I used to grow a microRNA vector in E. coli and the protocol suggested sanger sequencing of the insert region after bacterial transformation as about 20% of vectors contain errors. I can confirm that happened to me as well. I would imagine this would be relevant for you as well as a mutation in its sequence could affect your antibody (missense/non-synonymous mutations/in-dels).

In general they are quite stable because the vast majority of the plasmid copies do not mutate . Although eventually any plasmid could change, at a low frequency. Did you find any problem? Which is exactly the reason for your question? If you have aby doubt, sequencing can tell you the truth about your plasmid.

First of all, thank you both for your reactions. I did not run into any problems with my experiments, but I was just having random thoughts (and please correct me if I am wrong). In vivo, you get the highest diversity from antibodies due to mutations, I thought that in panning, if you let the cells grow on long enough, you can get a similar effect (that is if you are lucky with the place of the mutations) in gaining more diversity and maybe more lucky hits for your targets.

Some host cells are more stable than others, but Gertrudis is correct in advising that you confirm the sequence after transfection and selection of single clones. Typically from the confirmed transfection, we would grow up batches and freeze down, then use a batch for a limited time. if you wanted to be very careful, it would be easy to confirm the sequence from each new batch that you use.

Diversity introduction in antibodies is not linked to the low mutation rate during DNA replication. It is a highly regulated process taking place at some stages of lymphocyte development and targeting specific variable region gene sequences (thats why it is called somatic HYPERmutation). I dont think this process can be reproduced during normal plasmid replication in bacteria.The attempts to do so in some way have involved mutation-prone strains with a higher mutation rate or amplification steps between selection rounds using error-prone polymerase. In mammalian display (based on mammalian cells displaying antibodies rather than phages), I think there are examples where host cells have been engineered to express enzymes involved in somatic hypermutation, trying to resemble the natural process.

As Gertrudis stated, you shouldn't rely on the mutations introduced by E. Coli to introduce diversity into your antibody, our immune system also uses splicing to further enhance diversity which bacteria cannot do. Depending on your application, introducing diversity may not be a good idea i.e. when trying to synthesize a monoclonal antibody.