RESUMEN
Various mechanisms exist that enable bacteria to resist bacteriophage infection. Resistance strategies include the abortive infection (Abi) systems, which promote cell death and limit phage replication within a bacterial population. A highly effective 2-gene Abi system from the phytopathogen Erwinia carotovora subspecies atroseptica, designated ToxIN, is described. The ToxIN Abi system also functions as a toxin-antitoxin (TA) pair, with ToxN inhibiting bacterial growth and the tandemly repeated ToxI RNA antitoxin counteracting the toxicity. TA modules are currently divided into 2 classes, protein and RNA antisense. We provide evidence that ToxIN defines an entirely new TA class that functions via a novel protein-RNA mechanism, with analogous systems present in diverse bacteria. Despite the debated role of TA systems, we demonstrate that ToxIN provides viral resistance in a range of bacterial genera against multiple phages. This is the first demonstration of a novel mechanistic class of TA systems and of an Abi system functioning in different bacterial genera, both with implications for the dynamics of phage-bacterial interactions.
Asunto(s)
Antitoxinas/genética , Toxinas Bacterianas/genética , Bacteriófagos/efectos de los fármacos , Pectobacterium carotovorum/genética , Pectobacterium carotovorum/virología , ARN/genética , Secuencia de Bases , Escherichia coli/crecimiento & desarrollo , Datos de Secuencia Molecular , PlásmidosRESUMEN
The bacterial mouse pathogen Citrobacter rodentium causes attaching and effacing (AE) lesions in the same manner as pathogenic Escherichia coli, and is an important model for this mode of pathogenesis. Quorum sensing (QS) involves chemical signalling by bacteria to regulate gene expression in response to cell density. E. coli has never been reported to have N-acylhomoserine lactone (AHL) QS, but it does utilize luxS-dependent signalling. We found production of AHL QS signalling molecules by an AE pathogen, C. rodentium. AHL QS is directed by the croIR locus and a croI mutant is affected in its surface attachment, although not in Type III secretion. AHL QS has an important role in virulence in the mouse as, unexpectedly, the QS mutant is hypervirulent; by contrast, we detected no impact of luxS inactivation. Further study of QS in Citrobacter should provide new insights into AE pathogenesis. As the croIR locus might have been horizontally acquired, AHL QS might exist in some strains of pathogenic E. coli.
Asunto(s)
Citrobacter rodentium/patogenicidad , Percepción de Quorum , 4-Butirolactona/análogos & derivados , 4-Butirolactona/biosíntesis , 4-Butirolactona/deficiencia , 4-Butirolactona/genética , Animales , Adhesión Bacteriana/efectos de los fármacos , Cromosomas Bacterianos , Elementos Transponibles de ADN/genética , ADN Bacteriano/genética , Dimetilsulfóxido/farmacología , Femenino , Eliminación de Gen , Regulación Bacteriana de la Expresión Génica , Genes Bacterianos , Prueba de Complementación Genética , Ratones , Ratones Endogámicos C3H , Mutación , Mapeo Físico de Cromosoma , Solventes/farmacología , Organismos Libres de Patógenos Específicos , VirulenciaRESUMEN
A bacteriophage (phiIF3) capable of mediating generalized transduction in Serratia marcescens strain Db11 has been isolated and characterized. The genome of this Serratia strain has recently been sequenced and is likely to become the reference strain for S. marcescens researchers. phiIF3 is most likely a virulent phage, which can transduce markers at frequencies of 10(-6) transductants per p.f.u. It has a lipopolysaccharide receptor and was determined to have a latent period of 50 min and a burst size of approximately 100 phages. The phage DNA was resistant to digestion with restriction enzymes. Electron microscopy showed phiIF3 to be a member of the family Myoviridae. This is the first report of a generalized transducing phage able to infect Db11 and this phage will be a valuable tool for functional genomic analysis of the pathogen host.