Integration of foreign genetic material provokes local mutagenesis in the recipient genome

Exchange of genetic material is a key factor of evolution in bacteria, though the mechanisms of integration of horizontally acquired genes into the regulatory networks of the new host remain practically uninvestigated. The present study is devoted to analyzing this adaptation and, in particular, involvement of the bacterial transcription machinery in this process. Therefore, two foreign genes in the genome of Escherichia coli K12 MG1655 were substituted with their copies taken from the genomes of presumed donor bacterium, and long-term growth of mutant and control cultures was initiated. Following 2000 (for gene sfmA) and 4000 (for gene ydhZ) generations, the modified and native genomic regions were amplified and used for population sequencing. Spontaneous mutations were analyzed, and it was found that substitutions of G/C- to A/T-pairs occurred more frequently in the modified regions as compared to non-modified, whereas A/T $\to$ G/C substitutions were rarer. This implies that the host genome responds to integration of foreign genetic material with an adaptive reaction aimed to enrich the modified region with A/T-pairs. In the course of long-term evolution, it may result either in “silencing” of an adverse gene with the involvement of H-NS — a specific suppressor of foreign genes, or in the creation of a suitable promoter within a promoter island for adequate expression of useful gene.