Long‐term nitrogen loading alleviates phosphorus limitation in terrestrial ecosystems

Increased human‐derived nitrogen (N) deposition to terrestrial ecosystems has resulted in widespread phosphorus (P) limitation of net primary productivity. However, it remains unclear if and how N‐induced P limitation varies over time. Soil extracellular phosphatases catalyze the hydrolysis of P from soil organic matter, an important adaptive mechanism for ecosystems to cope with N‐induced P limitation. Here we show, using a meta‐analysis of 140 studies and 668 observations worldwide, that N stimulation of soil phosphatase activity diminishes over time. Whereas short‐term N loading (≤5 years) significantly increased soil phosphatase activity by 28%, long‐term N loading had no significant effect. Nitrogen loading did not affect soil available P and total P content in either short‐ or long‐term studies. Together, these results suggest that N‐induced P limitation in ecosystems is alleviated in the long‐term through the initial stimulation of soil phosphatase activity, thereby securing P supply to support plant growth. Our results suggest that increases in terrestrial carbon uptake due to ongoing anthropogenic N loading may be greater than previously thought.     

天然产物中五元杂环生物合成过程的研究进展

五元杂环是指一类含有除碳以外的杂原子的五元环有机化合物,可分为含有一个杂原子的杂环和含有两个杂原子的五元杂环。杂原子通常为氮原子、氧原子或硫原子,在成环时符合休克尔(Hückel)规则,具有芳香性。五元杂环以独特的生物学特性和参与氢键相互作用的能力,成为天然化合物发挥活性功能的重要基团。五元杂环在不同的生物合成途径中有多种环化过程,其前体可以是天然氨基酸、乙酸及乙酰辅酶A等多种形式。将从吡咯、恶唑和噻唑三种五元杂环入手,以代表性化合物为例,对其在生命体中生物合成过程的成环过程进行探讨,为组合生物合成和未知化合物中五元杂环成环过程的研究提供参考。     

Heat shock phenomena in Chironomus tentans

Incubation of 4th instar larvae of Chironomus tentans at elevated temperatures leads in salivary and Malpighian chromosomes to the appearance of 4–5 new puffs. Previously present puffs, particularly Balbiani rings in salivary chromosomes, become drastically reduced. The reactions of region IV-5C and Balbiani ring 1 and 2 in salivary glands are quantitatively analyzed. Statistically significant heat shock effects are observed already after 5 min and reach a maximum between 30 and 60 min. The effective temperature range is small (between 33 to 40 ° C) with an optimum at 37 ° C. Above 40 ° C, i.e., at overheat shock temperatures, heat shock reactions are suppressed. Larvae heat or overheat shocked for 1–7 h or 15–30 min, respectively, survive when returned to normal culturing temperatures. The recovery from heat shock of the puffing pattern occurs in two phases: a fast one (10–20 min) and a slow one (up to 5 h) sometimes separated by a period of backlash. Quenching of overheat shocked larvae does not result in a delayed heat shock reaction.     

Effect of osmotic shock on tetracycline resistance in Escherichia coli bearing an R-factor

1. Escherichia coli with an R-factor conferring resistance to tetracycline was induced to high-degree resistance by pre-exposure to the antibiotic. The degree of resistance was drastically lowered by subjecting the cells to osmotic shock. 2. Resistance to tetracycline was rapidly restored by incubating the shocked cells in a glucose-salts medium containing shock proteins prepared from tetracycline-sensitive and -resistant cells. Resistance was also restored by incubating the cells in a complex medium without shock protein. 3. The initial recovery of resistance was followed by a secondary fall in resistance when the cells were cultured in complex medium; this secondary fall was largely prevented by the addition of a low concentration (10mug/ml) of tetracycline to cells. The secondary fall was significantly less in shocked E. coli cells harbouring a mutant R-factor in which tetracycline resistance is largely constitutive. 4. Tetracycline resistance was also transiently depressed by treating R-factor-bearing cells with EDTA in tris buffer. 5. The significance of these results in relation to the mechanism of tetracycline resistance in R-factor-bearing cells is discussed.     

Factors Affecting Nitrous Oxide Production: A Comparison of Biological Nitrogen Removal Processes with Partial and Complete Nitrification

Nitrous oxide (N₂O) emission from biological nitrogen removal (BNR) processes has recently received more research attention. In this study, two lab-scale BNR systems were used to investigate the effects of various operating parameters including the carbon to nitrogen (C/N) ratio, ammonia loading, and the hydraulic retention time on N₂O production. The first system was operated in a conventional BNR mode known as the Ludzack–Ettinger (LE) process, consisting of complete denitrification and nitrification reactors, while the second one was operated in a shortcut BNR (SBNR) mode employing partial nitrification and shortcut denitrification, which requires less oxygen and carbon sources. As the C/N ratio was decreased, a significant increase in N₂O production was observed only in the anoxic reactor of the LE process, indicating that N₂O was released as an intermediate of the denitrification reaction under the carbon-limited condition. However, the SBNR process did not produce significant N₂O even at the lowest C/N ratio of 0.5. When the SBNR process was subjected to increasing concentrations of ammonia, N₂O production from the aerobic reactor was rapidly increased. Furthermore, the increasing production of N₂O was observed mostly in the aerobic reactor of the SBNR process with a decline in hydraulic retention time. These experimental findings indicated that the increase in N₂O production was closely related to the accumulation of free ammonia, which was caused by an abrupt increase of the ammonium loading. Consequently, the partial nitrification was more susceptible to shock loading conditions, resulting in a high production of N₂O, although the SBNR process was more efficient with respect to nitrogen removals as well as carbon and oxygen requirements.     

Specific oxygen, ammonia, and nitrate uptake rates of a biological nutrient removal process treating elevated salinity wastewater

Anaerobic/anoxic/aerobic systems inoculated without and with NaCl acclimated cultures, i.e., Models A and B, respectively, were fed with a synthetic wastewater at various salinity levels. After achieving a steady state, the systems were shocked with 70 g/l NaCl for four consecutive days before returning to pre-shock conditions. At the steady-state, the specific oxygen uptake rates (SOURs) increased with an increase of sodium chloride concentration (from 5.40 to 9.72 mg O₂/g mixed liquor suspended solids (MLSS)-h at 0–30 g/l NaCl for Model A and from 6.84 to 17.64 mg O₂/g MLSS-h at 5–30 g/l NaCl for Model B). In contrast, the specific ammonia uptake rate (SAUR) and specific nitrate uptake rate (SNUR) decreased with increasing chloride concentration (from 4.76 to 2.14 mg NH₃–N/g MLSS-h and 2.50 to 1.22 NO3–N/g MLSS-h, for Model A, and from 3.84 to 2.71 mg NH₃–N/g MLSS-hr and 2.54 to 1.82 mg NO₃–N/g MLSS-hr, for Model B). During the shocked period, the SOUR in most scenarios increased whereas the SAUR and SNUR tended to decrease. The impact of the chloride shock on nitrifiers was more obvious than on denitrifiers; however, after a certain recovery period, the activities of both nitrifiers and denitrifiers in terms of SAUR and SNUR were approximately the same as those prior to shock.     

Transport of gamma-butyrobetaine in an Agrobacterium species isolated from soil.

An Agrobacterium sp. isolated from soil by selective growth on gamma-butyrobetaine (gamma-trimethylaminobutyrate) as the sole source of both carbon and nitrogen has been shown to possess an inducible transport system for this growth substrate. This transport system has a Kt of 0.5 microM and a maximal velocity of 3.8 nmol/min per mg (dry weight). The influx of gamma-butyrobetaine is optimal at pH 8.5 and operates against a concentration gradient. The transport system shows a high specificity for trimethylamine carboxylic acid molecules of defined chain length. gamma-Butyrobetaine uptake was significantly reduced in osmotically shocked cells and a gamma-butyrobetaine binding activity was detected in the crude shock fluid. This suggests a transport mechanism involving a periplasmic gamma-butyrobetaine binding protein.     

Synthesis of heat shock proteins in Cf124 cells: Effect of virus infection

The transient synthesis of a class of proteins known as heat shock or stress response proteins was induced when Cf124 cells were incubated at high temperature. When cells were infected with Chilo iridescent virus and simultaneously heat shocked, heat shock protein (hsp) synthesis was delayed, and the shut-off of hsp synthesis was suppressed. In previously heat shocked cells, inhibition of hsp synthesis was dependent upon the multiplicity of infection, however, when infection preceded heat shock, the synthesis of hsp started immediately after heat shock. In all cases, hsp synthesis was dependent upon newly synthesized messenger RNA.     

Structural insights into the specific recognition of N‐heterocycle biodenitrogenation‐derived substrates by microbial amide hydrolases

N‐heterocyclic compounds from industrial wastes, including nicotine, are environmental pollutants or toxicants responsible for a variety of health problems. Microbial biodegradation is an attractive strategy for the removal of N‐heterocyclic pollutants, during which carbon–nitrogen bonds in N‐heterocycles are converted to amide bonds and subsequently severed by amide hydrolases. Previous studies have failed to clarify the molecular mechanism through which amide hydrolases selectively recognize diverse amide substrates and complete the biodenitrogenation process. In this study, structural, computational and enzymatic analyses showed how the N‐formylmaleamate deformylase Nfo and the maleamate amidase Ami, two pivotal amide hydrolases in the nicotine catabolic pathway of Pseudomonas putida S16, specifically recognize their respective substrates. In addition, comparison of the α‐β‐α groups of amidases, which include Ami, pinpointed several subgroup‐characteristic residues differentiating the two classes of amide substrates as containing either carboxylate groups or aromatic rings. Furthermore, this study reveals the molecular mechanism through which the specially tailored active sites of deformylases and amidases selectively recognize their unique substrates. Our work thus provides a thorough elucidation of the molecular mechanism through which amide hydrolases accomplish substrate‐specific recognition in the microbial N‐heterocycles biodenitrogenation pathway.     

Defensive burying: Effects of diazepam and oxprenolol measured in extinction

When a rat is shocked via a prod in a chamber with sawdust on the floor it will typically push the flooring material with snout and forepaws towards and over the prod. We administered diazepam (.5 and 1.0 mg/kg) and oxprenolol (10 and 20 mg/kg) the day following shock exposure, and observed the complete suppression of burying by diazepam, and some suppression with oxprenolol. These effects are independent of interference with initial association of shock and prod, and of changes in general activity.     

Effect of prior heat shock on heat resistance of Listeria monocytogenes in meat.

The effect of prior heat shock on the thermal resistance of Listeria monocytogenes in meat was investigated. A sausage mix inoculated with approximately 10(7) L. monocytogenes per g was initially subjected to a heat shock temperature of 48 degrees C before being heated at a final test temperature of 62 or 64 degrees C. Although cells heat shocked at 48 degrees C for 30 or 60 min did not show a significant increase in thermotolerance as compared with control cells (non-heat shocked), bacteria heat shocked for 120 min did, showing an average 2.4-fold increase in the D64 degrees C value. Heat-shocked cells shifted to 4 degrees C appeared to maintain their thermotolerance for at least 24 h after heat shock.     

Activity of enzymatic antioxidant defense systems in chilled and heat shocked cucumber seedling radicles

Chilling whole cucumber seedlings that had 10‐mm long radicles for 4 days at 2.5°C significantly inhibited subsequent radicle growth both by increasing the time it took the seedlings to recover from chilling and attain a linear rate of radicle growth, and by decreasing the subsequent rate of linear growth. Exposing cucumber seedlings to 45°C for up to 20 min had no effect on subsequent radicle growth, while longer exposures produced reductions in growth. A heat shock at 45°C for 10 min induced the optimal protection to 4 days of chilling at 2.5°C by reducing chilling inhibition from 60 to 42%. Two hours after being chilled, heat shocked or heat shocked and then chilled, there was no difference in protein content of the apical 1 cm of the seedling radicle among these treatments and the non‐heat shocked, non‐chilled control. Two days after treatment, the protein content was still similar in tissue that had been heat shocked or heat shocked and chilled, while it was significantly reduced in tissue that had been chilled. In general, 2 h after treatment, the activity of the 5 antioxidant enzymes examined in this study [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPX; EC 1.11.1.7) and glutathione reductase (GR; EC 1.6.4.2)] were reduced by chilling and unaffected or increased by heat shock. When heat shock was followed by chilling, there was a consistent effect of the heat shock treatment on preventing the loss of enzyme activity following chilling. This protective effect of the heat shock treatment was even more pronounced after 2 days of recovery at 25°C for SOD, CAT and APX. In contrast, the activity of GR and GPX was substantially higher in chilled tissue than in tissue that had been heat shocked before being chilled. Elevated levels of GR and GPX therefore appear to be correlated with the development of chilling injury, while elevated levels of SOD, CAT and APX appear to be correlated with the development of heat shock‐induced chilling tolerance.     

On Photosynthesis and Organic Carbon, Carbon Dioxide, and Oxygen Flows in the Ocean

The modern concept of photosynthesis as a mechanism for utilizing the energy of solar radiation is used as the basis for assessing the scale of photosynthetic production of initial organic matter in the ocean (primary biological production), its destruction, the carbon and carbon dioxide cycles (flows) involved in this process, and the size of oil- and gas-bearing hydrocarbonaceous formations originating in sedimentary deposits.     

Effect of prior heat shock on heat resistance of Listeria monocytogenes in meat

The effect of prior heat shock on the thermal resistance of Listeria monocytogenes in meat was investigated. A sausage mix inoculated with approximately 10(7) L. monocytogenes per g was initially subjected to a heat shock temperature of 48 degrees C before being heated at a final test temperature of 62 or 64 degrees C. Although cells heat shocked at 48 degrees C for 30 or 60 min did not show a significant increase in thermotolerance as compared with control cells (non-heat shocked), bacteria heat shocked for 120 min did, showing an average 2.4-fold increase in the D64 degrees C value. Heat-shocked cells shifted to 4 degrees C appeared to maintain their thermotolerance for at least 24 h after heat shock.     

Efficient guanylation of aromatic and heterocyclic amines catalyzed by cyclopentadienyl-free rare earth metal amides

Diamido-supported rare earth metal amides with the general formula {(CH₂SiMe₂)[(2,6-ⁱPr₂C₆H₃)N]₂}LnN(SiMe₃)₂(THF) [(Ln = Yb(1), Y(2), Dy(3), Sm (4), Nd (5)] were found to be highly efficient catalysts for the guanylation of both aromatic and heterocyclic amines under mild conditions. It is found that these catalysts are compatible with a wide range of substituents such as ⁱPr, Me, and MeO having electron-donating property and substituents such as Cl, Br, and O₂N having electron-withdrawing property on the aromatic rings of the aromatic or the heterocyclic amines. The methodology has also the advantages of easy preparation of the catalysts, quick conversion of the substrates to products, mild reaction conditions, and low catalyst loading.     

Heat shock inhibits caspase‐1 activity while also preventing its inflammasome‐mediated activation by anthrax lethal toxin

Anthrax lethal toxin (LT) rapidly kills macrophages from certain mouse strains in a mechanism dependent on the breakdown of unknown protein(s) by the proteasome, formation of the Nalp1b (NLRP1b) inflammasome and subsequent activation of caspase‐1. We report that heat‐shocking LT‐sensitive macrophages rapidly protects them against cytolysis by inhibiting caspase‐1 activation without upstream effects on LT endocytosis or cleavage of the toxin's known cytosolic substrates (mitogen‐activated protein kinases). Heat shock protection against LT occurred through a mechanism independent of de novo protein synthesis, HSP90 activity, p38 activation or proteasome inhibition and was downstream of mitogen‐activated protein kinase cleavage and degradation of an unknown substrate by the proteasome. The heat shock inhibition of LT‐mediated caspase‐1 activation was not specific to the Nalp1b (NLRP1b) inflammasome, as heat shock also inhibited Nalp3 (NLRP3) inflammasome‐mediated caspase‐1 activation in macrophages. We found that heat shock induced pro‐caspase‐1 association with a large cellular complex that could prevent its activation. Additionally, while heat‐shocking recombinant caspase‐1 did not affect its activity in vitro, lysates from heat‐shocked cells completely inhibited recombinant active caspase‐1 activity. Our results suggest that heat shock inhibition of active caspase‐1 can occur independently of an inflammasome platform, through a titratable factor present within intact, functioning heat‐shocked cells.     

Effect of heat shock on the metabolism of glutathione in maize roots

High performance liquid chromatography analyses revealed that glutathione (GSH) and cysteine are two of the major low molecular weight thiol compounds in maize root extracts. Treatment of maize roots to heat shock temperatures of 40°C resulted in a decrease of cysteine levels and an increase of GSH levels. Pulse labeling of maize roots with [³⁵S]cysteine showed that the rate of incorporation of ³⁵S into GSH or glutathione disulfide (GSSG) in heat shocked tissues was twice that in nonheat shocked tissues. In addition, extracts from heat shocked maize, barley, and soybean tissues contained an unidentified low molecular weight compound that increased from 1.2- to 8-fold within 2 hours of heat shock treatment depending on the tissue and plant involved. Our results indicate that during heat shock there is an increase in the activity of the GSH synthetizing capacity in maize root cells. The elevated synthesis of GSH may be related to the cells capacity to cope with heat stress conditions.     

Effect of organic carbon shock loading on endogenous denitrification in sequential batch reactors

This work was focused on the performance evaluation of sequential batch reactors (SBR) treating sewage, through a process of endogenous biological denitrification. Different operational conditions were carried out, and the behaviour under the effects of organic shock loading was examined. Three laboratory scale reactors were operated simultaneously and fed with similar wastewater. The substratum was molasses and nitrate, as carbon and nitrogen sources, respectively. The three reactors were operated during different aeration periods (0, 15 and 30 min). Sudden changes (shock loading) in organic matter concentration were performed during the experiment. Thus, influent load was quickly increased threefold in relation to the original concentration. Results indicated that SBR reactors withstand adequately moderate shock loading. With regard to substratum degradation, nitrate elimination achieved was approximately 80%, while denitrification rate was approximately 0.87 mgg(-1)h(-1).     

Cell-specific association of heat shock-induced proton flux with actin ring formation in Chenopodium cells: comparison of auto- and heterotroph cultures

A comparison of the responses of extracellular pH, buffering capacity and actin cytoskeleton in autotroph and heterotroph Chenopodium rubrum cells to heat shock revealed cell-specific reactions: alkalinization caused by the heat shock at 25-35 degrees C was higher in heterotroph cells and characterized by heat shock-induced changes in the actin cytoskeleton and ring formation at 35-37 degrees C. Rings (diameter up to 3 mum) disappeared and extracellular pH recovered after the heat-shocked cells were transferred into control medium. At 41 degrees C, no rings but a network of coarse actin filaments were induced; at higher temperatures, fragmentation of the actin cytoskeleton and release of buffering compounds occurred, indicating sudden membrane leakage at 45-47 degrees C. The calcium chelator EGTA [ethylene-glycol-bis(beta-aminoethyl-ether)-N,N,N',N'-tetraacetic-acid] increased the frequency of heat shock-induced rings. Ionophore (10 microM nigericin) and the sodium/proton antiport blocker [100 microM 5-(N-ethyl-N-isopropyl)-amiloride] mimicked the effect of the 37 degrees C heat shock. The cytoskeleton inhibitors latrunculin B, cytochalasin D and 2,3-butanedione monoxime inhibited ring formation but not alkalinization. In autotroph cells, the treatment with nigericin (10 microM) produced rings, although the actin cytoskeleton was not affected by temperatures up to 45 degrees C. We conclude that Chenopodium cells express a specific temperature sensor that has ascendancy over the organization of the actin cytoskeleton; this is probably a temperature- and potential-sensitive proton-transporting mechanism that is dependent on the culture conditions of the heterotroph cells.