Quorum Sensing in Pseudomonas savastanoi pv. savastanoi and Erwinia toletana: Role in Virulence and Interspecies Interactions in the Olive Knot.

The olive knot disease ( L.) is caused by the bacterium pv. savastanoi. pv. savastanoi in the olive knot undergoes interspecies interactions with the harmless endophyte ; pv. savastanoi and colocalize and form a stable community, resulting in a more aggressive disease. pv. savastanoi and produce the same type of the -acylhomoserine lactone (AHL) quorum sensing (QS) signal, and they share AHLs In this work, we have further studied the AHL QS systems of pv. savastanoi and in order to determine possible molecular mechanism(s) involved in this bacterial interspecies interaction/cooperation. The AHL QS regulons of pv. savastanoi and were determined, allowing the identification of several QS-regulated genes. Surprisingly, the pv. savastanoi QS regulon consisted of only a few loci whereas in many putative metabolic genes were regulated by QS, among which are several involved in carbohydrate metabolism. One of these loci was the aldolase-encoding gene , which was found to be essential for both colocalization of pv. savastanoi and cells inside olive knots as well as knot development. This study further highlighted that pathogens can cooperate with commensal members of the plant microbiome. This is a report on studies of the quorum sensing (QS) systems of the olive knot pathogen pv. savastanoi and olive knot cooperator These two bacterial species form a stable community in the olive knot, share QS signals, and cooperate, resulting in a more aggressive disease. In this work we further studied the QS systems by determining their regulons as well as by studying QS-regulated genes which might play a role in this cooperation. This represents a unique interspecies bacterial virulence model and highlights the importance of bacterial interspecies interaction in disease.