Factors Influencing the Diversity of Iron Uptake Systems in Aquatic Microorganisms

Iron (Fe) is an essential micronutrient for many processes in all living cells. Dissolved Fe (dFe) concentrations in the ocean are of the order of a few nM, and Fe is often a factor limiting primary production. Bioavailability of Fe in aquatic environments is believed to be primarily controlled through chelation by Fe-binding ligands. Marine microbes have evolved different mechanisms to cope with the scarcity of bioavailable dFe. Gradients in dFe concentrations and diversity of the Fe-ligand pool from coastal to open ocean waters have presumably imposed selection pressures that should be reflected in the genomes of microbial communities inhabiting the pelagic realm. We applied a hidden Markov model (HMM)-based search for proteins related to cellular iron metabolism, and in particular those involved in Fe uptake mechanisms in 164 microbial genomes belonging to diverse taxa and occupying different aquatic niches. A multivariate statistical approach demonstrated that in phototrophic organisms, there is a clear influence of the ecological niche on the diversity of Fe uptake systems. Extending the analyses to the metagenome database from the Global Ocean Sampling expedition, we demonstrated that the Fe uptake and homeostasis mechanisms differed significantly across marine niches defined by temperatures and dFe concentrations, and that this difference was linked to the distribution of microbial taxa in these niches. Using the dN/dS ratios (which signify the rate of non-synonymous mutations) of the nucleotide sequences, we identified that genes encoding for TonB, Ferritin, Ferric reductase, IdiA, ZupT, and Fe(2+) transport proteins FeoA and FeoB were evolving at a faster rate (positive selection pressure) while genes encoding ferrisiderophore, heme and Vitamin B12 uptake systems, siderophore biosynthesis, and IsiA and IsiB were under purifying selection pressure (evolving slowly)

Facets of diazotrophy in the oxygen minimum zone waters off Peru

Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4+), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2− and PO43− are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the futu

Trends in Fragmentation of Production: A Comparative Study of Asia and Latin America

AbstractDuring the last decade dramatic changes have taken place in the direction and pattern of trade of the emerging economies. Notable amongst them is the thriving trade in rsquo;fragmentation’ also called trade in Parts, Components and Accessories (PCA) wherein the production process is split into two or more steps. This growth in fragmentation trade involves relocating production stages to low cost countries where labour is abundant. In this paper, we examine and compare the trends in PCA exports of 12 emerging economies (9 from Asia and 3 from Latin America) for a period from 1994 to 2009. Empirical evidence suggests that considerable churning has taken place in Asia in exports of PCA as compared to countries in Latin America. For instance, Singapore occupied a leading position in 1994, but vacated it in 2002 which was occupied by Philippines. Further, we examine the share of Electronics and Automotive parts in total PCA exports and find that exports of Electronic parts account for a dominant share of PCA exports in Asia, but that of Automotive parts are a small fraction of the total PCA exports. But on the other hand, although exports of PCA are a small percentage of total exports in the Latin American countries, the production networks in automotive parts are more advanced compared to Asia. We use the Lafay index of specialization to study the changing comparative advantage of countries over time. The Logistic Performance Index and the Foreign Direct Investment inflows can to some extent explain the booming PCA trade. It is against this backdrop that we argue that there is need for a paradigm shift in the trade policies formulated and implemented by the governments. Policies must ensure productivity gains, up gradation of the manufacturing sector, expansion of domestic demand, participation of all segments of the population in income generation and so on

Anticorrosive properties of Eucalyptus (Nilgiris) leaves extract on 2S grade aluminium in acid solutions

The study is on the application of Eucalyptus leaves extract (ELE) as anticorrosive properties for aluminium alloy in 0.5 M HCl by using potentiodynamic polarization (PDP), gravimetric weight loss, and Electrochemical impedance spectroscopic (EIS) methods. The corrosion inhibition characteristics of ELE on aluminium in HCl solution have been examined. This investigation showed the finest inhibition efficiencies of 95.0%, 92.0% and 89.3% that were obtained from weight loss, PDP and EIS at concentration of 0.5% ELE at 303 K respectively. As per Langmuir adsorption isotherm models, an extract of Eucalyptus leaves was adsorbed on the metal surface. The effect of the temperature on the corrosion behaviour with adding of the best concentration of ELE was studied in the temperature range 313–333 K. It was found that inhibition efficiency is independent of temperature. The negative Gibb's free energy and activation parameters of the ELE were recorded and the results indicated that the adsorption rates were spontaneous. The results obtained from PDP and EIS shows that the corrosion inhibition procedure is charge transfer controlled, and the ELE works as a mixed-type inhibitor. The findings of SEM (Scanning electron microscopy) and AFM (Atomic forcemicroscopy) studies support the adsorption inhibition mechanism. The results of all the experiments conduct are consistent. The functional groups of the ELE were identified using Fourier transform infrared (FTIR) spectroscopy

Nitrogen fixation and nitrogen gene abundance of METEOR cruises M77/3 and M77/4

Nitrogen fixation, the biological reduction of dinitrogen gas (N2) to ammonium (NH4+), is quantitatively the most important external source of new nitrogen (N) to the open ocean. Classically, the ecological niche of oceanic N2 fixers (diazotrophs) is ascribed to tropical oligotrophic surface waters, often depleted in fixed N, with a diazotrophic community dominated by cyanobacteria. Although this applies for large areas of the ocean, biogeochemical models and phylogenetic studies suggest that the oceanic diazotrophic niche may be much broader than previously considered, resulting in major implications for the global N-budget. Here, we report on the composition, distribution and abundance of nifH, the functional gene marker for N2 fixation. Our results show the presence of eight clades of diazotrophs in the oxygen minimum zone (OMZ) off Peru. Although proteobacterial clades dominated overall, two clusters affiliated to spirochaeta and archaea were identified. N2 fixation was detected within OMZ waters and was stimulated by the addition of organic carbon sources supporting the view that non-phototrophic diazotrophs were actively fixing dinitrogen. The observed co-occurrence of key functional genes for N2 fixation, nitrification, anammox and denitrification suggests that a close spatial coupling of N-input and N-loss processes exists in the OMZ off Peru. The wide distribution of diazotrophs throughout the water column adds to the emerging view that the habitat of marine diazotrophs can be extended to low oxygen/high nitrate areas. Furthermore, our statistical analysis suggests that NO2- and PO43- are the major factors affecting diazotrophic distribution throughout the OMZ. In view of the predicted increase in ocean deoxygenation resulting from global warming, our findings indicate that the importance of OMZs as niches for N2 fixation may increase in the futu