Quorum Sensing in the Soft-Rot Erwinias

Abstract

One of the first bacterial species for which N-acylhomoserine lactone (AHL) quorum sensing (QS) was described was Erwinia carotovora. Since then, QS has been well studied in the soft-rot erwinias, where, as described in this chapter, QS plays a key role in the regulation of secreted plant cell wall-degrading enzymes (PCWDEs) production and hence in virulence. In certain strains, a well-defined AHL QS system also controls production of β-lactam antibiotic, carbapenem. In addition, it must be emphasized that QS is only one of many regulatory inputs into virulence factor production in Erwinia. The majority of the key secreted virulence factors of E. carotovora and E. chrysanthemi, including multiple Pels, Peh, Cel, and Svx, are secreted by a type II secretion system known as the Out system. There have been two reports describing the existence of AHL QS in E. amylovora. First, production of a single AHL, most likely 3-oxo-C6-HSL, was described for several Italian strains of E. amylovora; for one strain, production of AHL was observed in planta. Second, AHL activity was detected in the culture supernatant of a Swiss strain of E. amylovora. Both reports describe the detection and partial sequencing of pairs of convergent luxIR homologues, named eamIR.