Modulation of Competence for Genetic Transformation in Streptococcus pneumoniae

Abstract

The spontaneous development of competence by cultures of Streptococcus pneumoniae in casein hydrolysate medium was strongly dependent on the initial pH of the culture medium. Cells growing in cultures beginning with a wide range of initial pH values (6-8 to 8.0) all developed competence, as measured by [3H]DNA uptake, [ 3H]DNA degradation and genetic transformation; but the initial pH of the medium affected both the timing of the occurrence of competence and the number of times the culture became competent. In cultures grown in media of lower initial pH, competence occurred only once, at high population densities, while in more alkaline media a succession of competence cycles occurred, beginning at lower cell densities. The critical population density required for the initiation of competence varied tenfold over the pH range studied. Successive competence cycles in an alkaline medium were not equivalent: while the percentage of competent cells in the first competence cycle was high (approximately 80%), that in the second competence cycle was lower (approximately 12%). Correspondingly, competence-specific proteins were less prominent in the labelled-protein pattern of the second competence cycle than in that of the first. These features of the physiology of competence control make it possible to adjust the expression of competence to suit various experimental requirements.

Calcium regulation of growth and differentiation in Streptococcus pneumoniae

“…CF might be a molecule allowing a cycle of consecutive lysis and transformations, resulting in cross-feeding within natural co-cult ivated su bpopulations. Indeed, under laboratory conditions, successive competence waves can be observed in the same culture (Chen & Morrison, 1987). Genetic exchanges at competence might be part of a more general cross-feeding event.…”

“…In cultures growing at neutral pH, competence develops naturally in the late exponential phase and at high cell density (Chen & Morrison, 1987). It was possible to induce competence in the early exponential phase, at neutral pH, by the addition of extra CF, above the concentration which induced competence in alkaline cultures (Fig.…”

“…In the experimental system used for this study, competence was induced in early exponential phase when the culture was alkaline, as described by Chen & Morrison (1987). A competence cycle could be divided into two steps: induction, which required 20 min incubation at 37 "C in CF-containing medium or 60 to 120 min in the absence of CF, and expression, where all the properties of the competent bacteria were expressed.…”

Signal diffusion and the mitigation of social exploitation in pneumococcal competence signalling

“…Competence induction with decreasing diffusivity Natural competence in S. pneumoniae is induced when the concentration of the secreted peptide, CSP, exceeds a threshold level of approximately 10 ng ml 21 (Havarstein et al 1995), which is reached at a cell density of approximately 10 8 cells ml 21 (although this varies across laboratories and media types (Chen & Morrison 1987). The competent state arises rapidly within the pneumococcal population and then declines.…”

Regulation of competence for genetic transformation in Streptococcus pneumoniae

“…oralis chromosomal a second wave of competence followed the first between one DNA as donor (Fenoll et al 1994). It is tempting to speculate and two generations later (Chen and Morrison 1987). The that transformation has also played a role in the evolution of active removal of circulating CSP via the oligopeptide binding more than 90 different capsular types that have been reported lipoproteins AmiA, AliA and AliB could contribrute to the for Strep.…”