Pectobacterium carotovorum (Pc) causing potato tuber soft rot uses N-acyl-L-homoserine lactones (AHLs) to control the production of virulence factors via quorum sensing (QS). Some bacteria produce enzymes to inactivate the AHL signals of pathogenic bacteria via a phenomenon known as quorum quenching. One hundred bacterial isolates from potato tubers were screened for AHL-degrading activity using biosensor strain Chromobacterium violaceum CV026. Of these isolates, 20 were able to inactivate AHLs from the pathogenic bacteria in vitro. Of the 20 isolates, 6 attenuated tissue maceration of potato tubers by Pc. Suppression of tuber soft rot was observed even when these isolates were applied 24 h after the pathogen was introduced. Their colonization in tubers was approximately 103-104 cfu/g tuber, 7 days after inoculation. These isolates were identified as Bacillus sp., Variovorax sp., Variovorax paradoxus and Agrobacterium tumefaciens. Four of these isolates showed putative AHL-lactonase activity and provided the most significant protection against Pc. Therefore, AHL-degrading endophytic bacteria can be utilized as a novel biocontrol agent of potato tuber soft rot in Vietnam.
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