Methods:Aliquots of mid-log phase bacteria were spot plated (n=9) and exposed to oxygen stress, which damages DNA, or heat stress, which damages the outer membrane. All plates were then incubated anaerobically to allow recovery. Viable cells were quantified to calculate and compare (t-test, p<0.05) survival rates between the test and control groups.
Results: Oxygen exposure presented a significant drop in the viability of the mutant strains as opposed to the wild-type. In contrast, heat exposure did not result in a significant loss of viability for any of the strains tested. The survival rates of comF and recA mutants did not demonstrate any statistically significant differences between the two in any of the assays.
Conclusions: Our results support that the hypothesis that the comF-recA system of exogenous DNA uptake and genomic integration is important for survival during immediate stresses that damage DNA, in addition to its role in long-term adaptation to the host. The similar sensitivity of the mutant strains to stressors suggests that both genes are comparably involved and necessary in the maintenance of viability in an environment as harsh as the oral cavity. Further studies should investigate the robustness of this mechanism through the application of other DNA- and non-DNA-damaging stressors beyond oxygen and heat shock.