Metabolic and Genotypic Fingerprinting of Fluorescent Pseudomonads Associated with the Douglas Fir-Laccaria bicolor Mycorrhizosphere

Abstract

A collection of 300 isolates of fluorescent pseudomonads was established 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 assigned 90% of the isolates to the different biovars of Pseudomonas fluorescens, with inverted frequencies of biovars V and I from the bulk soil to the mycorrhizas, suggesting that the mycorrhizas exert a selective stimulation of the P. fluorescens bv. I and a counterselection of the P. fluorescens bv. V present in the soil. Multivariate analyses of the carbon source utilization data led to the definition of homogenous metabolic groups and to the identification of the most discriminating substrates for each group. The isolates from the mycorrhizosphere and from the mycorrhizas seem to preferentially utilize carbohydrates, in particular trehalose, which is the most abundant carbohydrate accumulated in the mycelium of L. bicolor. The results suggest that L. bicolor exerts a trehalose-mediated selection on the fluorescent pseudomonads present in the vicinity of the mycorrhizas. Isolates of P. fluorescens from the mycorrhizosphere and mycorrhizas were then genotypically characterized by restriction fragment length polymorphism of PCR-amplified 16S rRNA genes and enterobacterial repetitive intergenic consensus-PCR DNA fingerprinting. Both methods revealed a high genetic polymorphism within the population studied, which was well correlated with the phenotypic characterization.

Interactions between ectomycorrhizal symbiosis and fluorescent pseudomonads on Acacia holosericea: isolation of mycorrhiza helper bacteria (MHB) from a Soudano-Sahelian soil

“…This result suggests that the MHB are not strictly rhizobacteria. This hypothesis is in accordance with that of Frey-Klett et al [24] who demonstrated that helper bacteria (BBc6) of the mycorrhizal symbiosis between Laccaria bicolor and Douglas ¢r is associated with the mycelium of the fungus in the soil. Moreover, Sen et al [29] have demonstrated that BBc6 was attached to the hyphal wall of L. bicolor in in vitro experiments.…”

“…These results reveal discrepancy with other results obtained with several mycorrhizal plant species such as Douglas ¢r [24], hybrid larch, Sitka spruce [25] and hazel trees mycorrhized with tru¥es [26]. However, in the present study, the soil was sampled just under some Pisolithus fructi¢cations where the yellow mycelial stands of Pisolithus sp.…”

Black truffle‐associated bacterial communities during the development and maturation of Tuber melanosporum ascocarps and putative functional roles

“…Selection of specific bacterial communities by the ectomycorrhizosphere (Frey et al, 1997;Uroz et al, 2007;Izumi and Finlay, 2010) and the mycosphere (i.e. the hyphal network underneath fungal fruiting bodies; Boersma et al, 2009) has been reported for many ectomycorrhizal fungi.…”

The genotypic diversity of Pseudomonas brassicacearum populations isolated from roots of Arabidopsis thaliana: influence of plant genotype

“…However, they failed to ¢nd any relation between ARDRA identi¢cation and biochemical traits (Biolog pro¢les). In contrast, Frey et al [17] evidenced a strict correlation between the ARDRA classi-¢cation and the multivariate analysis of bacterial metabolic ¢ngerprinting for £uorescent pseudomonads isolated from the mycorhizosphere. They also found a close correlation between rep-PCR and metabolic ¢ngerprints.…”

“…This may account for di¡erences observed in rhizobacteria diversity between plant species and between genotypes of the same species [16]. The amount and composition of root exudates are in£uenced by environmental conditions [17,18], and are also under close genetic control [19]. 0168 Arabidopsis thaliana (L.), a small £owering plant of the Brassicaceae family, has been chosen as a`model organism' for molecular genetics of £owering plants and for study of plant^microbe interactions.…”