AmiE, a Novel N -Acylhomoserine Lactone Acylase Belonging to the Amidase Family, from the Activated-Sludge Isolate Acinetobacter sp. Strain Ooi24

Many Gram-negative bacteria useN -acyl-l -homoserine lactones (AHLs) as quorum-sensing signal molecules. We have reported thatAcinetobacter strains isolated from activated sludge have AHL-degrading activity. In this study, we cloned theamiE gene as an AHL-degradative gene from the genomic library ofAcinetobacter sp. strain Ooi24. High-performance liquid chromatography analysis revealed that AmiE functions as an AHL acylase, which hydrolyzes the amide bond of AHL. AmiE showed a high level of degrading activity against AHLs with long acyl chains but no activity against AHLs with acyl chains shorter than eight carbons. AmiE showed homology with a member of the amidases (EC 3.5.1.4) but not with any known AHL acylase enzymes. An amino acid sequence of AmiE from Ooi24 showed greater than 99% identities with uncharacterized proteins fromAcinetobacter ursingii CIP 107286 andAcinetobacter sp. strain CIP 102129, but it was not found in the draft or complete genome sequences of otherAcinetobacter strains. The presence of transposase-like genes around theamiE genes of these threeAcinetobacter strains suggests thatamiE is transferred by a putative transposon. Furthermore, the expression of AmiE inPseudomonas aeruginosa PAO1 reduced AHL accumulation and elastase activity, which were regulated by AHL-mediated quorum sensing.