9, green dotted
line). The vertical blue line indicates the observed Wallace value in the studied sample. (B) To identify the value of the IPR parameter that is in best agreement with the data, the probability density at the observed Wallace values was computed for simulated populations with varying inter-pherotype recombination probabilities (IPR from 0.1 to 0.9), both for Wallace indexes of sequence type (blue line) and of clonal complex (red line) predicting pherotype. Conclusion In agreement with previous suggestions [14, 20, 21], we propose that the specific ComC/ComD match facilitates a form of assortative genetic exchange, which could maintain genetically diverse subpopulations within this species. Although recent studies addressing the phenomenon of fratricide in pneumococci favor the hypothesis of preferential inter-pherotype genetic exchange [42], the data presented here argues that in natural mTOR inhibitor populations intra-pherotype exchanges prevail, creating a barrier to gene exchange. In vitro studies that led to the fratricide hypothesis show that if two pneumococcal strains with different pherotypes are grown together, the one that becomes competent earlier will have a greater probability of being transformed with DNA from the other strain [42]. In
order to observe the impact of this admixture promoting event in pneumococcal natural populations, frequent and adequate co-colonization events involving different pherotypes must occur. find more On the other hand, fratricide has also been observed in experiments with a single strain [13]. Dynamic bi-stable regulatory systems, as described for Bacillus subtilis [43], may underlie the mechanism leading to the simultaneous
presence of competent and non-competent cells of the same strain or the same pherotype. If natural co-colonization by strains of different pherotypes is rare or inadequate to promote gene exchange, it is possible to reconcile the inter-pherotype fratricide observations with the pherotype defined genetic differentiation identified here. The observed genetic barrier would then be justified if co-colonization events involving different strains of the same pherotype are more frequent or more adequate for recombination, leaving intra-pherotype fratricide and genetic exchange as the most common event in Lumacaftor in vitro natural populations. All the isolates analyzed were recovered in Portugal from invasive infections and it is therefore unlikely that geographic or ecological fragmentation could explain the pattern observed. The model simulations also exclude the possibility that our observation results simply from the structure of the pneumococcal population, with multiple isolates sharing the same genotype or with a recent common ancestry. It would also be plausible to assume that the CSP-2 population was recently established by introduction of a novel pherotype into pneumococci.