P683 HYDROLYTIC ENZYMES AND BIOACTIVE SECONDARY METABOLITES IN BURKHOLDERIA GLADIOLI PV. AGARICICOLA ARE QUORUM SENSING REGULATED AND APPEAR TO HAVE A ROLE IN THE PATHOGEN VIRULENCE ON AGARICUS BISPORUS Daniela Lamorte§1, Hazem S. Elshafie§1,2, Giulia Devescovi3, Pietro Lo Cantore1, Sabino Bufo2, Vittorio Venturi3, Nicola Sante Iacobellis1 1Scuola di Scienze Agrarie, Forestali, Alimentari ed Ambientali 2Dipartimento di Scienze, Università degli Studi della Basilicata, Viale dell’Ateneo Lucano, 85100, Potenza, Italy 3The International Centre for Genetic Engineering and Biotechnology, Area Science Park Padriciano 99, 34149 Trieste, Italy e-mail: email@example.com Recent studies showed that strains of Burkholderia gladioli pv. agaricicola (Bga), the causal agent of the soft rot of several cultivated mushroom species, produce an array of N-Acyl homoserine lactones (AHLs) which may be expected to regulate some biological activities possibly involved in the mushroom-pathogen interaction. In this study AHLdeficient mutants of four virulent strains of Bga were constructed by allelic exchange and tested for various phenotypes including (i) antibacterial activity against Bacillus megaterium and Escherichia coli, (ii) production of antimicrobial and haemolytic substances, (iii) chitinase, protease and glucanase activities and (iv) virulence on Agaricus bisporus pseudo-tissues blocks and whole basidiomes. AHLs-deficient mutants showed a significant reduction in antibacterial activity and virulence on A. bisporus pseudo-tissues blocks and whole basidiomes, the lack of the haemolytic, an also the reduction of chitinolytic, proteolytic and glucanolytic activities. Culture extracts of the mutants showed low antimicrobial activity against B. megaterium and E. coli and the lack of haemolytic activities when compared to the parental strains. HPLC analysis of the culture extracts confirmed the absence/lower level of the typical bioactive substances present in the parental strains chromatograms. These results suggest the important role of Quorum Sensing, mediated by AHLs, in the regulation of the above traits which are mostly likely important in the pathogen virulence.