Concurrent changes in transducing efficiency and content of transforming deoxyribonucleic acid in Bacillus subtilis bacteriophage SP-10.

Taylor, Martha J. (Fort Detrick, Frederick, Md.), and Curtis B. Thorne. Concurrent changes in transducing efficiency and content of transforming deoxyribonucleic acid in Bacillus subtilis bacteriophage SP-10. J. Bacteriol. 91:81-88. 1966.-Spores of Bacillus subtilis W-23-S(r) infected with transducing phage SP-10 served as convenient inocula for broth cultures from which transducing phage was harvested. Methods are described for producing highly infected spores. The inoculum level of infected spores in nutrient broth-yeast extract-glucose medium affected the transducing efficiency of SP-10 in lysates of these cultures. Phage in lysates of cultures inoculated with about 10(5) or fewer spores per milliliter transduced 20- to 350-fold more efficiently than did phage in lysates from cultures inoculated with 10(6) to 10(7) spores per milliliter. Transduction frequencies in the order of 10(-5) per plaque-forming unit were obtained routinely, and some infected-spore preparations yielded phage that gave frequencies as high as 10(-4). The combination of inoculum level and incubation time required to produce the best transducing phage had to be determined empirically for each batch of infected spores. Several possible explanations for the difference between lysates having high (HTE) and those having low (LTE) transducing efficiency were ruled out by special experiments. The hypothesis is presented that some cultural condition resulting from a relatively low inoculum of phage-infected spores favors the incorporation by phage particles of bacterial deoxyribonucleic acid (DNA) in the manner required for the production of transducing phage. Support for this hypothesis is a demonstration, through transformation experiments with DNA extracted from HTE and LTE phage particles, that populations of HTE phage particles yielded significantly more (7 to 27 times) transforming activity per microgram of DNA than did populations of LTE phage.