METABOLIC AND GENOTYPIC FINGERPRINTING OF FLUORESCENT PSEUDOMONADS ASSOCIATED WITH THE DOUGLAS-FIR LACCARIA BICOLOR MYCORRHIZOSPHERE

A collection of 300 isolates of fluorescent pseudomonads was establish ed from Douglas fir-Laccaria bicolor mycorrhizas and mycorrhizosphere and from adjacent bulk soil, These isolates were first phenotypically characterized with the Biolog method. Taxonomic identification assigne d 90% of the isolates to the different biovars of Pseudomonas fluoresc ens, with inverted frequencies of biovars V and I from the bulk soil t o the mycorrhizas, suggesting that the mycorrhizas exert a selective s timulation of the P. fluorescens by, I and a counterselection of the P . fluorescens by. V present in the soil, Multivariate analyses of the carbon source utilization data led to the definition of homogeneous me tabolic groups and to the identification of the most discriminating su bstrates for each group, The isolates from the mycorrhizosphere and Be nt the mycorrhizas seem to preferentially utilize carbohydrates, in pa rticular trehalose, which is the most abundant carbohydrate accumulate d in the mycelium of L. bicolor. The results suggest that L. bicolor e xerts a trehalose-mediated selection on the fluorescent pseudomonads p resent in the vicinity of the mycorrhizas. isolates of P. fluorescens from the mycorrhizosphere and mycorrhizas were then genotypically char acterized bg restriction fragment length polymorphism of PCR-amplified 16S rRNA genes and enterobacterial repetitive intergenic consensus-PC R DNA fingerprinting. Both methods revealed a high genetic polymorphis m within the population studied, which was well correlated with the ph enotypic characterization.