The nitrogen-fixing organisms. Free-living heterotrophic nitrogen-fixing bacteria. Nitrogen-fixing bacteria in the rhizosphere. Nitrogen fixation in the phyllosphere. Photosynthetic bacteria. Blue-gree algae. Associations with blue-green algae. Root-nodule symbioses with rhizobium. Root-nodulesymbioses withactinomycete-like organisms. Development of root-nodule symbioses. Root-nodule morphogenesis. Formation and function of bacteroids. The endophytes of the root nodules in nonleguminous plants. Leghemoglobin. Environmental effects on nodulation and symbiotic nitrogen fixation. Putative nitrogen fixation in other symbioses. The nitrogen-fixing system. The enzyme system. Genetics of N2-fixing organisms.

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 book provides an introductory-level survey of biological nitrogen fixation, covering the role of the process in the global nitrogen cycle as well as its biochemistry, physiology, genetics, ecology, general biology and prospects for its future exploitation.

Our knowledge of the biochemistry and biophysics of dinitrogen fixa tion has developed rapidly in the 15 years since the first N2-fixing enzyme system was successfully extracted from a bacterium. This peri od has produced a literature that now describes the N2 fixation reac tion and the nitrogenase enzyme itself in sophisticated terms, though a detailed reaction mechanism at the chemical level has not yet emerged. It is the purpose of the present monograph to present an in-depth re view, analysis, and integration of this research as is possible with a non-contributed publication and to relate this work to considera tions of N2 fixation that reach beyond the confines of the biochem ist's laboratory. The first section is directed as much toward the general science read er as toward the specialist. It covers the agricultural origins of man's interest in N2 fixation and also pertinent areas of taxonomy, physiology, and evolution. Ecological aspects of the subject include a comprehensive evaluation of the nitrogen cycle leading to a sub stantially greater estimate of the rate of global N2 fixation than previous ones. The treatment is of a survey fashion, in part to pro vide a general over-view of N2 fixation and in part to provide context for the biochemistry and biophysics that follow in the second section.

Biological nitrogen fixation has essential role in N cycle in global ecosystem. Several types of nitrogen fixing bacteria are recognized: the free-living bacteria in soil or water; symbiotic bacteria making root nodules in legumes or non-legumes; associative nitrogen fixing bacteria that resides outside the plant roots and provides fixed nitrogen to the plants; endophytic nitrogen fixing bacteria living in the roots, stems and leaves of plants. In this book there are 11 chapters related to biological nitrogen fixation, regulation of legume-rhizobium symbiosis, and agriculture and ecology of biological nitrogen fixation, including new models for autoregulation of nodulation in legumes, endophytic nitrogen fixation in sugarcane or forest trees, etc. Hopefully, this book will contribute to biological, ecological, and agricultural sciences.

Nitrogen availability is one of the most critical factors that limits plant productivity. The largest reservoir of nitrogen is the atmosphere, but this gaseous molecular nitrogen only becomes available to plants through the biological nitrogen fixation process, which only prokaryotic cells have developed. The discovery that microbes were providing fixed nitrogen to legumes and the isolation of the first nitrogen-fixing bacteria occured at the end the 19th Century, in Louis Pasteur's time. We are now building on more than 100 years of research in this field and looking towards the 21st Century. The International Nitrogen Fixation Congress series Started more than 20 years ago. The format of this Congress is designed to gather scientists from very diverse origins, backgrounds, interests and scientific approaches and is a forum where fundamental knowledge is discussed alongside applied research. This confluence of perspectives is, we believe, extremely beneficial in raising new ideas, questions and concepts.