Lysogenic strains of Bacillus subtilis 168 were reduced in their level of transformation as compared to non-lysogenic strains. The level of transformation decreased even further if the competent lysogenic cells were allowed to incubate in growth media prior to selection on minimal agar. This reduction in the frequency of transformation was attributable to the selective elimination of transformed lysogenic cells from the competent population. Concurrent with the decrease in the number of transformants from a lysogenic competent population was the release of bacteriophage by these cells. The lysogenic bacteria demonstrated this dramatic release of bacteriophage only if the cells were grown to competence. Both the selective elimination of transformed lysogens and the induction of prophage was prevented by the inhibition of protein synthesis. Additionally, competent lysogenic cells released significantly higher amounts of exogenous donor transforming deoxyribonucleic acid than did competent nonlysogenic cells or competent lysogenic cells incubated with erythromycin. These data establish that the induction of the prophage from the competent lysogenic cells was responsible for the selective elimination of the lysogenic transformants. A model is presented that accounts for the induction of the prophage from competent lysogenic bacteria via the induction of a repair system. It is postulated that a repair system is induced or derepressed by the accumulation of gaps in the chromosomes of competent bacteria. This hypothetical enzyme(s) is ultimately responsible for the induction of the prophage and the selective elimination of transformants. Lysogenic conversion can markedly influence the capacity of a wide range of bacterial species to undergo deoxyribonucleic acid (DNA) mediated transformation and transfection. For instance, Staphylococcus aureus can be made competent only in the presence of temperate bacteriophage 441 (29, 34). Similarly, Bacillus stearothermophilus requires the temperate bacteriophage TP-12 for the development of competence (N. E. Welker and M. E. Eager, Abstr. Annu. Meet. Amer. Soc. Microbiol. 1972, V98, p. 201). Apparently this virus enables the cell to produce the competence factor(s) required for the binding of DNA to the cytoplasmic membrane (38). On the other hand, in Bacillus subtilis (27, 44, 45, 47) and streptococci (25), lysogeny inhibits DNA-mediated transformation. Although transformation is reduced in competent lysogenic cultures of B. subtilis,

Cultures of Bacillus subtilis developed competence for the uptake of deoxyribonucleic acid in a chemically defined medium with a predictable, reproducible pattern. The gross effects of individual amino acids were determined. Seven amino acids, most of which are reported to be major components of the cell wall, were shown to impair the development of maximal levels of competence. When the synthetic growth medium was supplemented with a mixture of the nine amino acids which we found to stimulate the development of competence, the level of transfection was increased to 10 to 15% of the population. The actual level of competence in these populations was assayed by transformation of unlinked bacterial markers and by two different transfection assays. The results indicate that calculations from cotransfer of unlinked markers overestimates the degree of competence in highly competent populations of B. subtilis, whereas the number of plaques obtained in transfection is an underestimate of the actual level of competence. The results are interpreted to indicate that neither method of analysis gives a true estimate of the competent population, but that more than 80% of the cells may be competent.

Strains of Bacillus subtilis lysogenic for either temperate bacteriophage X105 or SP02 were reduced to less than 1.0% of the level of transformation of the nonlysogenic strains. Strains lysogenic for both 4105 and SP02 are virtually nontransformable, indicating that the effect of lysogeny is additive. Lysogenic cultures transfected at essentially wild-type levels with deoxyribonucleic acid (DNA) isolated from bacteriophages 029 and SPOl. The residual transforma

Preoperative CT and MR angiography of the renal arteries in renal donors demonstrate substantial agreement. Interobserver disagreement in the interpretation of CT and MR angiograms is related to 1-2-mm-diameter vessels.

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