In Silico Insights into the Symbiotic Nitrogen Fixation in Sinorhizobium meliloti via Metabolic Reconstruction

BACKGROUND: Sinorhizobium meliloti is a soil bacterium, known for its capability to establish symbiotic nitrogen fixation (SNF) with leguminous plants such as alfalfa. S. meliloti 1021 is the most extensively studied strain to understand the mechanism of SNF and further to study the legume-microbe interaction. In order to provide insight into the metabolic characteristics underlying the SNF mechanism of S. meliloti 1021, there is an increasing demand to reconstruct a metabolic network for the stage of SNF in S. meliloti 1021. RESULTS: Through an iterative reconstruction process, a metabolic network during the stage of SNF in S. meliloti 1021 was presented, named as iHZ565, which accounts for 565 genes, 503 internal reactions, and 522 metabolites. Subjected to a novelly defined objective function, the in silico predicted flux distribution was highly consistent with the in vivo evidences reported previously, which proves the robustness of the model. Based on the model, refinement of genome annotation of S. meliloti 1021 was performed and 15 genes were re-annotated properly. There were 19.8% (112) of the 565 metabolic genes included in iHZ565 predicted to be essential for efficient SNF in bacteroids under the in silico microaerobic and nutrient sharing condition. CONCLUSIONS: As the first metabolic network during the stage of SNF in S. meliloti 1021, the manually curated model iHZ565 provides an overview of the major metabolic properties of the SNF bioprocess in S. meliloti 1021. The predicted SNF-required essential genes will facilitate understanding of the key functions in SNF and help identify key genes and design experiments for further validation. The model iHZ565 can be used as a knowledge-based framework for better understanding the symbiotic relationship between rhizobia and legumes, ultimately, uncovering the mechanism of nitrogen fixation in bacteroids and providing new strategies to efficiently improve biological nitrogen fixation

A diverse assemblage of Anacardiaceae from Oligocene sediments, Tepexi de Rodríguez, Puebla, Mexico

Among the plants collected from the Pie de Vaca Formation of the Oligocene, of Tepexi de Rodríguez, Puebla, Mexico are five plants of Anacardiaceae, Haplorhus medranoensis, Rhus toxicodendron, Rhus sp., Comocladia intermedia, and Pistacia marquezu represented by their leaves and/or leaflets. The past and present diversity and geographic distribution of one of these genera, Rhus, demonstrate its capability to adapt and diversify in a wide variety of environments. Leaf architecture characters of this taxon overlap with those of other genera in the family, suggesting a high degree of phenotypic plasticity. The presence in the Pie de Vaca Formation of a type of Pistacia with leaf architecture characters similar to those of Asian plants further supports a long history of exchange between low-latitude North America and Asia. Links between low-latitude North and South America and the Caribbean are suggested by the presence of Comocladia and Haplorhus. Whereas Comocladia highlights the long history of regional endemics in the area, Haplorhus, today an endemic monotypic genus of Peru, suggests exchange mechanisms between North and South America. The morphologic characters of these taxa, and those of Pseudosmodingium (Anacardiaceae), some Rosaceae, Leguminosae, and Berberidaceae, suggest that the Pie de Vaca community was established and evolved in harsh environmental conditions. The Pie de Vaca flora thus provides significant new insights into the biogeographic relationships of the low latitude vegetation of North America

Leaves of salicaceae (Salix and Populus) from Oligocene sediments near Tepexi de Rodríguez, Puebla, Mexico

Eleven new salicaceous taxa based on fossil leaves, seven Salix and four Populus species, are described from the Oligocene Los Ahuehuetes locality Pie de Vaca Formation, near Tepexi de Rodríguez in Puebla, Mexico. They are characterized by the presence of typical salicoid teeth, camptodromous secondary venation, and elliptic or lanceolate shape. Morphological differences between these new fossil plants and those reported previously from the United States and elsewhere indicate that diversification among these taxa occurred early during their differentiation. Furthermore, the limited morphological similarities of the fossil and extant plants growing naturally in Mexico also indicate a high rate of evolution. Documenting the expansion of high-latitude North American taxa into lower latitudes at the time of deposition of the Pie de Vaca Formation confirms that at least some of the typical boreal taxa were part of dry tropical communities in low-latitude North America and underscores the need to reevaluate the origin of this southern vegetation

Leaves of Berberidaceae (Berberis and Mahonia) from Oligocene sediments, near Tepexi de Rodríguez, Puebla.

From the Oligocene Los Ahuehuetes locality, near Tepexi de Rodríguez, Puebla, Mexico, five new plant species are described based on their leaf architecture. The presence of brochidodromous or acrodromous venation, and secondary veins forming angular (versus rounded) arcs, are well defined characters in the fossil material that relate it to Berberidaceae. Comparison with the leaves and leaflets of extant and fossil plants allow the recognition of one Mahonia and four Berberis is new species. The lack of detailed information on leaf architecture in Berberidaceae limits the evaluation of the taxonomic relationships that can be suggested between fossil and extant plants. However, from a biogeographic point of view the presence of these new fossil plants supports the hypothesis of a North American origin of the Orientalis Groups of Mahonia, to which a lineage of Berberis may be added. Furthermore, two of the new species suggest the dispersal, some time during the Tertiary, of a lineage that today forms the Australis Group of Berberis from low latitude North America to South America. The movement of the Chortis Block is proposed as an alternative to explain the dispersal of a growing list of plants from north to south in the Americas. Only through future geological and palaeobotanical work call this hypothesis be corroborated. (C) 2000 Elsevier Science B.V. All rights reserved

Reconstruction of the leaves of two new species of Pseudosmodingium (anacardiaceae) from Oligocene strata of Puebla, Mexico

they are symmetrical to slightly asymmetrical, with acute to attenuate apex, acute to cuneate base, and entire to serrate margin. Venation is simple pinnate craspedodromous, with secondary veins slightly curved near their bas

The South American Physical Activity and Sedentary Behavior Network (SAPASEN)

The present article describes the South American Physical Activity and Sedentary Behavior Network, which was designed to provide ongoing transnational empirical evidence about physical activity and sedentary behavior in South America. The first goal of this initiative was to form a representative body of researchers and policy makers from all South American countries (Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela) to establish priorities and targets for the short, medium and long term. Examples are given of connecting physical activity and sedentary data from existing surveys in several of the partner countries. The main objective of the South American Physical Activity and Sedentary Behavior Network will be to impact policies on physical activity and sedentary behavior in South America according to the singularities of each country or region. By encouraging an inclusive and collaborative effort, we expect that the South American Physical Activity and Sedentary Behavior Network will support the connection between researchers from South America as well as provide a better comprehension of the epidemiology of physical activity and sedentary behavior regionally