Natural genetic transformation is a mechanism of horizontal DNA transfer that promotes the shuffling of genetic information in bacteria by homologous recombination. In this work conducted in Streptococcus pneumoniae (pneumococcus), a major opportunistic pathogen of humans, Calum Johnston, Rachel Hope, Anne-Lise Soulet, Marie Dewailly, David De Lemos and Patrice Polard (LMGM-CBI) visualised in real time by fluorescence microscopy the initiation of DNA integration into the genome during transformation and thus revealed that DNA recombination is specifically initiated on the replication forks of the genome.
Figure : The RecA nucleofilaments of the homologous recombination mechanism of the pneumococcal genetic transformation DNA assemble via the action of the DprA protein on the genome replication forks.
Fluorescence microscopy images show colocalisation between DprA and the genome replication machinery, as well as a RecA filament that emanates from colocalisation with the same replication machinery. The right-hand side of the figure shows the pathway of DNA transferred into the cell during transformation: exogenous DNA internalised as single-stranded DNA is taken up by the combined action of DprA and RecA to generate the RecA nucleofilament on the replication forks of the genome that initiates recombination, thus ideally accessing the genome for the search for a complementary sequence
The RecA-directed recombination pathway of natural transformation initiates at chromosomal replication forks in the pneumococcus.
Johnston CHG, Hope R, Soulet AL, Dewailly M, De Lemos D, Polard P., PNAS, 2023, Feb.doi: 10.1073/pnas.2213867120
Contact : Patrice Polard