To investigate quorum sensing in rhizosphere soil, a whole-cell biosensor, Agrobacterium tumefaciens(pAHL-Ice), was constructed. The biosensor responded to all N-acyl homoserine lactones (AHLs) tested, except C(4) homoserine lactone, with a minimum detection limit of 10(-12) M, as well as to both exogenously added AHLs and AHL-producing bacterial strains in soil. This highly sensitive biosensor...