Plants, and all other living things, require nitrogen for growth; it is an essential component of nucleic acids and proteins. Although air is mostly nitrogen, this gaseous form is inaccessible to plants and must be fixed into ammonium to render it biologically relevant. Soil bacteria called rhizobia fix nitrogen, but to do this they must first take up residence inside the roots of legumes like pea, alfalfa, clover, and soybean.
Experimental Evolution of a Plant Pathogen into a Legume Symbiont:
Most leguminous plants can form a symbiosis with members of a group of soil bacteria known as rhizobia. On the roots of their hosts, some rhizobia elicit the formation of specialized organs, called nodules, that they colonize intracellularly and within which they fix nitrogen to the benefit of the plant. Rhizobia do not form a homogenous taxon but are phylogenetically dispersed bacteria. How such diversity has emerged is a fascinating, but only partly documented, question. Although horizontal transfer of symbiotic plasmids or groups of genes has played a major role in the spreading of symbiosis, such gene transfer alone is usually unproductive because genetic or ecological barriers restrict evolution of symbiosis. Here, we experimentally evolved the usually phytopathogenic bacterium Ralstonia solanacearum, which was carrying a rhizobial symbiotic plasmid into legume-nodulating and -infecting symbionts. From resequencing the bacterial genomes, we showed that inactivation of a single regulatory gene allowed the transition from pathogenesis to legume symbiosis. Our findings indicate that following the initial transfer of symbiotic genes, subsequent genome adaptation under selection in the plant has been crucial for the evolution and diversification of rhizobia.
The Global Health System: Strengthening National Health Systems as the Next Step for Global Progress:
Three circumstances make the present moment unique for global health. First, health has been increasingly recognized as a key element of sustainable economic development [1], global security, effective governance, and human rights promotion [2]. Second, due to the growing perceived importance of health, unprecedented--albeit still insufficient--sums of funds are flowing into this sector [3]. Third, there is a burst of new initiatives coming forth to strengthen national health systems as the core of the global health system and a fundamental strategy to achieve the health-related Millennium Development Goals.
In order to realize the opportunities offered by the conjunction of these unique circumstances, it is essential to have a clear conception of national health systems that may guide further progress in global health. To that effect, the first part of this Policy Forum examines some common misconceptions about health systems. Part two explains a framework to better understand this complex field. Finally, I offer a list of suggestions on how to improve national health system performance and what role global actors can play.
The primary goal of public health, the branch of medicine concerned with the health of communities, is to improve lives by preventing disease. Public-health groups do this by assessing and monitoring the health of communities, by ensuring that populations have access to appropriate and cost-effective health care, and by helping to formulate public policies that safeguard human health. Until recently, most of the world's major public-health concerns related to infectious diseases. Nowadays, however, many major public-health concerns are linked to the goods made and marketed by large corporations such as fast food, alcohol, tobacco, and chemicals. In Europe, these corporations are regulated by policies drawn up both by member states and by the European Commission, the executive organ of the European Union (EU; an economic and political partnership among 27 democratic European countries). Thus, for example, the tobacco industry, which is widely recognized as a driver of the smoking epidemic, is regulated by Europe-wide tobacco control policies and member state level policies.
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