title: Acidic stress induces autolysis by a CSP-independent ComE pathway in Streptococcus pneumoniae.
abstract: In Streptococcus pneumoniae, autolysis is considered a programmed cell-death process executed principally by the major autolysin (LytA), and the underlying mechanism causing its activation is not completely understood. It is known that autolysis is triggered by competence development at alkaline pH and regulated by a two-component system, ComDE, which senses a competence-stimulating peptide (CSP) and behaves as a quorum-sensing mechanism. In this work, we found that acidic stress triggered a LytA-mediated autolysis and, curiously, this phenomenon was regulated by a CSP-independent ComE pathway. A further analysis of a hyperactive ComD mutant revealed that ComE needs to be phosphorylated to activate acidic stress-induced lysis (ASIL). The comE transcripts were induced by acidic culture conditions, suggesting that ComE could be sensing acidic stress. We also investigated CiaRH, a two-component system whose null mutants show a comE derepression and a CSP-dependent autolysis induction at alkaline pH. By analysis of cia comE double mutants, we demonstrated that CiaRH protected cells from ASIL by a ComE-independent pathway. Here, we propose that ComE is the principal route of the signalling pathway that determines a global stress response, and clearly regulates the induction of the LytA-mediated programmed cell death in S. pneumoniae. Acidic stress may represent for S. pneumoniae an alternative condition, in addition to competence and antibiotics, to assure the release of virulence factors, DNA and cell-wall compounds by autolysis, favouring genetic exchange and contributing to its pathogenesis.
authors.affiliation: Departamento de Bioquímica Clínica-CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Medina Allende y Haya de la Torre, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: Germán E
authors.initials: GE
authors.lastname: Piñas
authors.affiliation: Departamento de Bioquímica Clínica-CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Medina Allende y Haya de la Torre, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: Paulo R
authors.initials: PR
authors.lastname: Cortes
authors.affiliation: Departamento de Bioquímica Clínica-CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Medina Allende y Haya de la Torre, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: Andrea G Albarracín
authors.initials: AGA
authors.lastname: Orio
authors.affiliation: Departamento de Bioquímica Clínica-CIBICI (CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Medina Allende y Haya de la Torre, Ciudad Universitaria, X5000HUA Córdoba, Argentina.
authors.forename: José
authors.initials: J
authors.lastname: Echenique
mesh_terms: D000143:Acids / Q000494:pharmacology*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001433:Bacteriolysis; D017353:Gene Deletion; D020869:Gene Expression Profiling; D010766:Phosphorylation; D011494:Protein Kinases / Q000235:genetics; D012329:RNA, Bacterial / Q000096:biosynthesis; D012333:RNA, Messenger / Q000096:biosynthesis; D013296:Streptococcus pneumoniae / Q000187:drug effects*
chemical_list: D000143:Acids; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; C103179:ComE protein, Streptococcus pneumoniae; D012329:RNA, Bacterial; D012333:RNA, Messenger; D011494:Protein Kinases; C088910:CiaR protein, Streptococcus pneumoniae