[WCB-10] Direct imaging of horizontal gene transfer in Streptococcus pneumoniae
The rapid spread of antimicrobial resistance and vaccine escape in the important opportunistic human pathogen Streptococcus pneumoniae can be largely attributed to competence-induced transformation, which involves the uptake and assimilation of exogenous DNA. Transforming DNA enters the cell in a single strand can lead to new genotypes. To better understand the single cell dynamics during transformation, we set out fluorescence-based transformation reporter to determine the rate-limiting steps in this process. We show that within isogenic populations, all cells become naturally competent and bind exogenous DNA. Under experimental ideal condition, we find that transformation is highly efficient and that the chromosomal location of the integration site has limited influence on recombination efficiency. Indeed, we have observed simultaneous multiple recombination events in single recipients in real-time. However, because of saturation and because a single-stranded donor DNA replaces the original allele, transformation efficiency has an upper threshold of approximately 50% of the population. The fixed mechanism of the unbiased homeologous recombination during pneumococcal transformation allows for multiple chromosomal integration events and results in a fail-safe strategy for the population as half of the population generally keeps an intact copy of the original genome.