title: A pore-forming toxin enables Serratia a nonlytic egress from host cells.
abstract: Several pathogens co-opt host intracellular compartments to survive and replicate, and they thereafter disperse progeny to prosper in a new niche. Little is known about strategies displayed by Serratia marcescens to defeat immune responses and disseminate afterwards. Upon invasion of nonphagocytic cells, Serratia multiplies within autophagosome-like vacuoles. These Serratia-containing vacuoles (SeCV) circumvent progression into acidic/degradative compartments, avoiding elimination. In this work, we show that ShlA pore-forming toxin (PFT) commands Serratia escape from invaded cells. While ShlA-dependent, Ca2+local increase was shown in SeCVs tight proximity, intracellular Ca2+sequestration prevented Serratia exit. Accordingly, a Ca2+surge rescued a ShlA-deficient strain exit capacity, demonstrating that Ca2+mobilization is essential for egress. As opposed to wild-type-SeCV, the mutant strain-vacuole was wrapped by actin filaments, showing that ShlA expression rearranges host actin. Moreover, alteration of actin polymerization hindered wild-type Serratia escape, while increased intracellular Ca2+reorganized the mutant strain-SeCV actin distribution, restoring wild-type-SeCV phenotype. Our results demonstrate that, by ShlA expression, Serratia triggers a Ca2+signal that reshapes cytoskeleton dynamics and ends up pushing the SeCV load out of the cell, in an exocytic-like process. These results disclose that PFTs can be engaged in allowing bacteria to exit without compromising host cell integrity.
authors.forename: Gisela
authors.initials: G
authors.lastname: Di Venanzio
authors.forename: Martina
authors.initials: M
authors.lastname: Lazzaro
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Universidad Nacional de Rosario, Rosario, Argentina.
authors.forename: Enrique S
authors.initials: ES
authors.lastname: Morales
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Universidad Nacional de Rosario, Rosario, Argentina.
authors.forename: Darío
authors.initials: D
authors.lastname: Krapf
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario, Consejo Nacional de Investigaciones Científicas y Tecnológicas, Universidad Nacional de Rosario, Rosario, Argentina.
authors.forename: Eleonora
authors.initials: E
authors.lastname: García Véscovi
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002413:Cations, Divalent / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D003599:Cytoskeleton / Q000378:metabolism; D005089:Exocytosis; D006460:Hemolysin Proteins / Q000378:metabolism*; D052899:Pore Forming Cytotoxic Proteins / Q000378:metabolism*; D012706:Serratia marcescens / Q000378:metabolism / Q000502:physiology*; D014617:Vacuoles / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D002413:Cations, Divalent; D006460:Hemolysin Proteins; D052899:Pore Forming Cytotoxic Proteins; C089911:ShlA protein, Serratia marcescens; D002118:Calcium