The tetracycline resistance plasmid pCF10 (58 kilobases [kb]) of Streptococcusfaecalis possesses two separate conjugation systems. A 25-kb region of the plasmid (designated TRA) was shown previously to determine pheromone response and conjugation functions required for transfer of pCF10 between S. faecalis cells (P. J.Christie and G. M. Dunny, Plasmid 15:230-241, 1986 from the chromosome to various sites on the streptococcal plasmid pAD1 (5,14).Recent work in one of our laboratories resulted in the generation of a physical and genetic map of the pheromoneinducible conjugative S. faecalis tetracycline resistance plasmid pCF10 (4). The major features of this plasmid include a 25-kb region (designated TRA) that determines plasmid transfer and pheromone response functions. A distinct 16-kb region containing the tetracycline resistance determinant (Tet9) showed a high degree of sequence-homology with the conjugative transposon Tn916 (14, 15). However, we were unable to ascribe any of the genetic functions that would be predicted for a conjugative transposon to this region of pCF10. Of particular significance is the stability of the Tetr determinant and its continued association with pCF10 through multiple rounds of conjugative transfer. In contrast, when Tn916 and related elements are inserted into conjugative plasmids, they commonly excise and segregate from these plasmids at high frequency (by a proposed zygotic induction mechanism) (16)

The effects of tetracycline on transfer of the conjugative, tetracycline-resistance transposon. Tn925, as well as the ability of the transposon to promote the transfer of chromosomal genes was examined in Enterococcus faecalis and Bacillus subtilis. To test for chromosomal transfer, multiply-marked strains of each organism, each carrying a single chromosomal copy of Tn925, were mated on filters with suitable recipient strains, under conditions where transformation and transduction were precluded. In both cases, transfer of a variety of chromosomal genes, at frequencies comparable to the frequency of Tn925 transfer, was detected readily. The presence of Tn925 in one of the members of the mating pair was absolutely required for chromosomal transfer, but transfer of Tn925 did not accompany every chromosomal transfer event. The results were consistent with a mating event resembling a type of cell fusion, allowing for extensive recombination between the genomes of the mating partners. Growth of Tn925-containing donor cells in the presence of tetracycline increased the transfer frequency of Tn925 by about tenfold in E. faecalis, but not in B. subtilis.

The attachment site for the prophage of SP,8 lies between ilvA and kauA on the chromosome of Bacillus subtilis strain 168. Specialized transduction of citK and kauA can be carried out by certain lysates of SPJ3. It has recently been found (F.

Cultures of Bacillus subtilis lysogenic for the temperature bacteriophage SP beta release "betacin", a bacteriocinlike substance that inhibits B. subtilis strains which do not carry this phage. Production of betacin is blocked by mutations in the bet gene on the prophage and a second phage gene, tol, is apparently involved in making the lysogen itself tolerant to betacin. Mutations in a bacterial gene betR, located on the B. subtilis chromosome between metC and pyrD, render nonlysogens tolerant to betacin.

KORMAN, RUTH Z. (Cornell University, Ithaca, N.Y.). Coagulase-negative mutants of Staphylococcus aureus: genetic studies. J. Bacteriol. 86:363-369. 1963.-The behavior in mutation and transduction of pleiotropic coagulase-negative mutants of Staphylococcus aureus PS 53 (NCTC 8511) was analyzed. Coagulase-positive colonies were recovered, as well as a novel phenotype resistant to some cell-wall inhibitors and differing in sugar fermentation pattern. The hypothesis that the coagulase-negative strains differ from the original propagating strain in the structure or organization of the cell wall is discussed.