The Effect of Quorum Quenching Bacteria on Pathogenicity of Pectobacterium carotovorum Causal Agent of Potato Soft Rot

Pectobacterium carotovorum is one of the most important bacterial pathogens of potato in the world.The expression of numerous genes including those involved in the production of virulence determinants in this bacterium are regulated by quorum sensing (QS). The signal molecules involved in QS in P. carotovorum belong to the group of N-acyl homoserine lactones (AHLs). Recently, several soil bacteria were found to degrade AHLs, thereby interfering with the QS system. In this research, 1280 bacterial strains were isolated from potato rhizosphere in Iran. For the screening of isolates for AHL-inactivating, Chromobacterium violaceum CV026 and Escherchia coli pSB401 was used as biosensors. The 69 isolates have highly AHL-degrading potential. The AHL degradation measurement by HPLC showed that residue of C6-HSL was not detected in some isolates that means completely degradation of it by antagonists. The screened isolates tested for protect potato tubers against soft rot. 40 strains reduced tuber soft rot more than 50 percent. 16 of the best isolates were used for inhibition of stem tissue maceration. Bacillus toyoensis 2L, Escherchia coli 1M and Acinetobacter calcoaceticus 32P reduced stem maceration more than 70 percent. These strains were identified by 16s rDNA sequencing. These results showed that interference with P. carotovorum quorum sensing system can be considered as an attractive target for development of biological control method of this disease.