scholarly journals Ectomycorrhizal Fungal Protein Degradation Ability Predicted by Soil Organic Nitrogen Availability

2015 ◽  
Vol 82 (5) ◽  
pp. 1391-1400 ◽  
Author(s):  
Francois Rineau ◽  
Jelle Stas ◽  
Nhu H. Nguyen ◽  
Thomas W. Kuyper ◽  
Robert Carleer ◽  
...  
Keyword(s):  
Organic Matter ◽  
Protein Degradation ◽  
Protease Activity ◽  
Nitrogen Availability ◽  
N Uptake ◽  
Organic N ◽  
Content Type ◽  
N Source ◽  
Ecm Fungi

ABSTRACTIn temperate and boreal forest ecosystems, nitrogen (N) limitation of tree metabolism is alleviated by ectomycorrhizal (ECM) fungi. As forest soils age, the primary source of N in soil switches from inorganic (NH4+and NO3−) to organic (mostly proteins). It has been hypothesized that ECM fungi adapt to the most common N source in their environment, which implies that fungi growing in older forests would have greater protein degradation abilities. Moreover, recent results for a model ECM fungal species suggest that organic N uptake requires a glucose supply. To test the generality of these hypotheses, we screened 55 strains of 13Suillusspecies with different ecological preferences for theirin vitroprotein degradation abilities.Suillusspecies preferentially occurring in mature forests, where soil contains more organic matter, had significantly higher protease activity than those from young forests with low-organic-matter soils or species indifferent to forest age. Within species, the protease activities of ecotypes from soils with high or low soil organic N content did not differ significantly, suggesting resource partitioning between mineral and organic soil layers. The secreted protease mixtures were strongly dominated by aspartic peptidases. Glucose addition had variable effects on secreted protease activity; in some species, it triggered activity, but in others, activity was repressed at high concentrations. Collectively, our results indicate that protease activity, a key ectomycorrhizal functional trait, is positively related to environmental N source availability but is also influenced by additional factors, such as carbon availability.

scholarly journals Do plants use root-derived proteases to promote the uptake of soil organic nitrogen?

2020 ◽  
Vol 456 (1-2) ◽  
pp. 355-367
Author(s):  
Lucy M. Greenfield ◽  
Paul W. Hill ◽  
Eric Paterson ◽  
Elizabeth M. Baggs ◽  
Davey L. Jones
Keyword(s):  
Protease Activity ◽  
Organic Nitrogen ◽  
N Uptake ◽  
Root Surface ◽  
Organic N ◽  
Soil Organic Nitrogen ◽  
Poor Access ◽  
N Deficiency ◽  
Almost All ◽  
Soil Protein

Abstract Aims The capacity of plant roots to directly acquire organic nitrogen (N) in the form of oligopeptides and amino acids from soil is well established. However, plants have poor access to protein, the central reservoir of soil organic N. Our question is: do plants actively secrete proteases to enhance the breakdown of soil protein or are they functionally reliant on soil microorganisms to undertake this role? Methods Growing maize and wheat under sterile hydroponic conditions with and without inorganic N, we measured protease activity on the root surface (root-bound proteases) or exogenously in the solution (free proteases). We compared root protease activities to the rhizosphere microbial community to estimate the ecological significance of root-derived proteases. Results We found little evidence for the secretion of free proteases, with almost all protease activity associated with the root surface. Root protease activity was not stimulated under N deficiency. Our findings suggest that cereal roots contribute one-fifth of rhizosphere protease activity. Conclusions Our results indicate that plant N uptake is only functionally significant when soil protein is in direct contact with root surfaces. The lack of protease upregulation under N deficiency suggests that root protease activity is unrelated to enhanced soil N capture.

scholarly journals Interactions between uptake of amino acids and inorganic nitrogen in wheat plants

2011 ◽  
Vol 8 (6) ◽  
pp. 11311-11335 ◽  
Author(s):  
E. Gioseffi ◽  
A. de Neergaard ◽  
J. K. Schjoerring
Keyword(s):  
Amino Acids ◽  
Nutrient Solution ◽  
Inorganic Nitrogen ◽  
N Uptake ◽  
Organic N ◽  
Arable Soils ◽  
Inorganic N ◽  
N Losses ◽  
Total N ◽  
N Source

Abstract. Soil-borne amino acids may constitute a nitrogen (N) source for plants in various terrestrial ecosystems but their importance for total N nutrition is unclear, particularly in nutrient-rich arable soils. One reason for this uncertainty is lack of information on how the absorption of amino acids by plant roots is affected by the simultaneous presence of inorganic N forms. The objective of the present study was to study absorption of glycine (Gly) and glutamine (Gln) by wheat roots and their interactions with nitrate (NO3–) and (NH4+) during uptake. The underlying hypothesis was that amino acids, when present in nutrient solution together with inorganic N, may lead to down-regulation of the inorganic N uptake. Amino acids were enriched with double-labelled 15N and 13C, while NO3– and NH4+ acquisition was determined by their rate of removal from the nutrient solution surrounding the roots. The uptake rates of NO3– and NH4+ did not differ from each other and were about twice as high as the uptake rate of organic N when the different N forms were supplied separately in concentrations of 2 mM. Nevertheless, replacement of 50 % of the inorganic N with organic N was able to restore the N uptake to the same level as that in the presence of only inorganic N. Co-provision of NO3– did not affect glycine uptake, while the presence of glycine down-regulated NO3– uptake. The ratio between 13C and 15N were lower in shoots than in roots and also lower than the theoretical values, reflecting higher C losses via respiratory processes compared to N losses. It is concluded that organic N can constitute a significant N-source for wheat plants and that there is an interaction between the uptake of inorganic and organic nitrogen.

scholarly journals Rhb1 Regulates the Expression of Secreted Aspartic Protease 2 through the TOR Signaling Pathway in Candida albicans

2011 ◽  
Vol 11 (2) ◽  
pp. 168-182 ◽  
Author(s):  
Yu-Ting Chen ◽  
Chia-Ying Lin ◽  
Pei-Wen Tsai ◽  
Cheng-Yao Yang ◽  
Wen-Ping Hsieh ◽  
...  
Keyword(s):  
Candida Albicans ◽  
Signaling Pathway ◽  
Virulence Factor ◽  
Nitrogen Availability ◽  
Target Genes ◽  
Small Gtpase ◽  
Aspartic Protease ◽  
Tor Signaling ◽  
Content Type

ABSTRACTCandida albicansis a major fungal pathogen in humans. InC. albicans, secreted aspartyl protease 2 (Sap2) is the most highly expressed secreted aspartic proteasein vitroand is a virulence factor. Recent research links the small GTPase Rhb1 toC. albicanstarget of rapamycin (TOR) signaling in response to nitrogen availability. The results of this study show that Rhb1 is related to cell growth through the control ofSAP2expression when protein is the major nitrogen source. This process involves various components of the TOR signaling pathway, including Tor1 kinase and its downstream effectors. TOR signaling not only controlsSAP2transcription but also affects Sap2 protein levels, possibly through general amino acid control. DNA microarray analysis identifies other target genes downstream of Rhb1 in addition toSAP2. These findings provide new insight into nutrients, Rhb1-TOR signaling, and expression ofC. albicansvirulence factor.

Effects of modifying plant carbon inputs on nitrogen distribution in intact cores of a perennial grass pasture

Soil Research ◽  
1995 ◽  
Vol 33 (2) ◽  
pp. 297 ◽  
Author(s):  
FA Robertson ◽  
RJK Myers ◽  
PG Saffigna
Keyword(s):  
Organic Matter ◽  
Soil Organic Matter ◽  
Microbial Biomass ◽  
N Uptake ◽  
Organic N ◽  
Root Pruning ◽  
Panicum Maximum ◽  
15N Recovery ◽  
N Availability ◽  
Plant Shoots

Perennial pastures can accumulate large quantities of roots and surface litter of high C:N ratio, which may reduce N availability to the plant by stimulating microbial immobilization. We studied the effects of modifying carbon inputs from roots and litter on the distribution of nitrogen (N) in plant and soil fractions of an old N-deficient green panic (Panicum maximum var. trichoglume) pasture. Intact pasture cores were taken from the field to a glasshouse, and the surface litter was removed before applying the following treatments: (i) surface litter added, (ii) roots pruned to kill approximately 60% of roots, and (iii) plant shoots removed. A small pulse of 15N as ammonium sulfate was added to the soil surface, and the cores were destructively sampled on several occasions over the following 4 months. Litter addition had little effect on N uptake by uncut plants. When plant shoots were removed, litter markedly reduced plant N uptake. Litter increased N and 15N in microbial biomass and N and 15N stabilized in non-biomass soil organic matter, and reduced loss of N from the cores. Root pruning had little effect on N distribution, except for an initial reduction in plant uptake. Removal of pasture shoots markedly increased soil nitrate and loss of 15N, and decreased non-biomass organic N and 15N. Recovery of 15N in non-biomass organic matter was around three times greater than 15N in microbial biomass, and was closely associated with microbial CO2 production. There was evidence that 15N entered the non-biomass organic matter by both abiotic and microbially mediated processes. In these pastures, the non-biomass soil organic matter may be a more important sink for N than the microbial biomass.

scholarly journals Identification of SlpB, a Cytotoxic Protease from Serratia marcescens

2015 ◽  
Vol 83 (7) ◽  
pp. 2907-2916 ◽  
Author(s):  
Robert M. Q. Shanks ◽  
Nicholas A. Stella ◽  
Kristin M. Hunt ◽  
Kimberly M. Brothers ◽  
Liang Zhang ◽  
...  
Keyword(s):  
Serratia Marcescens ◽  
Cell Line ◽  
Cell Lines ◽  
Protease Activity ◽  
Opportunistic Pathogen ◽  
Bioinformatic Analysis ◽  
Protease Production ◽  
Type I ◽  
Content Type

The Gram-negative bacterium and opportunistic pathogenSerratia marcescenscauses ocular infections in healthy individuals. Secreted protease activity was characterized from 44 ocular clinical isolates, and a higher frequency of protease-positive strains was observed among keratitis isolates than among conjunctivitis isolates. A positive correlation between protease activity and cytotoxicity to human corneal epithelial cellsin vitrowas determined. Deletion ofprtSin clinical keratitis isolate K904 reduced, but did not eliminate, cytotoxicity and secreted protease production. This indicated that PrtS is necessary for full cytotoxicity to ocular cells and implied the existence of another secreted protease(s) and cytotoxic factors. Bioinformatic analysis of theS. marcescensDb11 genome revealed three additional open reading frames predicted to code for serralysin-like proteases noted here asslpB,slpC, andslpD. Induced expression ofprtSandslpB, but notslpCandslpD, in strain PIC3611 rendered the strain cytotoxic to a lung carcinoma cell line; however, onlyprtSinduction was sufficient for cytotoxicity to a corneal cell line. Strain K904 with deletion of bothprtSandslpBgenes was defective in secreted protease activity and cytotoxicity to human cell lines. PAGE analysis suggests that SlpB is produced at lower levels than PrtS. Purified SlpB demonstrated calcium-dependent and AprI-inhibited protease activity and cytotoxicity to airway and ocular cell linesin vitro. Lastly, genetic analysis indicated that the type I secretion system gene,lipD, is required for SlpB secretion. These genetic data introduce SlpB as a new cytotoxic protease fromS. marcescens.

COMPARAISON DE DIFFÉRENTES MÉTHODES D'ANALYSE DE L'AZOTE DU SOL EN RELATION AVEC SA DISPONIBILITÉ POUR LES PLANTES

1987 ◽  
Vol 67 (3) ◽  
pp. 521-531 ◽  
Author(s):  
M. GIROUX ◽  
T. SEN TRAN
Keyword(s):  
Organic Matter ◽  
Soil Nitrogen ◽  
N Uptake ◽  
Relative Yield ◽  
Organic N ◽  
Uv Absorbance ◽  
Soil N ◽  
Plant N Uptake ◽  
Total N ◽  
N Concentration

The objective of this study was to compare several methods of estimating the availability of soil nitrogen to plants. Total soil N, organic matter content, mineralized N during a 2 wk incubation at 35 °C, organic N in 6 N HC1, 0.01 M NaHCO3 and 1 N KCl extracts, and finally mineral N extracted by 2 N KCl were evaluated and contrasted with N uptake by sugar beets cultivated on 19 soils in a greenhouse experiment. The relative yield or plant N uptake gave the highest correlation coefficients when both mineral and organic N fractions in soil extract were considered. The incubation methods gave the best correlation coefficient with relative yield (R2 = 0.85**). N contents in NaHCO3 extract were more correlated with relative yield or N uptake than total N, organic matter contents or N extracted by 6 N HCl or 1 N KCl. The UV absorbance values obtained at 205 nm with 0.01 M NaHCO3 extract were also well correlated with relative yield (R2 = 0.78**) and plant N uptake (R2 = 0.66**). At this wavelength, as well as at 220 nm, the absorbance was affected by mineral and organic N contents in the extract. However, at 260 nm, the UV absorbance was only related to organic N in the extract; consequently these absorbance values were less correlated with relative yield (R2 = 0.49**) or N uptake (R2 = 0.27*). Furthermore, the absorbance measured at 205 nm was too sensitive to NO3-N and organic N concentration and this relationship was not linear in the high-N concentration range. The UV absorbance at 220 nm in the 0.01M NaHCO3 extract seemed to be a promising method to evaluate the availability of soil N. Key words: Soil nitrogen, incubation, ultraviolet absorbance, hydrolyzable nitrogen

scholarly journals Involutin Is an Fe3+Reductant Secreted by the Ectomycorrhizal Fungus Paxillus involutus during Fenton-Based Decomposition of Organic Matter

2015 ◽  
Vol 81 (24) ◽  
pp. 8427-8433 ◽  
Author(s):  
Firoz Shah ◽  
Daniel Schwenk ◽  
César Nicolás ◽  
Per Persson ◽  
Dirk Hoffmeister ◽  
...  
Keyword(s):  
Organic Matter ◽  
Ectomycorrhizal Fungi ◽  
Brown Rot ◽  
Ectomycorrhizal Fungus ◽  
Organic Matter Decomposition ◽  
Mineral Nutrient ◽  
Paxillus Involutus ◽  
Fenton Chemistry ◽  
Content Type

ABSTRACTEctomycorrhizal fungi play a key role in mobilizing nutrients embedded in recalcitrant organic matter complexes, thereby increasing nutrient accessibility to the host plant. Recent studies have shown that during the assimilation of nutrients, the ectomycorrhizal fungusPaxillus involutusdecomposes organic matter using an oxidative mechanism involving Fenton chemistry (Fe2++ H2O2+ H+→ Fe3++ ˙OH + H2O), similar to that of brown rot wood-decaying fungi. In such fungi, secreted metabolites are one of the components that drive one-electron reductions of Fe3+and O2, generating Fenton chemistry reagents. Here we investigated whether such a mechanism is also implemented byP. involutusduring organic matter decomposition. Activity-guided purification was performed to isolate the Fe3+-reducing principle secreted byP. involutusduring growth on a maize compost extract. The Fe3+-reducing activity correlated with the presence of one compound. Mass spectrometry and nuclear magnetic resonance (NMR) identified this compound as the diarylcyclopentenone involutin. A major part of the involutin produced byP. involutusduring organic matter decomposition was secreted into the medium, and the metabolite was not detected when the fungus was grown on a mineral nutrient medium. We also demonstrated that in the presence of H2O2, involutin has the capacity to drive anin vitroFenton reaction via Fe3+reduction. Our results show that the mechanism for the reduction of Fe3+and the generation of hydroxyl radicals via Fenton chemistry by ectomycorrhizal fungi during organic matter decomposition is similar to that employed by the evolutionarily related brown rot saprotrophs during wood decay.

scholarly journals Urea Uptake and Carbon Fixation by Marine Pelagic Bacteria and Archaea during the Arctic Summer and Winter Seasons

2014 ◽  
Vol 80 (19) ◽  
pp. 6013-6022 ◽  
Author(s):  
Tara L. Connelly ◽  
Steven E. Baer ◽  
Joshua T. Cooper ◽  
Deborah A. Bronk ◽  
Boris Wawrik
Keyword(s):  
Carbon Fixation ◽  
N Uptake ◽  
Ammonium Uptake ◽  
The Arctic ◽  
Organic N ◽  
Content Type ◽  
Group I ◽  
N Utilization ◽  
Uptake Rates ◽  
Arctic Summer

ABSTRACTHow Arctic climate change might translate into alterations of biogeochemical cycles of carbon (C) and nitrogen (N) with respect to inorganic and organic N utilization is not well understood. This study combined15N uptake rate measurements for ammonium, nitrate, and urea with15N- and13C-based DNA stable-isotope probing (SIP). The objective was to identify active bacterial and archeal plankton and their role in N and C uptake during the Arctic summer and winter seasons. We hypothesized that bacteria and archaea would successfully compete for nitrate and urea during the Arctic winter but not during the summer, when phytoplankton dominate the uptake of these nitrogen sources. Samples were collected at a coastal station near Barrow, AK, during August and January. During both seasons, ammonium uptake rates were greater than those for nitrate or urea, and nitrate uptake rates remained lower than those for ammonium or urea. SIP experiments indicated a strong seasonal shift of bacterial and archaeal N utilization from ammonium during the summer to urea during the winter but did not support a similar seasonal pattern of nitrate utilization. Analysis of 16S rRNA gene sequences obtained from each SIP fraction implicated marine group ICrenarchaeota(MGIC) as well asBetaproteobacteria,Firmicutes, SAR11, and SAR324 in N uptake from urea during the winter. Similarly,13C SIP data suggested dark carbon fixation for MGIC, as well as for several proteobacterial lineages and theFirmicutes. These data are consistent with urea-fueled nitrification by polar archaea and bacteria, which may be advantageous under dark conditions.

scholarly journals ClpAP proteolysis does not require rotation of the ClpA unfoldase relative to ClpP

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Sora Kim ◽  
Kristin L Zuromski ◽  
Tristan A Bell ◽  
Robert T Sauer ◽  
Tania A Baker
Keyword(s):  
Protein Degradation ◽  
Protease Activity ◽  
Protein Substrates ◽  
Hand Model ◽  
Clpap Protease ◽  
Optimal Function

AAA+ proteases perform regulated protein degradation in all kingdoms of life and consist of a hexameric AAA+ unfoldase/translocase in complex with a self-compartmentalized peptidase. Based on asymmetric features of cryo-EM structures and a sequential hand-over-hand model of substrate translocation, recent publications have proposed that the AAA+ unfoldases ClpA and ClpX rotate with respect to their partner peptidase ClpP to allow function. Here, we test this model by covalently crosslinking ClpA to ClpP to prevent rotation. We find that crosslinked ClpAP complexes unfold, translocate, and degrade protein substrates in vitro, albeit modestly slower than uncrosslinked enzyme controls. Rotation of ClpA with respect to ClpP is therefore not required for ClpAP protease activity, although some flexibility in how the AAA+ ring docks with ClpP may be necessary for optimal function.

scholarly journals SppI Forms a Membrane Protein Complex with SppA and Inhibits Its Protease Activity in Bacillus subtilis

mSphere ◽  
2020 ◽  
Vol 5 (5) ◽  
Author(s):  
Gabriela Henriques ◽  
Stephen McGovern ◽  
Jolanda Neef ◽  
Minia Antelo-Varela ◽  
Friedrich Götz ◽  
...  
Keyword(s):  
Bacillus Subtilis ◽  
Membrane Protein ◽  
Antimicrobial Peptides ◽  
Protease Activity ◽  
Cationic Antimicrobial Peptide ◽  
Content Type ◽  
Terminal Domain ◽  
Increased Sensitivity

ABSTRACT The membrane protease SppA of Bacillus subtilis was first described as a signal peptide peptidase and later shown to confer resistance to lantibiotics. Here, we report that SppA forms octameric complexes with YteJ, a membrane protein of thus-far-unknown function. Interestingly, sppA and yteJ deletion mutants exhibited no protein secretion defects. However, these mutant strains differed significantly in their resistance to antimicrobial peptides. In particular, sppA mutant cells displayed increased sensitivity to the lantibiotics nisin and subtilin and the human lysozyme-derived cationic antimicrobial peptide LP9. Importantly, YteJ was shown to antagonize SppA activity both in vivo and in vitro, and this SppA-inhibitory activity involved the C-terminal domain of YteJ, which was therefore renamed SppI. Most likely, SppI-mediated control is needed to protect B. subtilis against the potentially detrimental protease activity of SppA since a mutant overexpressing sppA by itself displayed defects in cell division. Altogether, we conclude that the SppA-SppI complex of B. subtilis has a major role in protection against antimicrobial peptides. IMPORTANCE Our study presents new insights into the molecular mechanism that regulates the activity of SppA, a widely conserved bacterial membrane protease. We show that the membrane proteins SppA and SppI form a complex in the Gram-positive model bacterium B. subtilis and that SppI inhibits SppA protease activity in vitro and in vivo. Furthermore, we demonstrate that the C-terminal domain of SppI is involved in SppA inhibition. Since SppA, through its protease activity, contributes directly to resistance to lantibiotic peptides and cationic antibacterial peptides, we propose that the conserved SppA-SppI complex could play a major role in the evasion of bactericidal peptides, including those produced as part of human innate immune defenses.

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