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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.
The cultivation of diazotrophic microorganisms. Measurement of nitrogen fixation by direct means. Measurement of nitrogen fixation by indirect means. Methods for legumes in glasshouses and controlled environment cabinets. Non-legumes nodule systems. Methods for studying nitrogenase. Methods for studying enzymes involved in metabolism related to nitrogenase. Preparation and experimental use of leghaemoglobin. Methods for identifying strains of diazotrophs. Genetic studies with diazotrophs. Experiments with crop and pasture legumes: principles and practice. Production and quality control of legume inoculants. Forage grasses and grain crops. Nitrogen fixation in natural plant communities and soils. Sytems involving blue-green algae (cyanobacteria).
The symbiotic tree legume, mesquite, forms two lateral root systems when able to access surface and ground water and both systems have associated nitrogen fixing bacteria. Contribution to ecosystem productivity requires mesquite's renewal of symbiosis under extreme, changing conditions. Rhizobial and bradyrhizobial populations associated with surface and deep rooting systems of a mature Sonoran Desert mesquite woodland were isolated by four to six meters of dry soil for centuries. To determine whether differences in microsymbiont physiology were paralleled genetically, we assessed their host ranges, symbiotic gene region polymorphisms, and plasmid patterns. Restriction enzyme-digested genomic DNA of isolates from the two mesquite root zones showed nif, nod, and ndv-hybridization patterns corresponding to their source root zone. The patterns indicated that all isolates of either genus, Rhizobium and Bradyrhizobium, were related, but different, with soil depth. Plasmid profile analyses revealed differences, most prominently, in lesser deep bradyrhizobial plasmid DNA content. Identical host ranges were consistent with relatedness among isolates. We concluded these were clonal populations that varied under alternating symbiotic and free-living selections within soil compartments. Towards understanding host-specific nodulation of the unimproved woody legume, mesquite, we used marker rescue strategies to isolate DNA clones of mesquite-symbiont nodulation regions. Mesquite selected cloned rhizobial DNA from the same genomic region by extending the nodulation range of broad host Rhizobium sp. strain NGR234 or restoring nodulation to Nod-Rhizobium sp. strain HW27c. In those clones, a nodD locus and adjacent nod box sequence were organized similarly to common nodulation regions of other micosymbionts. Whether containing nodD, or not, subcloned regions carried by non-nodulating strains did not confer mesquite nodulation, In contrast, cloned bradyrhizobial genomic DNA lacking nodD similarity extended the host range of Rhizobium sp. strain NGR234 without restoring nodulation to Rhizobium sp. strain HW27c. We found genetic parallels to physiological variation among populations that extends knowledge of how selection for the symbiotic life cycle interacts with longterm microbial survival under extreme conditions. Molecular analysis of the mesquite-bacterial association gives insight to the nodulation process, well-characterized for temperate crops, in an unimproved, tropical tree symbiosis.
Rhizobia are bacteria which inhabit the roots of plants in the pea family and "fix" atmospheric nitrogen for plant growth. They are thus of enormous economic importance internationally and the subject of intense research interest. Handbook for Rhizobia is a monumental book of practical methods for working with these bacteria and their plant hosts. Topics include the general microbiological properties of rhizobia and their identification, their potential as symbionts, methods for inoculating rhizobia onto plants, and molecular genetics methods for Rhizobium in the laboratory. The book will be invaluable to Rhizobium scientists, soil microbiologists, field and laboratory researchers at agricultural research centers, agronomists, and crop scientists.
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.
I. Manipulation of Rhizobia; II. Field and greenhouse assessment of N2 fixation.
This book covers broad areas in the conservation of microorganisms. It addresses the short, medium and long-term preservation of agriculturally important microorganisms, as well as culture collections and their roles. The respective chapters address topics such as conventional approaches to bacterial, fungal and algal preservation, as well as methods and strategies for preserving recalcitrant microorganisms. Readers will also find the latest insights into the preservation of vesicular-arbuscular (VA) fungi and ecology, diversity and conservation of endophytes, and entamopathogenic fungi. Microbes of animal and dairy origin, their preservation and biosafety issues are also explored. Microorganisms are the silent and unseen majority of life on Earth, and are characterized by a high degree of genetic and metabolic diversity. It is well documented that no branch of science or society is unaffected by microbial interventions. Researchers have documented microorganisms from such extreme and unique environments as deserts and hydrothermal vents, and with specific traits that are currently being exploited in agriculture, industry, medicine and biotechnological applications. Such great potential can only be found in microorganisms. The aim of this book – the first entirely devoted to the conservation of microorganisms, and to regulatory mechanisms for access and benefits sharing as per Biological Diversity (BD) Act 2002 – is to promote awareness of our world’s microbial wealth, and to introduce readers to strategies and methodologies for the conservation of microorganisms, which could ultimately save human life on Earth.
General information on the symbiotic nitrogen fixation. Isolation, identification and counting of rhizobia. Production of an inoculant and inoculation of legumes. Experiments.