When assaying for competence related phenotypes in the two other biofilm models, the effects of quorum sensing were different. The second microtiter biofilm model, more frequently used in pneumococcal research, relies on incubation of high numbers of stationary-phase cells

[24]. In this model, the addition of synthetic CSP was not a necessary, however strains unable to synthesize or sense CSP were found to attach to a lower extent the surface compared to the wt. By microscopic analysis we verified that this phenotype was not due to a reduction in the number of single NCT-501 manufacturer attached Trichostatin A molecular weight cells, but it was due to a reduction in number and size of surface attached microbial aggregates. Microcolony formation, already described as an important phenotype in pneumococcal biofilm [7, 15, 24], could be restored in comC mutant strains by addition of synthetic CSP to levels similar to wt strains. The fact that none of the well known genes directly or indirectly regulated by competence has a direct link to attachment of biofilm underlines that effects seen in planktonic exponentially

growing competent cells differ from the biofilm stabilisation phenotype seen here [36]. There DNA Damage inhibitor are parallelisms between our findings and recent work in S. mutans where biofilm formation was also linked to the ComCDE system [37], although if genomic and genetic data indicate that the S. mutans ComDE is orthologous to the S.

pneumoniae BlpRH system and does not directly control transformation [33, 38]. Competence quorum sensing defects in S. mutans were found to determine reduction in biofilm biomass, and addition of CSP partially restored wt biofilm architecture [39]. aminophylline In contrast to S. pneumoniae these ComCD-dependent phenotypes were correlated to the initial stages of biofilm development [39]. Biofilm microcolonies are examples of non-homogeneous microbial populations. In this context, our data indicate a significant effect of the competence quorum sensing system on the capacity of pneumococci to form these aggregates. Such aggregation behaviour in a non-homogeneous population is consistent with the observed clumping in a mixture of competent and non-competent cells which depends on the release of DNA into the medium [40, 41]. Correlation of competence, cell clumping and DNA release fit well with the presence of DNA in the extracellular matrix of attached pneumococci and to subsequent sensitivity of pneumococcal biofilm to DNAse [23, 24]. The release of DNA into the extracellular matrix through the endogenous CSP pathway has also been described to have a significant impact on biofilm biomass in S. mutans [42]. We lack a precise molecular characterisation of the events and we cannot exclude that some of the effects may be indirect and determined through an unknown regulatory pathway.