several steps of competence development. Cell aggregation at pH 2 appears to be related to CB-CF and can be shown before this bound CF has induced competence. The ability of cultures to autolyze maximally can be diminished by trypsin treatment of precompetent cells without affecting subsequent competence development as measured by transformation.

Transformation in group H streptococci: blackburn strain transformable mutants

Transformable mutants of the nontransformable Blackburn strain group H streptococci have been isolated. In contrast with the wild strain, the cell surface extracts of these mutants contain the factor inactivating deoxyribonucleic acid in vitro.