Genetics as a tool to understand structure and function; Vector technology of relevance to nitrogen fixation research; The Azolla-Anabaena symbiosis; The genetics of the Frankia-actinorhizal symbiosis; Legume nodule biochemistry and function; The Rhizobium/bradyrhizobium-legume symbiosis; Nitrate inhibition of nodulation in legumes; Nodulin function and nodulin gene regulation in root nodule development; The Parasponia-bradyrhizobium symbiosis.

Phylogenetic classification of nitrogen-fixing organisms. Physiology of nitrogen fixation in free-living heterotrophs. Nitrogen fixation by photosynthetic bacteria. Nitrogen fixation in cyanobacteria. Nitrogen fixation by methanogenic bacteria. Associative nitrogen-fixing bacteria. Actinorhizal symbioses. Ecology of bradyrhizobium and rhizobium. The rhizobium infection process. Physiology of nitrogen-fixing legume nodules: compartments, and functions. Hydrogen cycling in symbiotic bacteria. Evolution of nitrogen-fixing symbioses. The rhizobium symbiosis of the nonlegume parasponia. Genetic analysis of rhizobium nodulation. Nodulins in root nodule development. Plant genetics of symbiotic nitrogen fixation. Molecular genetics of bradyrhizobium symbioses. The enzymology of molybdenum-dependent nitrogen fixation. Alternative nitrogen fixation systems. Biochemical genetics of nitrogenase. Regulation of nitrogen fixation genes in free-living and symbiotic bacteria. Isolated iron-molybdenum cofactor of nitrogenase.

This volume is a wide-ranging critical evaluation by international experts of the state of knowledge in the whole field of biological nitrogen fixation. It includes coverage of the chemistry of N2 reduction, the biochemistry and molecular biology of the molybdenum and vanadium nitrogenases. There is review of the whole range of organisms fixing N2, including the free-living and symbiotic organisms (bacteria, cyanobacteria, actinomycetes). Detailed consideration is given to the ecology and agricultural use of the root nodule bacteria, the molecular biology and biochemistry of nodule formation and fuction. The practicability of extending symbiotic N2-fixation to other systems or to greater efficiency is examined.

During the past three decades there has been a large amount of research on biological nitrogen fixation, in part stimulated by increasing world prices of nitrogen-containing fertilizers and environmental concerns. In the last several years, research on plant--microbe interactions, and symbiotic and asymbiotic nitrogen fixation has become truly interdisciplinary in nature, stimulated to some degree by the use of modern genetic techniques. These methodologies have allowed us to make detailed analyses of plant and bacterial genes involved in symbiotic processes and to follow the growth and persistence of the root-nodule bacteria and free-living nitrogen-fixing bacteria in soils. Through the efforts of a large number of researchers we now have a better understanding of the ecology of rhizobia, environmental parameters affecting the infection and nodulation process, the nature of specificity, the biochemistry of host plants and microsymbionts, and chemical signalling between symbiotic partners. This volume gives a summary of current research efforts and knowledge in the field of biological nitrogen fixation. Since the research field is diverse in nature, this book presents a collection of papers in the major research area of physiology and metabolism, genetics, evolution, taxonomy, ecology, and international programs.

This book provides in-depth reviews of the role of Rhizobium in agriculture and its biotechnological applications. Individual chapters explore topics such as: the occurrence and distribution of Rhizobium; phenotypic and molecular characteristics of Rhizobium; impact of Rhizobium on other microbial communities in the rhizosphere; N2-fixation ability of Rhizobium; Rhizobium and biotic stress; Rhizobium-mediated restoration of an ecosystem; in silico analysis of the rhizobia pool; further biotechnological perspectives of Rhizobium.