Calcium regulation of growth and differentiation in Streptococcus pneumoniae

Abstract

Streptococcus pneumonk requires 0.15 mM-Ca2+ in the medium for optimal growth. Increasing the Ca2+ concentration to 1 mM triggers either a differentiathe state, competence for genetic transformation during exponential growth, or partial lysis as won as the cultures enter stationary phase. Genetic and physiological data both suggest that these responses are under the control of activator@), excreted in the presence of high Ca2+ concentrations. 45Ca2+ transport is also stimulated by the activator(s). The amiloride derivative 2',4-dimethylbenzarnil (DMB) inhibits 45Ca2+ transport and prevents lysis and competence development. This provides evidence in favour of the involvement of Ca2+ transport in competence and culture lysis. On the other hand, addition of DNA to a competent culture prevents lysis of wild-type bacteria while a mutant, defective for DNA uptake, is not protected from lysis by exogenous DNA. An hypothesis is proposed for competence induction as a global metabolic response to Ca2+, under the control of competence factor.

LuxS impacts on LytA-dependent autolysis and on competence in Streptococcus pneumoniae

“…4A, B). It has been extensively reported that the muramidase encoded by lytA represents the major autolytic function in S. pneumoniae under these experimental conditions (Lopez et al, 1997;Trombe et al, 1992). LuxSdependent autolysis was indeed suppressed by the lytA : : ery mutation, showing that LuxS activity prevents LytAdependent autolysis and contributes to cellular integrity during stasis (Fig.…”

“…Autolysis has classically been described in stationary-phase cultures, and depends on parameters such as the initial pH of the growth medium and its calcium concentration (Trombe et al 1992). It is related to competence development (Peterson et al, 2000;Trombe et al 1992). Recently, LytA-dependent autolysis of exponential cultures has been described in StkP-deficient mutant strains grown at alkaline pH (M.-C. Trombe & S. Romao, unpublished data).…”

“…Control of LytA-dependent autolysis is also a complex process (Severin et al, 1997;Lopez et al, 1997). Autolysis has classically been described in stationary-phase cultures, and depends on parameters such as the initial pH of the growth medium and its calcium concentration (Trombe et al 1992). It is related to competence development (Peterson et al, 2000;Trombe et al 1992).…”

“…Bacterial growth and autolysis were evaluated by measurement of OD 400 of cultures in CAT medium (Trombe et al, 1992) at 37 uC and at the indicated pH. For complementation studies, BSA fraction V was used at the indicated concentration.…”

“…Streptococcus pneumoniae RX isogenic derivatives were routinely used (Table 1). Stock cultures were obtained in casein tryptone medium (CAT) and the cultures were stored at 280 uC after addition of 12 % (v/v) glycerol, as described previously (Trombe et al, 1992). For competence development, CAT medium was complemented by BSA (0?4 %, w/v) and CaCl 2 (0?1 mM), and the pH was adjusted to 8 to make CTM (CAT transformation medium) (Morrison et al, 1984).…”