Characterization of an adaptive acid-tolerance mechanism in Streptococcus pneumoniae: identification of acid-induced proteins.

CORTES PR; PIÑAS GE; ECHENIQUE J

Bariloche

Congreso; XXXIX Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular,; 2003

SAIB

During the invasion process, S. pneumoniae has to overcome different stress conditions due to host defence mechanisms, like pH decrease produced by phagosomes. The aim of this work was to study a putative acid tolerance response (ATR) in pneumococcus. We found that log- phase cells, grown previously at neutral pH, survived 2 hours at pH 4.4. In contrast, stationary-phase cells required a pre-incubation in an acetate-bufferized medium at pH 5.6 during 1 h at 37oC to tolerate this pH condition. With the purpose to study the cellular density effect on ATR induction, we analysed comE mutants. The comE gene encodes a response regulator that belongs to the quorum-sensing system ComCDE, involved in competence regulation. The null mutant, comE::km, showed no significant effect on ATR, however, the hyperactive mutant comE38KE repressed either acidic or log-phase ATR induction. These results demonstrate that ATR induction is controlled by the ComE pathway. In addition, we searched acidinduced proteins in different proteic fractions obtained by acetone precipitation and urea solubilization. The proteic band patterns were compared by PAGE-SDS, and we found four proteins clearly induced by pH 5.6 (30, 70, 80 and 120 kDa). At present, we identified by peptide sequencing and pneumococcal genome analysis two proteins: an ATP-dependent protease and a fructose aldolase. In the future, we will determine the impact of these genes on ATR induction by mutagenesis assays.