QUORUM SENSING IN RHIZOBIA ISOLATED FROM THE SPORES OF THE MYCORRHIZAL SYMBIONT RHIZOPHAGUS INTRARADICES. Quorum sensing in rhizobia

This work investigated the occurrence and extent of QS among rhizobia living strictly associated with AMF spores, using two different QS reporter strains, Agrobacterium tumefaciens NTL4 pZRL4 and Chromobacterium violaceum CV026. We also assessed the QQ activity among Bacillus isolates living in the same ecological niche. Most rhizobia were found to be quorum-signalling positive (86%), including six strains producing very high levels of N-acyl homoserine lactones signal molecules (AHLs). The results were confirmed by the microtiter plate assay, which detected 63% of the tested bacteria as medium/high AHLs producers. The 16S rDNA sequence analysis grouped the rhizobia in two clusters, consistent with the QS phenotype. None of the tested Gram-positive bacteria showed QQ activity, able to disrupt the QS signalling, suggesting the absence of antagonism among bacteria living in AMF sporosphere. Our results provide the first evidence of the ability of most AMF-associated rhizobia to communicate through QS, emphasizing the potential importance of such a behaviour in association with key-plant growth-promoting functions, and the complexity of ecological interactions possibly affecting significant functional traits of the symbiosis.