Degradation of N-acylhomoserine Lactone Quorum-sensing Signals by Azorhizobium caulinodans, a Stem Nodule-forming Symbiont in Sesbania rostrata

Abstract

Azorhizobium caulinodans is a nitrogen-fixing bacterium that forms stem and root nodules on Sesbania rostrata. All tested A. caulinodans strains exhibited degradation activity against the quorum-sensing signaling compounds, N-acyl-l-homoserine lactones (AHL). The AHL-degrading gene homolog, attM, was identified in the genome sequences of A. caulinodans MAFF 210031^T and other A. caulinodans strains. Recombinant AttM functions as an AHL lactonase that hydrolyzes the lactone bond of AHL and retains its stable activity at environmental temperatures. The AHL-degrading activity of the attM-deletion mutant was completely diminished, which revealed that AHL degradation by MAFF 210031 was dependent on attM.