Amylopectin induces fumonisin B1 production by Fusarium verticillioides during colonization of maize kernels

Fusarium verticillioides, a fungal pathogen of maize, produces fumonisin mycotoxins that adversely affect human and animal health. Basic questions remain unanswered regarding the interactions between the host plant and the fungus that lead to the accumulation of fumonisins in maize kernels. In this study, we evaluated the role of kernel endosperm composition in regulating fumonisin B1 (FB1) biosynthesis. We found that kernels lacking starch due to physiological immaturity did not accumulate FB1. Quantitative polymerase chain reaction analysis indicated that kernel development also affected the expression of fungal genes involved in FB1 biosynthesis, starch metabolism, and nitrogen regulation. A mutant strain of F. verticillioides with a disrupted a-amylase gene was impaired in its ability to produce FB1 on starchy kernels, and both the wild-type and mutant strains produced significantly less FB1 on a high-amylose kernel mutant of maize. When grown on a defined medium with amylose as the sole carbon source, the wild-type strain produced only trace amounts of FB1, but it produced large amounts of FB1 when grown on amylopectin or dextrin, a product of amylopectin hydrolysis. We conclude that amylopectin induces FB1 production in F. verticillioides. This study provides new insight regarding the interaction between the fungus and maize kernel during pathogenesis and highlights important areas that need further study.     

Nitrogen repression of fumonisin B1 biosynthesis in Gibberella fujikuroi

Fumonisins are a group of structurally related mycotoxins produced by Gibberella fujikuroi. The fungus produced fumonisin B1 (FB1) as early as 18 hour in a defined medium containing 1.25 mM or 2.5 mM ammonium phosphate, whereas fumonisin B1 production was repressed for 75 hour and 125 hour when mycelia were resuspended in media containing ammonium phosphate at 10 mM or 20 mM, respectively. Although total fumonisin B1 production was greater in resuspension cultures grown in higher concentrations of ammonium phosphate, the accumulation was independent of the inoculum size and carbon/nitrogen ratio. The addition of ammonium phosphate to cracked corn cultures also repressed fumonisin B1 production by 97%, and persisted for at least three weeks. Thus, biosynthesis of fumonisin B1 is regulated by a mechanism involving nitrogen metabolite repression, suggesting that control strategies that target the regulatory elements of nitrogen metabolism may be effective at reducing the risk of fumonisin contamination in food.     

Influence of kernel age on fumonisin B1 production in maize by Fusarium moniliforme.

Production of fumonisins by Fusarium moniliforme on naturally infected maize ears is an important food safety concern due to the toxic nature of this class of mycotoxins. Assessing the potential risk of fumonisin production in developing maize ears prior to harvest requires an understanding of the regulation of toxin biosynthesis during kernel maturation. We investigated the developmental-stage-dependent relationship between maize kernels and fumonisin B1 production by using kernels collected at the blister (R2), milk (R3), dough (R4), and dent (R5) stages following inoculation in culture at their respective field moisture contents with F. moniliforme. Highly significant differences (P 相似文献   

一株高效解磷真菌新菌株的筛选鉴定及解磷特性

从辽宁省辽中县多年耕种的日光温室番茄根际土壤中筛选出一株解磷真菌,通过菌落形态特征和ITS rDNA序列对比,鉴定该菌株为草酸青霉菌的一株新菌株,将其命名为PSF1.该菌株能利用葡萄糖、蔗糖、乳糖、半乳糖、可溶性淀粉等多种碳源和硫酸铵、氯化铵、硝酸铵、硝酸钾、尿素等多种氮源进行生长代谢并表现出较强的解磷能力,在C/N 10∶1~60∶1、初始pH 7~8的条件下生长情况较好且解磷能力较高.该菌株有很强的产酸能力,在培养过程中培养液pH由7.00~7.50下降至2.06~4.87;在4种磷源培养液中的最高解磷量分别为磷酸三钙(869.62 mg·L^-1)>磷矿粉(233.56 mg·L^-1)>磷酸铝(44.77 mg·L^-1)>磷酸铁(28.42 mg·L^-1).Pearson相关分析表明,菌株在磷酸三钙、磷矿粉和磷酸铁培养液中的解磷量与pH的变化之间呈极显著负相关关系,在磷酸铝培养液中无显著相关关系.菌株PSF1解磷能力强,生长条件广,推测其在土壤中有较强的解磷能力.     

Effect of calcium, phosphate and nitrogen on cell growth and biosynthesis of cell wall polysaccharides by Silene vulgaris cell culture

Medium nutrients such as calcium, phosphorus, nitrogen and nitrate to ammonium ratio have significant influence on the growth, biosynthetic and biochemical characteristics of polysaccharides produced by Silene vulgaris (M.) G. cell culture. Cell growth and production of polysaccharides was limited by an absence of any of these components in the medium. Optimal growth of the callus and production of arabinogalactan were achieved at 1.5-4.5 microM calcium while the optimal production of pectin named silenan was observed at 3.0-4.5 microM. The phosphate contents in the medium in the range of 0.63-3.75 microM were favorable for callus growth. Production of silenan was maximal at 1.25-3.75 microM phosphate. Optimal growth of the callus was achieved at 30-90 microM nitrogen. Maximal production of silenan was observed at 60 microM nitrogen while the optimal production of arabinogalactan was at 90 microM nitrogen (at ratio of NH(4)(+):NO(3)(-) as 1:2). A presence both of nitrate and ammonium is needed for the silenan biosynthesis (the NH(4)(+):NO(3)(-) ratio as 1:1 and 1:2). Yields and volumetric production of arabinogalactan were maximal at deletion of ammonium from the nutrient medium (ratio 0:1). Absence of calcium or nitrogen in the medium leads to a decrease of the galacturonic acid residues in silenan. The galactose residues contents in arabinogalactan were decreased in the absence of nitrogen and calcium in the medium.     

磷酸氢二铵对糙皮侧耳菌丝生长及基质降解酶活性的影响

氮源种类和浓度均会对糙皮侧耳Pleurotus ostreatus菌丝长势、生长速率以及代谢产生影响,而氮匮乏与氮过量积累都会对糙皮侧耳的生长产生不利影响。为了研究氮源对糙皮侧耳菌丝生长和基质降解酶活性的影响,本研究选取磷酸氢二铵[(NH4)2HPO4]作为唯一氮源,通过在培养基中添加不同浓度的磷酸氢二铵检测糙皮侧耳菌丝生长速率和木质纤维素降解酶的活性,筛选出糙皮侧耳生长的最适磷酸氢二铵浓度。结果表明,当磷酸氢二铵的添加浓度区间为10–20 mmol/L时菌丝长势最好。以缺氮时的酶活作为对照,当磷酸氢二铵的添加浓度为10 mmol/L时,羧甲基纤维素酶的活力最强,显著高于对照组(P<0.05);当添加浓度为5 mmol/L时,滤纸纤维素酶的活力最强,显著高于对照组(P<0.05),而10 mmol/L浓度下的酶活力比5 mmol/L时稍有下降,但二者之间无显著性差异(P>0.05);当添加浓度为40 mmol/L时,木聚糖酶的活力最强,显著高于对照组(P<0.05);当添加浓度为10mmol/L时,漆酶的活力最强,显著高于对照组(P<0.05)。基质降解酶...     

The culture of plant cells with ammonium salts as the sole nitrogen source

Soybean cell suspension cultures grew on defined media with ammonium as the sole nitrogen source if Krebs cycle acids were added. Satisfactory growth was obtained with ammonium salts of citrate, malate, fumarate, or succinate, when compared with the regular medium containing nitrate and ammonium. Little or no growth occurred when ammonium salts of shikimate, tartrate, acetate, carbonate, or sulfate were used. The cells also grew well with l-glutamine as nitrogen source. The specific activities of glutamine synthetase and isocitrate dehydrogenase (nicotinamide adenine dinucleotide phosphate) were lower than in cells grown on a nitrate medium, but ammonium enhanced the activity of glutamate dehydrogenase. Cells of soybean, wheat, and flax have been cultured for an extended period on the ammonium citrate medium.     

Metabolism and Synthesis of Indole-3-Acetic Acid (IAA) in Zea mays (Levels of IAA during Kernel Development and the Use of in Vitro Endosperm Systems for Studying IAA Biosynthesis)

Kernels of Zea mays on an intact plant accumulate indole-3-acetic acid (IAA) at the rate of 190 ng g-1 fresh weight h-1. Of the IAA synthesized, 97% is in the esterified form and less than 3% remains as the free acid. The site of biosynthesis of the IAA, whether synthesized in the leaf and transported to the kernel, or in the kernel and remaining in the kernel, has not been established. In an attempt to determine the locus of synthesis, we grew isolated kernels on agar media not containing tryptophan or other possible aromatic precursors of IAA and observed IAA synthesis of 99 ng g-1 fresh weight h-1, approximately 52% of the in situ rate. Thus, the kernel contains all of the enzymes required for de novo aromatic biosynthesis of IAA and its ester conjugates. Furthermore, endosperm cells in suspension culture, grown on hormone-free media and in the absence of aromatic precursors, are able to synthesize IAA at a rate of 9.2 ng g-1 fresh weight h-1, or 4.8% of the in situ rate. This finding establishes that all of the enzymes of IAA biosynthesis occur in the endosperm and that the endosperm is a site of IAA biosynthesis. Isolated endosperm, prepared from developing kernels, synthesized IAA from labeled anthranilate at a rate of 8.6 ng g-1 fresh weight h-1, or 4.5% of the in situ rate. Frozen endosperm preparations maintained the ability to synthesize labeled IAA from labeled anthranilate. The identity of the synthesized IAA was established by mass spectral analysis. We suggest that endosperm preparations of Z. mays are suitable for study of the mechanism(s) of IAA biosynthesis because they (a) have high rates of synthesis; (b) show stability to freezing, enabling enzyme storage; (c) provide a system with a known rate of in situ synthesis; and (d) are available in large amounts for use as an enzyme source.     

The effect of pH on nitrogen supply, cell lysis, and solvent production in fermentations of Clostridium acetobutylicum

In batch fermentations of C. acetobutylicum, with 5 g/L yeast extract and 50mM glucose, the ratio of ammonium to glucose affected solvent production when the pH was left to vary uncontrolled from 4.5 to 3.65. High solvent production was observed for a low ratio. When the pH was controlled at 4.5, only acids were produced for all ratio values. At a low ammonium-to-glucose ratio, solvents were produced when the pH was controlled at 3.7. Acids only were produced for a low ratio value at pH 4.0 or for a high ratio value at pH 3.7. In continuous cultures, mostly acids were produced under glucose limitation, but solvents were produced under nitrogen limitation. It was concluded that the nitrogen availability controls solvent production and that the pH affects the availability of organic nitrogen. Biomass autolysis at the stationary phase of batch cultures was reversibly inhibited at pH values less than 3.8. In batch fermentations, the overall molar growth yields on ATP (Y(ATP)) varied from 5.5 to 9.0 and the transient yields from 5.5 to 15.5. In continuous cultures, the Y(ATP) values varied from 5.5 to 14.7 under glucose limitation, and from 6.1 to 9.3 under nitrogen limitation. The Y(ATP) depended on the ammonium to glucose ratio and the culture pH, but did not show the usual dependence on the specific growth rate in batch cultures. The experiments seem to confirm the hypothesis that solvent production is controlled by the demand and availability of ATP.     

Quantum requirements for growth and fatty acid biosynthesis in the marine diatom Phaeodactylum tricornutum (Bacillariophyceae) in nitrogen replete and limited conditions

We determined the quantum requirements for growth (1/?_μ) and fatty acid (FA) biosynthesis (1/?_FA) in the marine diatom, Phaeodactylum tricornutum, grown in nutrient replete conditions with nitrate or ammonium as nitrogen sources, and under nitrogen limitation, achieved by transferring cells into nitrogen free medium or by inhibiting nitrate assimilation with tungstate. A treatment in which tungstate was supplemented to cells grown with ammonium was also included. In nutrient replete conditions, cells grew exponentially and possessed virtually identical 1/?_μ of 40–44 mol photons · mol C^?1. In parallel, 1/?_FA varied between 380 and 409 mol photons · mol C^?1 in the presence of nitrate, but declined to 348 mol photons · mol C^?1 with ammonium and to 250 mol photons · mol C^?1 with ammonium plus tungstate, indicating an increase in the efficiency of FA biosynthesis relative to cells grown on nitrate of 8% and 35%, respectively. While the molecular mechanism for this effect remains poorly understood, the results unambiguously reveal that cells grown on ammonium are able to direct more reductant to lipids. This analysis suggests that when cells are grown with a reduced nitrogen source, fatty acid biosynthesis can effectively become a sink for excess absorbed light, compensating for the absence of energetically demanding nitrate assimilation reactions. Our data further suggest that optimal lipid production efficiency is achieved when cells are in exponential growth, when nitrate assimilation is inhibited, and ammonium is the sole nitrogen source.     

Carbon and nitrogen source nutrition of fumagillin biosynthesis by Aspergillus fumigatus

The carbon and nitrogen source requirements of Aspergillus fumigatus NRRL 2436 for growth and production of the angiogenesis inhibitor fumagillin were studied in chemically defined media. Both carbon and nitrogen sources strongly influenced fumagillin formation. Two out of 29 carbon sources tested interfered with fumagillin biosynthesis. The best combination of two carbon sources was 30 g L(-1) xylan and 50 g L(-1) mannose. Of fifteen nitrogen sources tested, three ammonium salts (chloride, sulfate, and dibasic phosphate) failed to support fumagillin formation, presumably due to the low pH which developed. The dosage-response study of the best nitrogen source, L-glutamic acid, revealed that 9 g L(-1) was optimal. Volumetric production of fumagillin was increased by 15-fold over that in the starting (Peterson-Goldstein) medium as a result of these findings.     

Growth and embryo formation in wild-carrot suspension cultures with ammonium ion as a sole nitrogen source.

Wild-carrot (Daucus carota L.) suspension cultures grew and produced embryos on ammonium ion as a sole source of nitrogen in the absence of any exogenous Kreb's cycle acid when the pH of the medium was controlled by continuous titration with with KOH or KHCO3.     

Production of methionine and glutamic acid from η-alkanes bySerratia marcescens var.kiliensis

A hydrocarbon-utilizing Serratia marcescens var. kiliensis grew and accumulated methionine and glutamic acid in a synthetic medium with hydrocarbon as sole carbon source. n-Hexadecane and ammonium phosphate were found as the most suitable carbon and nitrogen sources, respectively. Optimum pH for growth and methionine production was 7.2, and that for glutamic acid accumulation was 7.4. Yeast extract significantly stimulated growth and amino acid production and could be substituted by cyanocobalamine. Benzylpenicillin, Tween 80, SDS or EDTA did not increase amino acid production. Under optimal cultural conditions in the laboratory the organism produced 1.68 g of glutamic acid and 0.78 g of methionine per litre.