Molecular signals in Pseudomonas tolaasii/Pleurotus eryngii host/pathogen interactions;

P. tolaasii strain P12 has been found in association with brown blotch disease on Pleurotus eryngii, one of the more extensively cultivated mushrooms in the Mediterranean area. Bacterial population density represents a key factor as the infected basidiocarps develop disease symptoms when the pathogen concentration is higher than 104 cfu/g d.w. Virulence of P. tolaasii, mainly due to tolaasin production, may be regulated by quorum sensing (QS) cell-density-dependent regulatory mechanism related to N-acyl homoserine lactones (AHLs). The capacity of P12 to produce AHLs has been investigated. Very low signals related to the production of AHLs were obtained in P12 and other five P. tolaasii strains. Moreover, the capacity to enter the viable but not culturable (VBNC) state was observed under low nutrient anaerobic conditions. As in others bacteria the ability to enter the VBNC state has been associated to the production of QS signals, the above conditions were adopted for QS signal production experiments. Data obtained suggest that specific conditions must be needed to activate QS genes in P12. The involvement of these specific factors in the occurrence of the disease has to be elucidated.