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

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.

Synergists and antagonists in the rhizosphere modulate microbial communities and growth of Quercus robur L.

“…Previous studies have demonstrated that Streptomyces sp. AcH 505 can promote the mycorrhizal colonization rate at different stages of bacteriumefunguseplant interactions, including spore germination, thereby acting as a mycorrhizal helper bacteria (Riedlinger et al, 2006;Tarkka and Frey-Klett, 2008;Kurth et al, 2013). In the present study Streptomyces fostered the growth of P. croceum in oaks at stage B, according to the higher amounts of specific FA biomarkers for the respective symbiont (18:1 u9 and 18:2 u6,9) at second harvest.…”

“…The amount of AcH 505 was estimated from soil samples by quantitative real-time PCR (Smith and Osborn, 2009) according to Kurth et al (2013) with primers targeting the intergenic region between the gyrA and gyrB genes of the AcH 505 genome. Briefly, total DNA was extracted from soil samples and DNA quantity and quality were estimated using a spectrophotometer and agarose gel electrophoresis.…”

Mycorrhization between Cistus ladanifer L. and Boletus edulis Bull is enhanced by the mycorrhiza helper bacteria Pseudomonas fluorescens Migula

“…Given that B. edulis is a comparatively slow growing ECM fungus in saprophytic conditions (Olaizola 2007), P. fluorescens and B. edulis may be competing for nutrients during the presymbiotic period, and consequently, B. edulis may have not been benefited by the bacteria before mycorrhization. Kurth et al (2013) also suggested that the competition between fungus and bacteria for resources may inhibit mycorrhizal development, and Duponnois (1992) reported that high bacterial inoculum doses may also inhibit mycorrhizal development. Thus, the development of methods to quantify the abundance of bacteria and fungus in the presence of one another needs further investigation.…”

“…In either case, they are referred to as MHB (Garbaye 1994). The mechanisms by which bacteria interact with fungi involve the stimulation of mycelial growth, the increase of contact points between roots and fungi, and the reduction of environmental stress on the mycelium (Brulé et al 2001;Kurth et al 2013). Nonetheless, the activity of bacteria can also be detrimental to the mycorrhizal symbiosis in some cases (Kataoka et al 2009).…”

The alleviation of reforestation challenges by beneficial soil microorganisms

“…There is also an option of using a co-inoculation approach; literature confirms that mycorrhizal fungi used with PGPR may act synergistically (Gamalero et al 2010). An important amount of soil microorganisms are known as mycorrhization helper bacteria (MHB), which are capable to stimulate hyphal growth and assist mycorrhization (Kurth et al 2013). Some of the main MHBs are members of Agrobacterium, Azospirillum, Azotobacter, Burkholderia, Bradyrhizobium, Enterobacter, Pseudomonas, Klebsiella, Rhizobium, Bacillus, Brevibacillus, Paenibacillus, Rhodococcus, Streptomyces, Arthrobacter genera (Frey-Klett et al 2007).…”