The potential of the diverse chemistries present in natural products (NP) for biotechnology and medicine remains untapped because NP databases are not searchable with raw data and the NP community has no way to share data other than in published papers. Although mass spectrometry techniques are well-suited to high-throughput characterization of natural products, there is a pressing need for an infrastructure to enable sharing and curation of data. We present Global Natural Products Social molecular networking (GNPS, http://gnps.ucsd.edu), an open-access knowledge base for community wide organization and sharing of raw, processed or identified tandem mass (MS/MS) spectrometry data. In GNPS crowdsourced curation of freely available community-wide reference MS libraries will underpin improved annotations. Data-driven social-networking should facilitate identification of spectra and foster collaborations. We also introduce the concept of ‘living data’ through continuous reanalysis of deposited data.

For many decades, Escherichia coli was the main model organism for the study of bacterial membrane lipids. The results obtained served as a blueprint for membrane lipid biochemistry, but it is clear now that there is no such thing as a typical bacterial membrane lipid composition. Different bacterial species display different membrane compositions and even the membrane composition of cells belonging to a single species is not constant, but depends on the environmental conditions to which the cells are exposed. Bacterial membranes present a large diversity of amphiphilic lipids, including the common phospholipids phosphatidylglycerol, phosphatidylethanolamine and cardiolipin, the less frequent phospholipids phosphatidylcholine, and phosphatidylinositol and a variety of other membrane lipids, such as for example ornithine lipids, glycolipids, sphingolipids or hopanoids among others. In this review, we give an overview about the membrane lipid structures known in bacteria, the different metabolic pathways involved in their formation, and the distribution of membrane lipids and metabolic pathways across taxonomical groups.

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AtAMT2 is an ammonium transporter that is only distantly related to the five members of the AtAMT1 family of high-affinity ammonium transporters in Arabidopsis. The short-lived radioactive ion 13 NH 4 ϩ was used to show that AtAMT2, expressed in yeast (Saccharomyces cerevisiae), is a high-affinity transporter with a K m for ammonium of about 20 m. Changes in external pH between 5.0 and 7.5 had little effect on the K m for ammonium, indicating that NH 4 ϩ , not NH 3 , is the substrate for AtAMT2. The AtAMT2 gene was expressed in all organs of Arabidopsis and was subject to nitrogen (N) regulation, at least in roots where expression was partially repressed by high concentrations of ammonium nitrate and derepressed in the absence of external N. Although expression of AtAMT2 in shoots responded little to changes in root N status, transcript levels in leaves declined under high CO 2 conditions. Transient expression of an AtAMT2-green fluorescent protein fusion protein in Arabidopsis leaf epidermal cells indicated a plasma membrane location for the AtAMT2 protein.Thus, AtAMT2 is likely to play a significant role in moving ammonium between the apoplast and symplast of cells throughout the plant. However, a dramatic reduction in the level of AtAMT2 transcript brought about by dsRNA interference with gene expression had no obvious effect on plant growth or development, under the conditions tested.Ammonium and nitrate are thought to be the primary sources of nitrogen (N) for most plants growing in agricultural soils. Acquisition of these inorganic nutrients from the soil solution involves a variety of different transporters, which transport the ions from the apoplast of root epidermal and cortical cells into the symplast. Although ammonium concentrations are often 10 to 1,000 times lower than those of nitrate in well-aerated soil, ammonium nutrition plays an essential role in waterlogged and acid soils (Marschner, 1995). Furthermore, ammonium seems to be a preferred source of N and is taken up more rapidly than nitrate when both ions are presented simultaneously to plants (Gazzarrini et al., 1999).Physiological studies of ammonium transport into roots have revealed biphasic kinetics in several species (Fried et al., 1965;Vale et al., 1988;Wang et al., 1993). The so-called high-affinity ammonium transport system is predominant at low (submillimolar) concentrations of substrate (NH 4 ϩ ) and exhibits saturation kinetics. A second component of ammonium uptake is the low-affinity transport system, which becomes significant at higher external ammonium concentrations (above 1 mm) and exhibits nonsaturation kinetics (Wang et al., 1993;Kronzucker et al., 1996). Although the molecular basis of low-affinity transport system activity remains unknown, there is growing evidence that members of the AMT1 family of transporters are responsible for high-affinity ammonium transport system activity in plants. The first AMT1 gene to be discovered in plants was AtAMT1;1 from Arabidopsis, which was cloned by complementation of a yeast (Sacchar...

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