Hydrogen Peroxide-Dependent DNA Release and Transfer of Antibiotic Resistance Genes in Streptococcus gordonii

Certain oral streptococci produce H2 O2 under aerobic growth conditions to inhibit competing species likeStreptococcus mutans . Additionally, H2 O2 production causes the release of extracellular DNA (eDNA). eDNA can participate in several important functions: biofilm formation and cell-cell aggregation are supported by eDNA, while eDNA can serve as a nutrient and as an antimicrobial agent by chelating essential cations. eDNA contains DNA fragments of a size that has the potential to transfer genomic information. By usingStreptococcus gordonii as a model organism for streptococcal H2 O2 production, H2 O2 -dependent eDNA release was further investigated. Under defined growth conditions, the eDNA release process was shown to be entirely dependent on H2 O2 . Chromosomal DNA damage seems to be the intrinsic signal for the release, although only actively growing cells were proficient eDNA donors. Interestingly, the process of eDNA production was found to be coupled with the induction of theS. gordonii natural competence system. Consequently, the production of H2 O2 triggered the transfer of antibiotic resistance genes. These results suggest that H2 O2 is potentially much more than a simple toxic metabolic by-product; rather, its production could serve as an important environmental signal that facilitates species evolution by transfer of genetic information and an increase in the mutation rate.