Reciprocal Capsular Transformations of Pneumococci

Abstract

One of the interesting questions concerning bacterial trainsformations is the fate of the endogenous deoxyribonucleic acid (DNA) present in the host bacterium about to produce genetically transformed progeny as a consequence of infection by an exogenous DNA agent. When a bacterium is genetically transformed, a novel DNA ageint is not simply acquired, but a homologous DNA agent previously present in the cell is effectively removed. This replacement of one agent, the eiidogenous factor, by an infectious agent homologous to it is demonstrated in reciprocal transformations. The first example of the reversibilitv of transformation was given by

Population genomics of hypervirulentKlebsiella pneumoniaeclonal group 23 reveals early emergence and rapid global dissemination

“…These may include the hyper-expression of K1 capsule, which may provide a physical barrier against transformation and conjugation and also CRISPR/Cas systems, which defend against foreign DNA that does manage to penetrate the cell. The significant association between upregulated capsule production and reduced uptake of DNA has previously been documented in Streptococcus pneumoniae 65 . Notably, these mechanisms could also explain the lack of homologous recombination in CG23, which is common in other clonal groups 66,67 .…”

Regulation of competence for genetic transformation in Streptococcus pneumoniae

“…The results presented here clearly demonstrate that neither transcription factor which would in turn activate expression of the com genes, much as ComK does in B. subtilis (van Ami nor any of the three highly homologous oligopeptide- Sinderen et al 1995). Neither a two-component regulator that triple mutant cells are more resistant than wild type to trypsin treatment (G. Alloing and J.-P. Claverys, unpub-that could act as a receptor for CSP nor a competence-specific transcription factor have been identified thus far.…”

“…suggested that AliA plays some role in the modulation of competence. Interestingly, we observed that CP strains, In addition to developing competence in the presence of trypsin, mutant cells become competent when grown as dilute which are derived from strain Rx (Ravin 1959), are naturally aliA − due to a deletion of the 5? moiety of the gene (G. cultures.…”

Immune-protective antibodies against capsular polysaccharides do not affect natural competence of Streptococcus pneumoniae: implications for current conjugate vaccination strategies?

“…Increased expression of capsular polysaccharide results in a lower degree of competence [15,18], whereby the capsule acts as a barrier that prevents competence factor from reaching its cellular target [20]. We hypothesize that opsonization may increase the steric hindrance by the capsule.…”