plasmid transduction

This morning, I read some referrences about plasmid transduction. Plasmid transduction is using phages extracted from hosts harboring a plasmid transducts a receptor strain and screen the transductants expressing the plasmid marker. This means that the plasmid has recombined to the phage when the phage enter into the host, and that plasmid can be carried into cells on the phage vector.

It might not be surprising from the perspective of bacteriophage infection. But the addition of plasmid can change the infection behavior of phage infection and different plasmids have different abilities of plasmid transduction while the recombination frequency in the host cell keep the same. Whats more, recA is not required for plasmid transduction behavior. All these phenomenon strongly suggest that plasmid in itself affect the infection process.

For natural transformation, phages may know more than us. Maybe phage just makes full use of this mechanism to circumvent the two membrane barrier. Although phages adopt various strategies to pass through the barriers, in the final stage they will have to let their DNA/RNA to cope with the plight. Some lucky phage DNA can be sent to periplasm and face only the inner membrane while some other phage DNA has to face the first membrane as soon as they were released from the phage capsule. Nevertheless, phage DNA (I thinkt there should be no difference between plasmid DNA) must have learned the capability of passing through membranes and capsules and proteins encoded by genes on phage genome just aid DNA entering and enhance the chance of entering and surviving in the host.

Recently, someone argued that RNA virus might be the ancestor of all organism in the earth. Considering that RNA virus is not stable and can be easily degraded, I support the idea that DNA virus should be the ancestor, locating at the root of the evolution tree. It is possible that DNA gradually evolved to DNA virus.