Vol. 127, No. 2 Printed in U.S.A.
JouRNAL oF BACThROLOGY, Aug. 1976, p. 829-831 Copyright © 1976 American Society for Microbiology
Low-Frequency, PBS1-Mediated Plasmid Transduction in Bacillus pumilus MICHAEL G. BRAMUCCI AND PAUL S. LOVETT* Department of Biological Sciences, University ofMaryland Baltimore County, Catonsville, Maryland 21228
Received for publication 10 March 1976
Three bacteriophages were tested for ability to transduce the plasmid pPL10 between W mutant derivatives of Bacillus pumilus NRS 576. Phage PBP1- and PMB1-generated plasmid transductants occurred at about 10% the frequency of transductants for a chromosome marker. Phage PBS1-generated plasmid transductants occurred at less than 0.1% the frequency oftransductants for a chromosome marker. Possible reasons for the extremely reduced capacity of PBS1 to generate plasmid transductants are discussed. Bacteriophage PBS1 was originally isolated as a transducing virus for strains of Bacillus subtilis (14). PBS1 also infects related Bacillus species, including strains of B. licheniformis and nearly one-third of the B. pumilus strains examined (7). The usefulness of PBS1 as a generalized transducing phage results, in part, from the fact that virus particles can accommodate a deoxyribonucleic acid (DNA) molecule (-1.8 x 1O8 daltons) equivalent to nearly 10% of the estimated molecular weight of the B. subtilis chromosome (2, 4, 5, 15). In the absence of a conjugation system in Bacillus, PBS1 has been essential for establishing linkage between genes located relatively far apart on the host chromosome (17). Indeed, the recent demonstration of a circular genetic map for B. subtilis is based on PBS1 transduction (6). Although the characteristics of PBS1 transduction of chromosomal genes have been studied in B. subtilis and B. pumilus (13), PBS1mediated transduction of: plasmids had not been previously examined. This -results from the fact that plasmids known to be harbored by PBS1-sensitive strains ofB. subtilis or B. pumilus either determine a host characteristic that does not permit positive selection of plasmidcontaining transductants (e.g., the reduced capacity for sporulation, reference 8) or the plasmids govern no known host function (10, 11). We recently described the properties of a small plasmid, approximately 4.4 x 106 daltons, that determines the production of, and immunity to, a killing activity in a PBS1-insensitive strain of B. pumilus (12). Transfer of this plasmid, pPL10, to a PBS1-sensitive strain of B. pumilus was accomplished by transduction with phage PBP1 (12). In the present study we compared the ability of three transducing
phages to transfer plasmid pPL10 in a strain of B. pumilus. The results indicate that two of the phages, PBP1 and PMB1, generated plasmid transductants at about one-tenth the frequency of transductants for an individual chromosomal marker. With the PBS1 transduction system, however,.transductants for the plasmid marker occurred at
JouRNAL oF BACThROLOGY, Aug. 1976, p. 829-831 Copyright © 1976 American Society for Microbiology
Low-Frequency, PBS1-Mediated Plasmid Transduction in Bacillus pumilus MICHAEL G. BRAMUCCI AND PAUL S. LOVETT* Department of Biological Sciences, University ofMaryland Baltimore County, Catonsville, Maryland 21228
Received for publication 10 March 1976
Three bacteriophages were tested for ability to transduce the plasmid pPL10 between W mutant derivatives of Bacillus pumilus NRS 576. Phage PBP1- and PMB1-generated plasmid transductants occurred at about 10% the frequency of transductants for a chromosome marker. Phage PBS1-generated plasmid transductants occurred at less than 0.1% the frequency oftransductants for a chromosome marker. Possible reasons for the extremely reduced capacity of PBS1 to generate plasmid transductants are discussed. Bacteriophage PBS1 was originally isolated as a transducing virus for strains of Bacillus subtilis (14). PBS1 also infects related Bacillus species, including strains of B. licheniformis and nearly one-third of the B. pumilus strains examined (7). The usefulness of PBS1 as a generalized transducing phage results, in part, from the fact that virus particles can accommodate a deoxyribonucleic acid (DNA) molecule (-1.8 x 1O8 daltons) equivalent to nearly 10% of the estimated molecular weight of the B. subtilis chromosome (2, 4, 5, 15). In the absence of a conjugation system in Bacillus, PBS1 has been essential for establishing linkage between genes located relatively far apart on the host chromosome (17). Indeed, the recent demonstration of a circular genetic map for B. subtilis is based on PBS1 transduction (6). Although the characteristics of PBS1 transduction of chromosomal genes have been studied in B. subtilis and B. pumilus (13), PBS1mediated transduction of: plasmids had not been previously examined. This -results from the fact that plasmids known to be harbored by PBS1-sensitive strains ofB. subtilis or B. pumilus either determine a host characteristic that does not permit positive selection of plasmidcontaining transductants (e.g., the reduced capacity for sporulation, reference 8) or the plasmids govern no known host function (10, 11). We recently described the properties of a small plasmid, approximately 4.4 x 106 daltons, that determines the production of, and immunity to, a killing activity in a PBS1-insensitive strain of B. pumilus (12). Transfer of this plasmid, pPL10, to a PBS1-sensitive strain of B. pumilus was accomplished by transduction with phage PBP1 (12). In the present study we compared the ability of three transducing
phages to transfer plasmid pPL10 in a strain of B. pumilus. The results indicate that two of the phages, PBP1 and PMB1, generated plasmid transductants at about one-tenth the frequency of transductants for an individual chromosomal marker. With the PBS1 transduction system, however,.transductants for the plasmid marker occurred at
