Identification and Characterization of a New Quorum-Quenching N-acyl Homoserine Lactonase in the Plant Pathogen .

Quorum quenching (QQ) is the ability to interfere with bacterial cell to cell communication, known as quorum sensing (QS). QQ enzymes that degrade or modify acyl homoserine lactones (AHLs) have been attracting increasing interest as promising agents for inhibiting QS-mediated bacterial pathogenicity. Plant pathogens from the genus cause diseases in several economically important crops. Fire blight is a devastating plant disease caused by , affecting a wide range of host species within the Rosaceae and posing a major global threat for commercial apple and pear production. While QS has been described in species, no AHL-degrading enzymes were identified and characterized. Here, phylogenetic analysis and structural modeling were applied to identify an AHL lactonase in (dubbed EaAiiA). Following recombinant expression and purification, the enzyme was biochemically characterized. EaAiiA lactonase activity was dependent on metal ions and effectively degraded AHLs with high catalytic efficiency. Its highest specific activity (/K value) was observed against one of the AHLs (3-oxo-C6homoserine lactone) secreted from . Exogenous addition of the purified enzyme to cultures of reduced the formation of levan, a QS-regulated virulence factor, by 40% and the transcription level of the levansucrase-encoding gene by 55%. Furthermore, preincubation of cultures with EaAiiA inhibited the progress of fire blight symptoms in immature fruits. These results demonstrate the ability of the identified enzyme from to act as a quorum-quenching lactonase.