Behavior of three colicine factors and an R (drug-resistance) factor in Hfr crosses inSalmonella typhimurium

Abstract

An LT2 Hfr strain,his metC gal, was crossed to a multiply marked LT2 F⁻line. Analysis of recombinant yields, segregation of unselected markers and interrupted matings indicated injection of the Hfr chromosome in the sequence The introduction into the Hfr of the colicine factorscolI, colE1andcolE2and the R factorR2had little or no effect on its fertility. All four factors were transmitted at low frequency to the F⁻population, and to recombinants at higher frequencies (colI5–30%,colE130–80%,colE25–30%,R20–9%). Transfer ofcolE1occurred before 20 min., that ofcolE2andcolIlater than 100 min. Segregation data did not reveal close linkage of any factor to any chromosomal locus, but recombinants with a long stretch of donor chromosome were more likely than others to have acquiredcolE2andcolI. Nearly all recombinants andF⁻cells which acquiredcolIorcolE2acquired both, andcolE1also. Most cells which acquiredR2acquired one or more colicine factors. These plasmid associations can be formally represented by transfer of plasmids, independently of the chromosome, in the sequencecolE1—(colI, colE2)—R2. Phage P22 grown on the Hfr carrying the four plasmids transduced thetet-rtrait ofR2at very low frequency, and thesul-r str-rcharacters, together, at low frequency. Some of each sort of drug-resistance transductant, but no transductants in respect of chromosomal characters, acquiredcolEl or colE2by co-transduction.