Drei neue Nickelenzyme aus anaeroben Bakterien

Until recently nickel was not considered to be an element of biological importance. Nutritional studies have shown, however, that many eucaryotic and procaryotic organisms are dependent on the transition metal for growth. Four enzymes are presently known to contain nickel: urease from plants and from bacteria; methyl CoM reductase from methanogenic bacteria; all “uptake” hydrogenases investigated so far; and carbon monoxide dehydrogenase from anaerobic bacteria. The prosthetic group of the methyl CoM reductase has been identified as a nickel tetrapyrrole, the structure of which has been elucidated.     

Residual soil nitrate after potato harvest

Nitrogen loss by leaching is a major problem, particularly with crops requiring large amounts of N fertilizer. We evaluated the effect of N fertilization and irrigation on residual soil nitrate following potato (Solanum tuberosum L.) harvests in the upper St-John River valley of New Brunswick, Canada. Soil nitrate contents were measured to a 0.90-m depth in three treatments of N fertilization (0, 100, and 250 kg N ha(-1)) at two on-farm sites in 1995, and in four treatments of N fertilization (0, 50, 100, and 250 kg N ha(-1)) at four sites for each of two years (1996 and 1997) with and without supplemental irrigation. Residual soil NO3-N content increased from 33 kg NO3-N ha(-1) in the unfertilized check plots to 160 kg NO3-N ha(-1) when 250 kg N ha(-1) was applied. Across N treatments, residual soil NO3-N contents ranged from 30 to 105 kg NO3-N ha(-1) with irrigation and from 30 to 202 kg NO3-N ha(-1) without irrigation. Residual soil NO3-N content within the surface 0.30 m was related (R2 = 0.94) to the NO3-N content to a 0.90-m depth. Estimates of residual soil NO3-N content at the economically optimum nitrogen fertilizer application (Nop) ranged from 46 to 99 kg NO3-N ha(-1) under irrigated conditions and from 62 to 260 kg NO3-N ha(-1) under nonirrigated conditions, and were lower than the soil NO3-N content measured with 250 kg N ha(-1). We conclude that residual soil NO3-N after harvest can be maintained at a reasonable level (<70 kg NO3-N ha(-1)) when N fertilization is based on the economically optimum N application.     

Determination of metal and organometal trophic bioaccumulation in the benthic macrofauna of the Adour estuary coastal zone (SW France, Bay of Biscay)

A multidisciplinary approach has been adopted in order to investigate the bioaccumulation of metals and organometals in macrobenthic populations. A complete method coupling a sampling strategy and classification of benthic organisms with a performant analytical procedure for the analysis of both metals and organometals has been developed. A single sample preparation method using a TMAH extraction and species specific isotope dilution makes it possible to analyse metals and organometals in the same extract, which is especially interesting for situations where only a limited amount of sample is available. Low detection limits have been obtained in the range of 12-250 pg g(-1) for mercury and butyltin compounds and 0.4-50 ng g(-1) for metals with good precision (1-10% RSD) even for a very low mass of sample (0.02 g). This method has been applied for monitoring contamination and bioaccumulation of metals and organometals as well as the biodiversity and trophic structure of the macrobenthic population of the Adour Estuary (South-West, France). The benthic macrofauna diversity indicates that inner estuarine stations are moderately polluted whereas outer estuarine stations are less impacted. However, metals concentrations in both sediment and benthic biomass do not change drastically between stations. Moreover, the bioaccumulation has been determined in relation to the feeding guild of benthic organisms. The results demonstrate that higher bioaccumulation is generally observed for deposit feeders directly impacted by sediment contamination compared to suspensive feeders and predators. Biomagnification along the trophic levels was highlighted for MMHg but no significant trend was observed for the other metallic compounds.     

Suspended particulate matter determines physical speciation of Fe,Mn, and trace metals in surface waters of Loire watershed

This study investigates the spatiotemporal variability of major and trace elements, dissolved organic carbon (DOC), total dissolved solids (TDS), and suspended particulate matter (SPM) in surface waters of several hydrosystems of the Loire River watershed in France. In particular, this study aims to delineate the impact of the abovementioned water physicochemical parameters on natural iron and manganese physical speciation (homoaggregation/heteroaggregation) among fine colloidal and dissolved (<?10 nm), colloidal (10–450 nm) and particulate (>?450 nm) phases in Loire River watershed. Results show that the chemistry of the Loire River watershed is controlled by two end members: magmatic and metamorphic petrographic context on the upper part of the watershed; and sedimentary rocks for the middle and low part of the Loire. The percentage of particulate Fe and Mn increased downstream concurrent with the increase in SPM and major cations concentration, whereas the percentage of colloidal Fe and Mn decreased downstream. Transmission electron microscopy analyses of the colloidal and particulate fractions (from the non-filtered water sample) revealed that heteroaggregation of Fe and Mn rich natural nanoparticles and natural organic matter to the particulate phase is the dominant mechanism. The heteroaggregation controls the partitioning of Fe and Mn in the different fractions, potentially due to the increase in the ionic strength, and divalent cations concentration downstream, and SPM concentration. These findings imply that SPM concentration plays an important role in controlling the fate and behavior of Fe and Mn in various sized fractions.

Physical speciation by heteroaggregation of (Fe-Mn) compounds: high [SPM]?→?[Fe-Mn] particulate faction; low {SPM]?→?[Fe-Mn] colloid-dissolved fraction.

     

Protein kinase C and ion transport in the posterior gills of the Chinese crabEriocheir sinensis

The possible involvement of protein kinase C in control of ion transport was investigated on a preparation of isolated, perfused posterior gills of the Chinese crabsEriocheir sinensis (collected in 1989 from lakes near Emden, northern Germany) acclimated to fresh water. 1-oleyl-2-acetyl-sn-glycerol (OAG) and phorbol 12-myristate 13-acetate (PMA), two activators of protein kinase C, when added to the perfusion saline, induced depolarisation of the transepithelial potential difference (PD) and an increase in transepithelial Na⁺ influx. The observed increase was proportional to OAG concentration up to 250µM, with a 2.5× accelerated Na⁺ influx. OAG and PMA remained without effect on Cl^– fluxes. The observed effects were in agreement with an activation, via protein kinase C, of the Na⁺/K⁺ ATPase located on the serosal side of the epithelium.     

Plant Bioavailability of “natural” and “model” Humic acid‐bound [14c] Atrazine residues

The release of bound [14C] atrazine residues and their uptake by maize plants was investigated.

“Natural”; humic acids, extracted from a brown soil, and “model”; humic acids, prepared from catechol, both containing bound [14C] atrazine residues were incubated with plants in soil. After 21 days, the maize plants contained 0.7% (plants grown in soil mixed with “natural”; humic acids) to 1.7% (plants grown in soil mixed with “model”; humic acids) of the radioactivity originally introduced.

The roots contained 55 to 70% of the [14C] residues whereas the remainder was present in the shoots. A significant amount of the total [14C] residues (29 to 53%) became again bound in plant tissues, whereas the, majority of extractable [14C] residues was present in the form of conjugates.

The behaviour of “model”; humic acid‐bound residues was comparable to that of “natural”; humic acid‐bound residues or soil‐bound residues.