Abstract
It is usually thought that bacteriophage T7 is female specific, while phage T3 can propagate on male and female Escherichia coli. We found that the growth patterns of phages T7M and T3 do not match the above characteristics, instead showing strain dependent male exclusion. Furthermore, a T3/7 hybrid phage exhibits a broader host range relative to that of T3, T7, as well as T7M, and is able to overcome the male exclusion. The T7M sequence closely resembles that of T3. T3/7 is essentially T3 based, but a DNA fragment containing part of the tail fiber gene 17 is replaced by the T7 sequence. T3 displays inferior adsorption to strains tested herein compared to T7. The T3 and T7 recombinant phage carries altered tail fibers and acquires better adsorption efficiency than T3. How phages T3 and T7 recombine was previously unclear. This study is the first to show that recombination can occur accurately within only 8 base-pair homology, where four-way junction structures are identified. Genomic recombination models based on endonuclease I cleavages at equivalent and nonequivalent sites followed by strand annealing are proposed. Retention of pseudo-palindromes can increase recombination frequency for reviving under stress.
Highlights
Bacteriophages of the T7 group consist of a large number of related phages that grow on Escherichia coli and other bacterial genera
We show that the propagation of a T7 Meselson (T7M) phage varies on different host strains of E. coli, not conforming to the features of T7
The sizes of plaques of T3 and T7M are similar for the phage growing on BL21 and DH5a (,0.4 cm), but the size (,0.2 cm) of T3/7 on DH5a is only half of that on BL21
Summary
Bacteriophages of the T7 group consist of a large number of related phages that grow on Escherichia coli and other bacterial genera. The complete nucleotide sequences of gene 1.2 of the T7M and T3/7 phages are identical to that of the T3. The amino acid sequences of the N-terminal domain (residues 1–149) that interacts with the tail-tube have high homology between T3 and T7, only residues 48 and 118 are different, both incur an Ala to Thr substitution from T3 to T7.
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