Distribution and Characterization of the Novel Quorum-quenching Enzyme AiiB in <i>Priestia megaterium</i> Isolated from a Natural Environment

Many plant pathogenic bacteria regulate the expression of virulence factors via N-acylhomoserine lactone (AHL), a quorum-sensing signaling compound. When numerous spore-forming bacteria were isolated from a natural environment, Priestia megaterium was the dominant species, and some P. megaterium strains exhibited AHL-degrading activity. The results of a HPLC ana-lysis of AHL degradation products demonstrated that P. megaterium degraded AHL by AHL lactonase, which hydrolyzes the lactone ring of AHL. The novel AHL lactonase gene, aiiB, was found in the whole genome sequence of AHL-degrading P. megaterium. The relationship between the presence of aiiB and AHL-degrading activity in P. megaterium strains revealed that P. megaterium may be classified into three AHL degradation groups: Group 1 (with AHL-degrading activity and aiiB), Group 2 (with neither AHL-degrading activity nor aiiB), and Group 3 (without AHL-degrading activity, but with aiiB). A comparative genome ana-lysis suggested that aiiB was obtained or missed by a non-transpositional event during the process of evolution in P. megaterium. The amino acid sequences of AiiB in Group 1 and 3 strains were almost identical, and Escherichia coli harboring aiiB from Groups 1 and 3 exhibited high AHL-degrading activity. Although the AHL-degrading activity of Group 3 strains was markedly weaker than that of Group 1 strains, they degraded AHL in a long-term incubation. Based on the present results, Group 1 and 3 strains, the genomes of which contain aiiB, may reduce potato maceration activity under the control of AHL-mediated quorum sensing in P. carotovorum subsp. carotovorum NBRC 12380.