Methanobactin, a copper-acquisition compound from methane-oxidizing bacteria

Siderophores are extracellular iron-binding compounds that mediate iron transport into many cells. We present evidence of analogous molecules for copper transport from methane-oxidizing bacteria, represented here by a small fluorescent chromopeptide (C45N12O14H62Cu, 1216 daltons) produced by Methylosinus trichosporium OB3b. The crystal structure of this compound, methanobactin, was resolved to 1.15 angstroms. It is composed of a tetrapeptide, a tripeptide, and several unusual moieties, including two 4-thionyl-5-hydroxy-imidazole chromophores that coordinate the copper, a pyrrolidine that confers a bend in the overall chain, and an amino-terminal isopropylester group. The copper coordination environment includes a dual nitrogen- and sulfur-donating system derived from the thionyl imidazolate moieties. Structural elucidation of this molecule has broad implications in terms of organo-copper chemistry, biological methane oxidation, and global carbon cycling.     

Soluble and colloidal iron in the oligotrophic North Atlantic and North Pacific

In the oligotrophic North Atlantic and North Pacific, ultrafiltration studies show that concentrations of soluble iron and soluble iron-binding organic ligands are much lower than previously presumed "dissolved" concentrations, which were operationally defined as that passing through a 0.4-micrometer pore filter. Our studies indicate that substantial portions of the previously presumed "dissolved" iron (and probably also iron-binding ligands) are present in colloidal size range. The soluble iron and iron-binding organic ligands are depleted at the surface and enriched at depth, similar to distributions of major nutrients. By contrast, colloidal iron shows a maximum at the surface and a minimum in the upper nutricline. Our results suggest that "dissolved" iron may be less bioavailable to phytoplankton than previously thought and that iron removal through colloid aggregation and settling should be considered in models of the oceanic iron cycle.     

大豆蛋白水解物铁结合能力的测定研究

利用蛋白酶对大豆分离蛋白进行催化水解．并得到了水解程度不同的两种蛋白水解物，通过向水解物溶液中加入过量的Ｆｅ３＋，对利用硫氰酸盐比色法确定低肽分子的铁结合能力进行了初步的规定及探讨．发现这两种高度水解的蛋白质其肽分子的铁结合能力与其浓度无关．与其水解程度的关系也不太大．     

Heat flux anomalies in Antarctica revealed by satellite magnetic data

The geothermal heat flux is an important factor in the dynamics of ice sheets; it affects the occurrence of subglacial lakes, the onset of ice streams, and mass losses from the ice sheet base. Because direct heat flux measurements in ice-covered regions are difficult to obtain, we developed a method that uses satellite magnetic data to estimate the heat flux underneath the Antarctic ice sheet. We found that the heat flux underneath the ice sheet varies from 40 to 185 megawatts per square meter and that areas of high heat flux coincide with known current volcanism and some areas known to have ice streams.     

Effects of climatic warming on lakes of the central boreal forest

Twenty years of climatic, hydrologic, and ecological records for the Experimental Lakes Area of northwestern Ontario show that air and lake temperatures have increased by 2 degrees C and the length of the ice-free season has increased by 3 weeks. Higher than normal evaporation and lower than average precipitation have decreased rates of water renewal in lakes. Concentrations of most chemicals have increased in both lakes and streams because of decreased water renewal and forest fires in the catchments. In Lake 239, populations and diversity of phytoplankton also increased, but primary production showed no consistent trend. Increased wind velocities, increased transparency, and increased exposure to wind of lakes in burned catchments caused thermoclines to deepen. As a result, summer habitats for cold stenothermic organisms like lake trout and opposum shrimp decreased. Our observations may provide a preview of the effects of increased greenhouse warming on boreal lakes.     

Control of nitrogen export from watersheds by headwater streams

A comparative (15)N-tracer study of nitrogen dynamics in headwater streams from biomes throughout North America demonstrates that streams exert control over nutrient exports to rivers, lakes, and estuaries. The most rapid uptake and transformation of inorganic nitrogen occurred in the smallest streams. Ammonium entering these streams was removed from the water within a few tens to hundreds of meters. Nitrate was also removed from stream water but traveled a distance 5 to 10 times as long, on average, as ammonium. Despite low ammonium concentration in stream water, nitrification rates were high, indicating that small streams are potentially important sources of atmospheric nitrous oxide. During seasons of high biological activity, the reaches of headwater streams typically export downstream less than half of the input of dissolved inorganic nitrogen from their watersheds.     

几种酚类化合物在黄河水体沉积物上吸附行为的实验研究

采用现场采集河底表层沉积物及室内分析的方法,研究了邻硝基苯酚、对硝基苯酚、2,4-二硝基苯酚、2,4-二氯苯酚、五氯酚等酚类化合物在黄河水体沉积物上的吸附行为。结果表明,邻硝基苯酚等酚类化合物在黄河水体沉积物上的吸附量随pH值的增大而减小;随着离子强度的增加,对硝基苯酚和邻硝基苯酚在黄河水体沉积物上的吸附量增加;沉积物的有机质含量是影响酚类化合物吸附量大小的一个重要因素,即溶解分配过程在黄河水体沉积物吸附酚类化合物中起重要作用;当表面活性剂SDBS存在时,酚类化合物在黄河水体沉积物上的吸附以分配作用为主,SDBS在所测定的浓度范围内(小于CMC),酚类化合物的沉积物-水分配系数均增大,分配系数的增大倍数与它们的辛醇-水分配系数KOW成正相关。     

宋代農田水利的開發

宋代興修農田水利主要方面可分為四大項:一、利用河北淀泊開闢稻田,二、利用東南窪地修築圩田,三、引濁放淤,改良鹽鹼土地,四、修復古渠舊堰,以利灌溉。這些都是具有一定的基礎和原因,也都在農業生產上獲得成績,因而促進了經濟的發展。現在我們正在執行發展國民經濟的第一個五年計劃,其中有"積極興修農田水利"的規定。古人說"温故而知新",為由歷史上找出發展的道路起見,特寫此短篇,聊供設計時的參考。     

Acid rain: neutralization within the hubbard brook ecosystem and regional implications

The neutralization of strong acids from precipitation is largely accomplished (75 percent) in the soil zone by rapid reaction with basic aluminum salts and biologic matter. On a regional basis, acidified and aluminum-rich lakes and streams in New England are confined mainly to low-order watersheds.     

Freshwater ferromanganese concretions: chemistry and internal structure

Studies by optical microscopy, x-ray diffraction, and electron probe techniques of ferromanganese concretions from three Canadian lakes reveal chemical banding of amorphous hydrated iron and manganese oxides. The average ratio of iron to manganese in concretions from these lakes varies from 0.43 to 2.56. The concentrations of cobalt, nickel, copper, and lead are one to two orders of magnitude below those reported for oceanic ferromanganese concretions.     

鱼血清转铁蛋白对嗜水气单胞菌的抗性研究

嗜水气单胞菌(Aeromonas hydrophila)在铁限制培养基(M70-Fe)中培养,并用铬天青S(CAS)方法分析,不能产生可检测的含铁细胞;培养两周后,该菌在蓝色的琼脂培养基上产生围绕细菌菌落的清晰的橘黄色晕轮。但在鲫鱼血清中培养36h后,便达到了对数生长期。表明嗜水气单胞菌依靠夺取血清中的铁,可以正常生长;而在铁限制培养时,则难以存活。以细菌胞外蛋白酶消化鱼类血清,并在聚丙烯酰胺凝胶电泳(PAGE)后进行原位铁结合试验,结果表明：嗜水气单胞菌胞外蛋白酶只能通过降解血清中转铁蛋白以外的含铁蛋白来补偿含铁细胞中的铁,而含铁转铁蛋白和脱铁转铁蛋白均不能被胞外蛋白酶消化,仍有很强的铁结合能力。     

Disease-suppressive soil and root-colonizing bacteria

Soils in many areas suppress certain plant diseases. Understanding the basis for this disease suppressiveness could lead to improved plant health in less favorable areas. Some forms of disease suppression may be caused by bacteria in the genus Pseudomonas which aggressively colonize root surfaces. Increased plant growth and yield are closely associated with the capacity of some of these bacteria to produce iron-binding compounds called siderophores. This article addresses the biological characteristics of these soil-bome root epiphytes, their contribution to plant health, and their potential use in biotechnology.     

Frataxin acts as an iron chaperone protein to modulate mitochondrial aconitase activity

Numerous degenerative disorders are associated with elevated levels of prooxidants and declines in mitochondrial aconitase activity. Deficiency in the mitochondrial iron-binding protein frataxin results in diminished activity of various mitochondrial iron-sulfur proteins including aconitase. We found that aconitase can undergo reversible citrate-dependent modulation in activity in response to pro-oxidants. Frataxin interacted with aconitase in a citrate-dependent fashion, reduced the level of oxidant-induced inactivation, and converted inactive [3Fe-4S]1+ enzyme to the active [4Fe-4S]2+ form of the protein. Thus, frataxin is an iron chaperone protein that protects the aconitase [4Fe-4S]2+ cluster from disassembly and promotes enzyme reactivation.     

Acidic mine drainage: the rate-determining step

The rate-determining step in the oxidation of iron pyrite and the formation of acidity in streams associated with coal and copper mines is the oxidation of ferrous iron. Effective pollution abatement necessitates control ling this reaction.     

Freshwater methane emissions offset the continental carbon sink

Inland waters (lakes, reservoirs, streams, and rivers) are often substantial methane (CH(4)) sources in the terrestrial landscape. They are, however, not yet well integrated in global greenhouse gas (GHG) budgets. Data from 474 freshwater ecosystems and the most recent global water area estimates indicate that freshwaters emit at least 103 teragrams of CH(4) year(-1), corresponding to 0.65 petagrams of C as carbon dioxide (CO(2)) equivalents year(-1), offsetting 25% of the estimated land carbon sink. Thus, the continental GHG sink may be considerably overestimated, and freshwaters need to be recognized as important in the global carbon cycle.     

Forest fire: effects on phosphorus movement to lakes

After a wildfire in the virgin forest of a lake-watershed region in northeastern Minnesota, the phosphorus concentration in the runoff was elevated for 2 years and decreased in the third year. However, there was no increase in the phosphorus concentrations of a lake and its input stream. This indicates that, under similar circumstances, controlled burning will not damage streams or lakes by elevating phosphorus levels.     

南方红壤处理滇池水的初步试验

以含磷极低、富含铁铝氧化物、对磷具有较强的吸附和固定能力的南方红壤为材料，用该土壤对滇池水进行了去磷效果的初步试验。结果表明，该土壤对水体磷的去除效果较好，但去除效果与土壤加入量、处理中的振荡时间、振荡强度及水体的理化性质相关。模拟结果表明，有效处理土壤或选用理想的材料，可以更好地去除水体磷。     

Effects of Acid rain on freshwater ecosystems

Acid-vulnerable areas are more numerous and widespread than believed 7 years ago. Lakes and streams in acid-vulnerable areas of northeastern North America have suffered substantial declines in acid-neutralizing capacity, the worst cases resulting in biological damage. Many invertebrates are very sensitive to acidification, with some disappearing at pH values as high as 6.0. However, the recent rate of acidification of lakes is slower than once predicted, in part the result of decreases in sulfur oxide emissions. A discussion of some of the processes that have contributed to the acidification of lakes as well as those that have protected acid-sensitive freshwaters is presented. The author is in the Department of Fisheries and Oceans, Freshwater Institute, 501 University Crescent, Winnipeg, Manitoba R3T 2N6, Canada.     

Phytic Acid Contents of Wheat Flours from Different Mill Streams

The phytic acid contents of eight fractions of wheat flours from different mill streams and those in wheat brans, which were separated by different sieves into various sizes, were determined and analyzed. A rapid method for phytic acid assay by adding thioglycolic acid （mercapto acetic acid） with 2,2-bipyridine was used, with an acidic iron-Ⅲ-solution of known iron content. The amount ofphytate was indicated by the decrease in iron in the supernatant. Significant differences were observed in phytic acid content among different milling streams and different cultivars （P〈0.05）. On an average, coarse bran had the highest phytic acid content （53.85 mg g^-1）, and the shorts had 28.48 mg g^-1. The B5 break flour had a higher phytic acid content （4.8 mg g^-1） than the B7 （2.75 mg g^-1） and B8 （2.03 mg g^-1） reduction flours. Lower values were found in the B3, B6 and B7 flours （1.07, 0.79, and 0.76 mg g^-1, respectively）. The phytic acid contents of bran decreased with smaller bran sizes, ranging from 54 to 5.09 mg g^-1.     

Synthesis of ammonium cyanate and urea by reduction of nitric oxide on platinum, rhodium, and ruthenium catalysts

Nearly quantitative conversion of nitric oxide (NO) into N(2)H(4)CO has been obtained in the reduction of NO with carbon monoxide and hydrogen over platinum and rhodium catalysts. Depending on the temperature of collection, N(2)H(4)CO is isolated as ammonium cyanate or its isomer, urea. The process is an effective way of recovering fixed nitrogen from dilute industrial streams containing NO. Ammonium cyanate may play a role in the reduction of NO in automotive exhaust control.