A novel biosensor strain ( ALM403) that responded to -acyl homoserine lactone (AHL) was constructed using a cassette as a regulatory sequence and beta-mannanase as a reporter gene. Dinitrosalicylic acid method was used to detect the response of the sensor strain to -acyl homoserine lactone. By investigating the response to a range of concentrations of beta-oxooctanoyl--homoserine lactone (OOHL), it was demonstrated that the expression of mannanase in ALM403 could be greatly enhanced by OOHL and resulted in an assayable phenotype. A high-throughput screening approach was developed to isolate AHL-degrading microorganisms, and a marine sp. S66-4 showing a marked AHL-degrading ability was successfully isolated. In conclusion, the bioassay system provided a simple and efficient approach to isolate AHL-degrading bacteria.