E. Azoulaydupuis et al., PLEIOTROPIC MUTATIONS ALTER THE KINETICS OF CALCIUM-TRANSPORT, COMPETENCE REGULATION, AUTOLYSIS AND EXPERIMENTAL VIRULENCE IN STREPTOCOCCUS-PNEUMONIAE, Research in microbiology, 149(1), 1998, pp. 5-13
Streptococcus pneumoniae is a pathogen in which the extracellular calc
ium concentration plays a major physiological role, in growth as well
as in the induction of competence for genetic transformation and activ
ation of autolysis. Both responses are under the control of a protein
activator exported in the medium. We have checked the impact of mutati
ons which alter the regulation of competence and autolysis on experime
ntal virulence. Isogenic encapsulated derivatives carrying the relevan
t mutations were serotype 3 smooth clones, obtained by transformation
of the relevant rough strains with DNA from a serotype 3 smooth isolat
e. Survival kinetics and bacterial clearance from the blood were follo
wed after intraperitoneal infection of Swiss mice with the different b
acterial cultures. In this model, mutants showing an attenuation of vi
rulence relative to the wild type fell into two classes. In the first,
represented by the lytA::ery mutant V1095 defective for calcium-induc
ed autolysis, attenuated virulence could be correlated with rapid bact
erial clearance from the blood. In the second, represented by the dmb
mutants V2200 and V3300, attenuation was associated with delayed bacte
rial clearance from the blood, and correlated with altered kinetics of
calcium transport and of regulation of competence and autolysis. It a
ppeared unlikely that attenuation of virulence for strains V2200 and V
3300 was a direct consequence of their competence phenotype, since the
com::ery mutants V1008 and V1019, defective for the production of the
competence activator, were as virulent as the wild-type strain. Autol
ysis involving an N-acetyl-muramyl-alanine amidase encoded by lytA was
also regulated by calcium. The inserted allele lytA0::ery further red
uced virulence in the dmb1 background (V2200). This additive effect of
lytA(-) to dmb1 points to different routes of virulence regulation by
LYT and DMB1 and suggests that the kinetics of calcium traffic contro
ls several pathways involved in the virulence of pneumococcus.