Cosmopolitan distribution of phlD-containing dicotyledonous crop-associated biocontrol pseudomonads of worldwide origin

In biocontrol fluorescent pseudomonads, phlD encodes a polyketide synthase required for the synthesis of the antifungal compound 2,4-diacetylphloroglu cinol (Phl). Here, PCR-restriction fragment length polymorphism analysis wa s used to compare phlD alleles in 77 dicot-associated pseudomonads originat ing from various countries worldwide and 10 counterparts from a monocotyled onous host (wheat). The 16 restriction patterns obtained were mostly unrela ted to geographic location or dicot host, Cluster analysis distinguished ei ght phlD clusters at a similarity level of 0.63. One cluster grouped 18 pse udomonads that produced also the antifungal polyketide pyoluteorin but coul d not assimilate D-galactose, D-galactonate lactone, D-sorbitol, L-arabinos e, D-saccharate or D-xylose. These 18 pseudomonads, along with the eight ps eudomonads from a second phlD cluster, were the only isolates that failed t o deaminase 1-aminocyclopropane-1-carboxylate (ACC), a rare root growth pro motion trait. Overall, assessment of phlD polymorphism, ACC deaminase activ ity and catabolic profiles pointed to a cosmopolitan distribution of Phl-pr oducing biocontrol fluorescent pseudomonads of worldwide origin associated with dicotyledonous crop plants. (C) 2001 Federation of European Microbiolo gical Societies. Published by Elsevier Science B.V.. All rights reserved.