The luxS Gene Is Involved in AI-2 Production, Pathogenicity, and Some Phenotypes in Erwinia amylovora

Erwinia amylovora causes fire blight of apple, pear, and other members of the Rosaceae family. The enzyme LuxS catalyzes the last step in the production of autoinducer-2 (AI-2), a molecule implicated with quorum sensing in many bacterial species. It is now well recognized that LuxS also plays a central role in sulfur metabolism and in the activated methyl cycle, which is responsible for the generation of S-adenosyl-L-methionine. A research paper has reported that luxS is not involved with quorum sensing in Er. amylovora, but in our study, Er. amylovora strain NCPPB1665 (Ea1665) produced luxS-dependent extracellular AI-2 activity. Additionally, the maximal AI-2 activity occurred during late-exponential and early-stationary growth phases and diminished during the stationary phase. The luxS mutant of Ea1665 was constructed, and the phenotypes of a defined luxS mutant have been characterized. Inactivation of luxS in Ea1665 impaired motility, extracellular polysaccharide (EPS) production, and tolerance for hydrogen peroxide, and reduced virulence on pear leaves.