High Frequency Transducing Research Articles

Transduction and segregation in Escherichia coli K12

The transduction of the gal + character into gal − mutants of Escherichia coli K12 with high frequency transducing (HFT) lysates of phage λ has been studied. Sensitive recipients infected at low multiplicity give rise to heterogenotes carrying a defective prophage. Simultaneous infection with a non-transducing phage increases the probability of transduction and causes the cell to become lysogenic. Lysogenic recipients upon transduction generally remain lysogenic for the original prophage. Prophage substitution and double lysogenization rarely occur. Loss of the gal + character from the defective lysogenics is generally accompanied by loss of the defective prophage. Loss of the gal + character from the double lysogenics is correlated with changes in prophage content.

Transduction by coliphage λ of the galactose marker

Phages obtained by induction of strain C600 Gal + made lysogenic for λ ++ when infecting strain 112 Gal − sensitive transduce Gal + with low frequency. The strain C600 Gal + is stable; it does not segregate Gal −. The transformed strains are “heterogenotes.” These heterogenotes have the following properties: 1. 1. They are Gal + and lysogenic. 2. 2. They segregate Gal − lysogenic. 3. 3. They do not segregate defective lysogenic or sensitives. 4. 4. They produce primary HFT (high frequency transducing) lysates after induction. These primary HFT lysates have the following properties: 1. 1. The burst size is about 100 phages per bacterium. 2. 2. They produce lytic or lysogenic responses in sensitive cells in the same proportion as normal lysates. 3. 3. Among the lysogenized cells there are a large number which have been transformed to Gal +. 4. 4. All the Gal + are lysogenic. 5. 5. The “Gal + titer” of the lysate is much higher than the titer of the induced bacteria which produced the lysate. 6. 6. When the primary HFT lysate is passed through one cycle of growth on C600 Gal + sensitive, on 112 Gal + sensitive, or on Gal − sensitives, the phage titer and the Gal + titer go up nearly in parallel; the efficiency of multiplication of HFT in the Gal − cells seems smaller than in the Gal + cells. 7. 7. The HFT lysate transduces Gal + into 112 Gal − lẏsogenic cells with a much lower efficiency than they transduce it into sensitive cells. 8. 8. All these transformed lysogenic cells are heterogenotes and the vast majority of them, upon induction, liberate HFT lysates whose phages do not have the genetic markers of the phages used to transform them, but have the genetic markers of the prophage that was carried by these cells.