Detection and quantification of a mycorrhization helper bacterium and a mycorrhizal fungus in plant-soil microcosms at different levels of complexity.

Florence Kurth,Lasse Feldhahn,Tesfaye Wubet,Tilmann Weber,Katharina Zeitler,François Buscot,Sylvie Herrmann,Václav Krištůfek,Mika T Tarkka,Thomas R Neu

doi:10.1186/1471-2180-13-205

Abstract

BackgroundHost plant roots, mycorrhizal mycelium and microbes are important and potentially interacting factors shaping the performance of mycorrhization helper bacteria (MHB). We investigated the impact of a soil microbial community on the interaction between the extraradical mycelium of the ectomycorrhizal fungus Piloderma croceum and the MHB Streptomyces sp. AcH 505 in both the presence and the absence of pedunculate oak microcuttings.ResultsSpecific primers were designed to target the internal transcribed spacer of the rDNA and an intergenic region between two protein encoding genes of P. croceum and the intergenic region between the gyrA and gyrB genes of AcH 505. These primers were used to perform real-time PCR with DNA extracted from soil samples. With a sensitivity of 10 genome copies and a linear range of 6 orders of magnitude, these real-time PCR assays enabled the quantification of purified DNA from P. croceum and AcH 505, respectively. In soil microcosms, the fungal PCR signal was not affected by AcH 505 in the absence of the host plant. However, the fungal signal became weaker in the presence of the plant. This decrease was only observed in microbial filtrate amended microcosms. In contrast, the PCR signal of AcH 505 increased in the presence of P. croceum. The increase was not significant in sterile microcosms that contained plant roots.ConclusionsReal-time quantitative PCR assays provide a method for directly detecting and quantifying MHB and mycorrhizal fungi in plant microcosms. Our study indicates that the presence of microorganisms and plant roots can both affect the nature of MHB-fungus interactions, and that mycorrhizal fungi may enhance MHB growth.

Highlights

Host plant roots, mycorrhizal mycelium and microbes are important and potentially interacting factors shaping the performance of mycorrhization helper bacteria (MHB)
A novel ITS-specific primer pair was constructed based on the internal transcribed spacer region of P. croceum and primers were constructed to target the intergenic region between two open reading frames (ORFs) based on the available genomic data for this species
The limits of detection for real-time PCR with the AcH107, ITSP1- and Pilo127 primers were determined by creating dilution series of bacterial and fungal DNA

Summary

Introduction

Mycorrhizal mycelium and microbes are important and potentially interacting factors shaping the performance of mycorrhization helper bacteria (MHB). While the effects of MHB on mycorrhizal fungi have been investigated extensively in vitro, the effects of the fungi on the MHB have largely been neglected In their seminal work, Frey-Klett et al [9] reported that the life span of the Pseudomonas fluorescens strain BBc6R8 was significantly prolonged by exposure to the EM-fungus L. bicolor S238N. Frey-Klett et al [9] reported that the life span of the Pseudomonas fluorescens strain BBc6R8 was significantly prolonged by exposure to the EM-fungus L. bicolor S238N This effect was attributed to the fungus because the survival of the bacterial strain was not affected by the presence of non-mycorrhizal roots

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Discussion

Conclusion