Studying the effects of natural transformation on the adaptation of B. subtilis through experimental evolution

Natural transformation has evolved in some species of bacteria as means to introduce foreign-DNA into the self-DNA via homologous recombination. The Lateral transfer of DNA and its effect on bacterial evolution have been extensively studied in the context of inter-species and inter-strain DNA sharing, mainly since it can be easily detected through homology comparisons in bacterial sequences. DNA exchange within the same population or strain is harder to detect as density of polymorphism is low, though theoretical and experimental works suggest it has an important role in adaptation and speciation. This mechanism allows for generation of genetic variability, or can help reduce deleterious variability through ‘repair’ with WT-DNA. It can also, unlike intrinsic mechanisms for genomic variability, relax the adaptational barrier of clonal interference. Here we present an experimental evolution assay, aimed to assess the contribution of natural transformation, and exchange of DNA within the population to the adaptation of B. subtilis. By serially diluting separate lines of naturally competent B. subtilis and a competent deficient derived strain, with and without enhancement of initial standing variation in the populations, we are able to determine that after hundreds of generations of serial dilution regime, the naturally competent lines utilized initial variation in the population and adapted better than the competent deficient lines, as determined by growth improvement comparisons. We also aim to present the genomic signature of natural transformation by sequencing the distinct evolved lines and characterizing their mutation patterns, that might suggest a mechanism for the observed effect on adaptation.