Screening of epoxide hydrolase producing microorganisms for biotransformation of deoxynivalenol

Deoxynivalenol (DON) transformation products from selected time course experiments were analyzed by thin-layer chromatography. With the strainAlternaria alternata f. sp.lycopersici AS27-3, one major metabolite of DON in ethyl acetate was observed. This unidentified metabolite was more polar than DON and has a R_f value of 0.71. Derivatization indicated that this metabolite was probably an unidentified trichothecene. Screening of 29 other microbial isolates (bacteria, yeast, filamentous fungi) for DON transformation did not result in any active organism. Presented at the 26^th Mykotoxin-Workshop in Herrching, Germany, May 17–19, 2004     

Nutrient and mineralogical control on dissolved organic C, N and P fluxes and stoichiometry in Hawaiian soils

We measured DOM fluxes from the O horizon of Hawaiiansoils that varied in nutrient availability and mineralcontent to examine what regulates the flux ofdissolved organic carbon (DOC), nitrogen (DON) andphosphorus (DOP) from the surface layer of tropicalsoils. We examined DOM fluxes in a laboratory study from N, P and N+Pfertilized and unfertilized sites on soils that rangedin age from 300 to 4 million years old. The fluxesof DOC and DON were generally related to the % Cand % N content of the soils across the sites. Ingeneral, CO₂ and DOC fluxes were not correlatedsuggesting that physical desorption, dissolution andsorption reactions primarily control DOM release fromthese surface horizons. The one exception to thispattern was at the oldest site where there was asignificant relationship between DOC and CO₂flux. The oldest site also contained the lowestmineral and allophane content of the three sites andthe DOC-respiration correlation indicates arelationship between microbial activity and DOC fluxat this site. N Fertilization increased DON fluxes by50% and decreased DOC:DON ratios in the youngest,most N poor site. In the older, more N rich sites, Nfertilization neither increased DON fluxes nordecreased DOM C:N ratios. Similarly, short termchanges in N availability in laboratory-based soil Nand P fertilization experiments did not affect the DOMC:N ratios of leachate. DOM C:N ratios were similar tosoil organic matter C:N ratios, and changes in DOM C:Nratios with fertilization appeared to have beenmediated through long term effects on SOM C:N ratiosrather than through changes in microbial demand for Cand N. There was no relationship between DON andinorganic N flux during these incubations suggestingthat the organic and inorganic components of N fluxfrom soils are regulated by different factors and thatDON fluxes are not coupled to immediate microbialdemand for N. In contrast to the behavior of DON, thenet flux of dissolved organic phosphorus (DOP) and DOMC:P ratios responded to both long-term P fertilizationand natural variation in reactive P availability. There was lower DOP flux and higher DOM C:P ratiosfrom soils characterized by low P availability andhigh DOP flux and narrow DOM C:P ratios in sites withhigh P availability. DOP fluxes were also closelycorrelated with dissolved inorganic P fluxes. PFertilization increased DOP fluxes by 73% in theyoungest site, 31% in the P rich intermediate agesite and 444% in the old, P poor site indicating thatDOP fluxes closely track P availability in soils.     

森林生态系统DOM的来源、特性及流动

可溶性有机物质（Dissolved Organic Matter)是森林生态系统主要的可移动碳库及重要的养分库。系统综述了森林生态系统DOM的来源,组成,性质,季节动态;DOM释放与存留机制及影响因素,森林生态系统DOM的流动及干扰对DOM动态影响等,已有研究表明DOM的森林生态系统C、N、P循环,成土作用,污染物迁移等方面起着重要作用。今后森林生态系统DOM的研究应集中于以几方面：（1）确定森林生态系统中DOM源和汇;（2）评价森林水文条件对DOM释放与存留的调节作用;（3）探讨全球气候变化对森林生态系统DOM的影响;（4）可溶性有机氮（Dissolved Organic Nitrogen),可溶性有机磷（Dissolved Organic Phosphorus)动态与可溶性有碳（Dissolved Organic Carbon）动态的差别。     

A mechanism of abiotic immobilization of nitrate in forest ecosystems: the ferrous wheel hypothesis

Forest soils, rather than woody biomass, are the dominant long‐term sink for N in forest fertilization studies and, by inference, for N from atmospheric deposition. Recent evidence of significant abiotic immobilization of inorganic‐N in forest humus layers challenges a previously widely held view that microbial processes are the dominant pathways for N immobilization in soil. Understanding the plant, microbial, and abiotic mechanisms of N immobilization in forest soils has important implications for understanding current and future carbon budgets. Abiotic immobilization of nitrate is particularly perplexing because the thermodynamics of nitrate reduction in soils are not generally favorable under oxic conditions. Here we present preliminary evidence for a testable hypothesis that explains abiotic immobilization of nitrate in forest soils. Because iron (and perhaps manganese) plays a key role as a catalyst, with Fe(II) reducing nitrate and reduced forms of carbon then regenerating Fe(II), we call this ‘the ferrous wheel hypothesis’. After nitrate is reduced to nitrite, we hypothesize that nitrite reacts with dissolved organic matter through nitration and nitrosation of aromatic ring structures, thus producing dissolved organic nitrogen (DON). In addition to ignorance about mechanisms of DON production, little is known about DON dynamics in soil and its fate within ecosystems. Evidence from leaching and watershed studies suggests that DON production and consumption may be largely uncoupled from seasonal biological processes, although biological processes ultimately produce the DOC and reducing power that affect DON formation and the entire N cycle. The ferrous wheel hypothesis includes both biological and abiological processes, but the reducing power of plant‐derived organic matter may build up over seasons and years while the abiotic reduction of nitrate and reaction of organic matter with nitrite may occur in a matter of seconds after nitrate enters the soil solution.     

Deoxynivalenol (DON) in hartweizen

Deoxynivalenol (DON) in Durum Wheat High contamination levels of deoxynivalenol (DON) were found during an investigation of noodles in 2001 and initiated an additional survey of Durum wheat used as raw material for these products. Analyses of 53 samples of Durum wheat by HPLC revealed 89% positives and a median concentration of 790 ug/kg, which clearly exceeded the EU action level of 500 μg/kg. Based on these findings, producers increased quality controls on Durum wheat. In 2002 a total of 60 samples were analysed and 85% positives found. The median, however, lay at 215 μg/kg, below a probable maximum level of 500 μg/kg and demonstrated the positive efforts of food producers to decrease the contamination levels of DON in pasta products.     

Nitrogen transformations in limed and nitrogen fertilized soil in Norway spruce stands

Nitrogen transformations in the soil, and the resulting changes in carbon and nitrogen compounds in soil percolate water, were studied in two stands of Norway spruce (Picea abies L.). Over the last 30 years the stands were repeatedly limed (total 6000 kg ha^–1), fertilized with nitrogen (total about 900 kg ha^–1), or both treatments together. Both aerobic incubations of soil samples in the laboratory, and intact soil core incubations in the field showed that in control plots ammonification widely predominated over nitrification. In both experiments nitrogen addition increased the formation of mineral-N. In one experiment separate lime and nitrogen treatments increased nitrification, in the other, only lime and nitrogen addition together had this effect. In one experiment immobilization of nitrogen to soil microbial biomass was lower in soil only treated with nitrogen. Soil percolate water was collected by means of lysimeters placed under the humus layer and 10 cm below in the mineral soil. Total N, NH₄-N and NO₃-N were measured, and dissolved organic nitrogen was fractioned according to molecular weight. NO₃-N concentrations in percolate water, collected under the humus layer, were higher in plots treated with N-fertilizer, especially when lime was also added. The treatments had no effect on the N concentrations in mineral soil. A considerable proportion of nitrogen was leached in organic form.     

Uptake of Allochthonous Dissolved Organic Matter from Soil and Salmon in Coastal Temperate Rainforest Streams

Dissolved organic matter (DOM) is an important component of aquatic food webs. We compare the uptake kinetics for NH₄–N and different fractions of DOM during soil and salmon leachate additions by evaluating the uptake of organic forms of carbon (DOC) and nitrogen (DON), and proteinaceous DOM, as measured by parallel factor (PARAFAC) modeling of DOM fluorescence. Seasonal DOM slug additions were conducted in three headwater streams draining a bog, forested wetland, and upland forest using DOM collected by leaching watershed soils. We also used DOM collected from bog soil and salmon carcasses to perform additions in the upland forest stream. DOC uptake velocity ranged from 0.010 to 0.063 mm s⁻¹ and DON uptake velocity ranged from 0.015 to 0.086 mm s⁻¹, which provides evidence for the whole-stream uptake of allochthonous DOM. These findings imply that wetlands could potentially be an important source of DOM to support stream heterotrophic production. There was no significant difference in the uptake of DOC and DON across the soil leachate additions (P > 0.05), although differential uptake of DOM fractions was observed as protein-like fluorescence was removed from the water column more efficiently than bulk DOC and DON (P < 0.05). Moreover, PARAFAC analysis of DOM fluorescence showed that protein-like fluorescence decreased downstream during all DOM additions, whereas humic-like fluorescence did not change. This differential processing in added DOM suggests slow and fast turnover pools exist for aquatic DOM. Taken together, our findings argue that DON could potentially fill a larger role in satisfying biotic N demand in oligotrophic headwater streams than previously thought. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Author contributions  J.B.F. conceived of or designed study, performed research, analyzed data, contributed new methods or models, and wrote the paper. E.H. conceived of or designed study and analyzed data. R.T.E. conceived of or designed study and analyzed data. J.B.J. contributed new methods or models and analyzed data.     

Tracking of fast moving neuronal vesicles with ageladine A

O-Linked β-N-acetylglucosaminylation (O-GlcNAcylation) of nucleocytoplasmic proteins is a ubiquitous post-translational modification in multicellular organisms studied so far. Since aberrant O-GlcNAcylation has a link with insulin resistance, it is important to establish the status of O-GlcNAcylation in differentiation of mesenchymal cells such as preadipocytes. In this study, we found a differentiation-dependent drastic increase in the level of O-GlcNAcylation in mouse 3T3-L1 preadipocytes. The occurrence of the increase in O-GlcNAcylation, which correlated with the expression of C/EBPα, was in part due to increased expression of O-GlcNAc transferase. In addition to the well-known O-GlcNAcylated proteins such as nucleoporins and vimentin, pyruvate carboxylase, long chain fatty acid-CoA ligase 1, and Ewing sarcoma protein were identified as the proteins which are heavily O-GlcNAcylated with the adipocyte differentiation. Both adipocyte differentiation and the differentiation-dependent increase in O-GlcNAcylation were blocked by 6-diazo-5-oxo-norleucine. These results suggest that O-GlcNAcylation particilates, at least in part, in adipogenesis.     

Comparison of Canadian Fusarium graminearum isolates for aggressiveness,vegetative compatibility,and production of ergosterol and mycotoxins

Fusarium graminearum is the predominant pathogen causing fusarium head blight of cereals in North America. Fifteen Canadian isolates of Fusarium graminearum were highly diverse in terms of vegetative compatibility grouping (VCG) and varied for production of ergosterol and mycotoxin production in rice culture. Aggressiveness was assessed by scoring the disease severity incited in wheat spikes by each isolate. Two inoculation methods, single-floret injection and spray of entire spikes, were used to screen 4 wheat varieties for reaction to the F. graminearum isolates. All isolates were of broadly similar aggressiveness, with disease severity ranging from 17.2 to 39.1 for single floret injection, and 39.1 to 69.0 for spray inoculation. Disease severity, ergosterol production, and mycotoxin development were not correlated. Using nitrate non-utilizing mutants the 15 isolates were grouped into 14 VCGs. Deoxynivalenol (DON) was produced by all isolates in rice culture, at levels between 0.2 and 249 ppm. 15-acetyldeoxynivalenol was produced by 14 of the 15 isolates at levels between 0.4 and 44.6 ppm. These results reveal a high level of diversity for several characteristics among F. graminearum isolates from Canada. This revised version was published online in June 2006 with corrections to the Cover Date.