Antifungal rhizosphere bacteria can increase as response to the presence of saprotrophic fungi

Acknowledgments: Funding was provided by the Netherlands Organisation for Scientific Research (NWO) in the form of a personal Veni grant to A.v.d.W. This is publication number 5923 of the NIOO-KNAW Netherlands Institute of Ecology. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD

Use of model systems to understand the etiology of fragile X-associated primary ovarian insufficiency (FXPOI)

Fragile X-associated primary ovarian insufficiency (FXPOI) is among the family of disorders caused by the expansion of a CGG repeat sequence in the 5' untranslated region of the X-linked gene FMR1. About 20% of women who carry the premutation allele (55 to 200 unmethylated CGG repeats) develop hypergonadotropic hypogonadism and cease menstruating before age 40. Some proportion of those who are still cycling show hormonal profiles indicative of ovarian dysfunction. FXPOI leads to subfertility and an increased risk of medical conditions associated with early estrogen deficiency. Little progress has been made in understanding the etiology of this clinically significant disorder. Understanding the molecular mechanisms of FXPOI requires a detailed knowledge of ovarian FMR1 mRNA and FMRP’s function. In humans, non-invasive methods to discriminate the mechanisms of the premutation on ovarian function are not available, thus necessitating the development of model systems. Vertebrate (mouse and rat) and invertebrate (Drosophila melanogaster) animal studies for the FMR1 premutation and ovarian function exist and have been instrumental in advancing our understanding of the disease phenotype. For example, rodent models have shown that FMRP is highly expressed in oocytes where it is important for folliculogenesis. The two premutation mouse models studied to date show evidence of ovarian dysfunction and, together, suggest that the long repeat in the transcript itself may have some pathological effect quite apart from any effect of the toxic protein. Further, ovarian morphology in young animals appears normal and the primordial follicle pool size does not differ from that of wild-type animals. However, there is a progressive premature decline in the levels of most follicle classes. Observations also include granulosa cell abnormalities and altered gene expression patterns. Further comparisons of these models are now needed to gain insight into the etiology of the ovarian dysfunction. Premutation model systems in non-human primates and those based on induced pluripotent stem cells show particular promise and will complement current models. Here, we review the characterization of the current models and describe the development and potential of the new models. Finally, we will discuss some of the molecular mechanisms that might be responsible for FXPOI

Bacterial numbers and fungal biomass (ergosterol) after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms.

<p>1A: Number of bacterial colony forming units in the <i>Carex</i> rhizosphere (root-adhering sand); * indicates significant difference (p < 0.05) between microcosms with and without (control) the presence of inoculated fungi, # indicates p = 0.052 for Log-transformed data. 1B: Ergosterol concentrations. r indicates rhizophere sand (sand adhering to <i>Carex</i> roots), nr indicates sand remaining after removal of <i>Carex</i> roots. * indicates significant difference (p < 0.05) within fungal treatments between root-adhering and non-root-adhering sand. Data for both figures are the averages of 5 or 6 sand microcosms. Error bars represent standard deviation.</p

Schematic illustration of possible stimulation of biocontrol of soil-borne pathogenic fungi by increase of saprotrophic fungi.

<p>Organic amendments and/or other measures that stimulate growth of saprotrophic fungi can result in an increase of uptake of rhizodeposits by these fungi and, consequently, in an increase of competitive fungal pressure towards rhizosphere bacteria. As a result bacteria that are antagonistic against fungi will increase and several of these bacteria may also be antagonistic against soil-borne pathogenic fungi and form a natural barrier against fungal diseases. An advantage over introduction of antifungal biocontrol strains is that the fungus-induced stimulation occurs <i>in situ</i> with indigenous soil bacteria that are adapted to the local environmental conditions.</p

Pictures of the experimental set-up of sand microcosms with <i>Carex arenaria</i> (sand sedge) plants.

<p>Pictures of the experimental set-up of sand microcosms with <i>Carex arenaria</i> (sand sedge) plants.</p

Percentage of rhizosphere bacterial isolates positive for different enzyme activities.

<p>Bacterial isolates were obtained from root-adhering soil after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms. * indicates significant difference (p < 0.05) between microcosms with and without pre-inoculation of fungi. Note that experiment 1 and 2 started with different bacterial inoculums as indicated in Material & Methods. Data are the averages of three randomly selected sand microcosms. Error bars represent standard deviation. For each microcosm 40 bacterial isolates were individually screened for the different enzyme activities.</p

Percentage of rhizosphere bacteria isolates with <i>in vitro</i> antagonistic activity against different fungi.

<p>Bacterial isolates were obtained from root-adhering soil after 6 weeks of growth of <i>Carex arenaria</i> seedlings in quartz sand microcosms. * indicates significant difference (p < 0.05) between microcosms with and without pre-inoculation of fungi, for the ANOVA test of data of the white column in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0137988#pone.0137988.g003" target="_blank">Fig 3B</a> Log transformation was applied; # indicates p = 0.072. Note that experiment 1 and 2 started with different bacterial inoculums a as indicated in Material & Methods. Data are the averages of three randomly selected sand microcosms. Error bars represent standard deviation. For each microcosm 40 bacterial isolates were individually screened for in vitro antagonisms against the different fungi.</p

Appendix A. Additional methods (inverted assay and the volatiles analysis), results (pictures, rank abundance, heatmap, NMDS plots), and discussion (dilution approach).

Additional methods (inverted assay and the volatiles analysis), results (pictures, rank abundance, heatmap, NMDS plots), and discussion (dilution approach)