Conclusions
In conclusion, we have developed a new counter-selection system based on
lysis gene E . In view of the generic lethality to Gram-negative
bacteria, it is very promising to be a universal alternative for genomic
seamless modification. Counter-selection cassette based on lysis geneE under two sets of
expression regulation system, cI/pL and Arac/PBAD, were
developed to adapt to different hosts. Seamless modification was
conducted successfully and the highest selection stringency so far was
obtained both in E. coli and in S. marcescens .