Transcriptional Landscape of Ectomycorrhizal Fungi and Their Host Provides Insight into N Uptake from Forest Soil

Although EMF are well known for their role in supporting tree N nutrition, the molecular mechanisms underlying N flux from the soil solution into the host through the ectomycorrhizal pathway remain widely unknown. Furthermore, ammonium and nitrate availability in the soil solution is subject to frequent oscillations that create a dynamic environment for the tree roots and associated microbes during N acquisition.

Epigenetic Regulation of Nostoc punctiforme ATCC 29133 in Response to Nitrogen Availability

Here, we report the restriction modification system of Nostoc punctiforme ATCC 29133, along with its methylated genome sequence, under contrasting nitrate availability. Generated methylation profiles revealed increased methylation for key enzymes of assimilatory nitrate reduction, suggesting that Nostoc punctiforme employs DNA methylation to regulate its nitrogen metabolism.

Relative abundance of nitrogen cycling microbes in coral holobionts reflects environmental nitrate availability

Recent research suggests that nitrogen (N) cycling microbes are important for coral holobiont functioning. In particular, coral holobionts may acquire bioavailable N via prokaryotic dinitrogen (N 2 ) fixation or remove excess N via denitrification activity. However, our understanding of environmental drivers on these processes in hospite remains limited. Employing the strong seasonality of the central Red Sea, this study assessed the effects of environmental parameters on the proportional abundances of N cycling microbes associated with the hard corals Acropora hemprichii and Stylophora pistillata. Specifically, we quantified changes in the relative ratio between nirS and nifH gene copy numbers, as a proxy for seasonal shifts in denitrification and N 2 fixation potential in corals, respectively. In addition, we assessed coral tissue-associated Symbiodiniaceae cell densities and monitored environmental parameters to provide a holobiont and environmental context, respectively. While ratios of nirS to nifH gene copy numbers varied between seasons, they revealed similar seasonal patterns in both coral species, with ratios closely following patterns in environmental nitrate availability. Symbiodiniaceae cell densities aligned with environmental nitrate availability, suggesting that the seasonal shifts in nirS to nifH gene abundance ratios were probably driven by nitrate availability in the coral holobiont. Thereby, our results suggest that N cycling in coral holobionts probably adjusts to environmental conditions by increasing and/or decreasing denitrification and N 2 fixation potential according to environmental nitrate availability. Microbial N cycling may, thus, extenuate the effects of changes in environmental nitrate availability on coral holobionts to support the maintenance of the coral–Symbiodiniaceae symbiosis.

Ciprofloxacin Effects On Nitrogren Cycling Processes In Freshwater Aquatic Sediments

Four experiments were designed to assess the effect of ciprofloxacin (cipro) on the function of microbial populations in freshwater environments, specifically on nitrogen cycling. Cipro is a broad-spectrum fluoroquinolone antibiotic used in the treatment of both human and veterinary pathogenic diseases. Previous studies reported the presence of cipro in aquatic environments. This study investigates whether cipro has adverse effects on environmental bacteria which perform critical ecosystem processes associated with the nitrogen cycle. Microcosms containing sediment and synthetic lake water were amended with a series of environmentally relevant concentrations of cipro ranging from 0.5 to 2.5 mg cipro per kg of sediment. Nitrogen cycling processes including nitrification, denitrification and ammonification were measured using a combination of flux measurements (NH4+, NO3-, NO2-), stable isotope techniques ( 15[superscript]N NO₃- dilution) and changes in N₂:Ar and O₂:Ar using Membrane Isotope Mass Spectroscopy (MIMS). Results indicate that cipro has a dose-dependent effect on nitrification, while denitrification is dependent on nitrate availability and may be stimulated by cipro. Ammonification and respiration were not affected at these concentrations. Impacts on nitrification and denitrification are likely to be realized only at the highest concentrations measured in the environment. At the lower end of the environmentally relevant concentration range, observed impacts are not likely to be ecologically important, especially when averaged over an entire lake ecosystem.

Ciprofloxacin Effects On Nitrogren Cycling Processes In Freshwater Aquatic Sediments

Four experiments were designed to assess the effect of ciprofloxacin (cipro) on the function of microbial populations in freshwater environments, specifically on nitrogen cycling. Cipro is a broad-spectrum fluoroquinolone antibiotic used in the treatment of both human and veterinary pathogenic diseases. Previous studies reported the presence of cipro in aquatic environments. This study investigates whether cipro has adverse effects on environmental bacteria which perform critical ecosystem processes associated with the nitrogen cycle. Microcosms containing sediment and synthetic lake water were amended with a series of environmentally relevant concentrations of cipro ranging from 0.5 to 2.5 mg cipro per kg of sediment. Nitrogen cycling processes including nitrification, denitrification and ammonification were measured using a combination of flux measurements (NH4+, NO3-, NO2-), stable isotope techniques ( 15[superscript]N NO₃- dilution) and changes in N₂:Ar and O₂:Ar using Membrane Isotope Mass Spectroscopy (MIMS). Results indicate that cipro has a dose-dependent effect on nitrification, while denitrification is dependent on nitrate availability and may be stimulated by cipro. Ammonification and respiration were not affected at these concentrations. Impacts on nitrification and denitrification are likely to be realized only at the highest concentrations measured in the environment. At the lower end of the environmentally relevant concentration range, observed impacts are not likely to be ecologically important, especially when averaged over an entire lake ecosystem.

Biochemical and Proteomic Changes in the Roots of M4 Grapevine Rootstock in Response to Nitrate Availability

In agricultural soils, nitrate (NO3−) is the major nitrogen (N) nutrient for plants, but few studies have analyzed molecular and biochemical responses involved in its acquisition by grapevine roots. In viticulture, considering grafting, NO3− acquisition is strictly dependent on rootstock. To improve the knowledge about N nutrition in grapevine, this study analyzed biochemical and proteomic changes induced by, NO3− availability, in a hydroponic system, in the roots of M4, a recently selected grapevine rootstock. The evaluation of biochemical parameters, such as NO3−, sugar and amino acid contents in roots, and the abundance of nitrate reductase, allowed us to define the time course of the metabolic adaptations to NO3− supply. On the basis of these results, the proteomic analysis was conducted by comparing the root profiles in N-starved plants and after 30 h of NO3− resupply. The analysis quantified 461 proteins, 26% of which differed in abundance between conditions. Overall, this approach highlighted, together with an increased N assimilatory metabolism, a concomitant rise in the oxidative pentose phosphate pathway and glycolysis, needed to fulfill the redox power and carbon skeleton demands, respectively. Moreover, a wide modulation of protein and amino acid metabolisms and changes of proteins involved in root development were observed. Finally, some results open new questions about the importance of redox-related post-translational modifications and of NO3− availability in modulating the dialog between root and rhizosphere.