Nitrogen is generally considered one of the major limiting nutrients in plant growth. The biological process responsible for reduction of molecular nitrogen into ammonia is referred to as nitrogen fixation. A wide diversity of nitrogen-fixing bacterial species belonging to most phyla of the Bacteria domain have the capacity to colonize the rhizosphere and to interact with plants. Leguminous and actinorhizal plants can obtain their nitrogen by association with rhizobia or Frankia via differentiation on their respective host plants of a specialized organ, the root nodule. Other symbiotic associations involve heterocystous cyanobacteria, while increasing numbers of nitrogen-fixing species have been identified as colonizing the root surface and, in some cases, the root interior of a variety of cereal crops and pasture grasses. Basic and advanced aspects of these associations are covered in this review.

There is a great demand for high-protein materials for livestock feed in Europe and European agriculture has a deficit of about 70% high protein materials of which 87% is met by imported soybean and soy meal. This reflects the fact that grain legumes are currently under represented in European agriculture and produced on only 1.5 % of the arable land in Europe compared with 14.5% on a worldwide basis. Several grain legumes have the potential to replace at least some of the soya currently used in the diets of monogastric animals, ruminants and fish. There are also opportunities for greater use of legumes in new foods. Here we review the contribution of ecosystem services by grain legumes in European agriculture starting with provisioning services in terms of food and feed and moving on to the contribution they make to both regulating and supporting services which are in part due to the diversity which these crops bring to cropping systems. We explore the need to understand grain legume production on the time scale of a rotation rather than a cropping season in order to value and manage the agronomic challenges of weed, pests and diseases alongside the maintenance or improvement of soil structure, soil organic matter and nutrient cycling. A review of policy interventions to support grain legumes reveals that until very recently these have failed to make a difference in Europe. We contrast the European picture with the interventions that have allowed the development of grain legume production in both Canada and Australia. Whether farmers choose to grow more legumes will depend on market opportunities, the development of supply chains and policy support as well as technical improvements of grain legume production such as breeding of new varieties and management development to improve yield stability. However, to really increase the production of grain legumes in Europe the issues are far more wide reaching than agronomy or subsidy and require a fundamental rethinking of value chains to move grain legumes from being niche products to mainstream commodities.

We report here the results of phylogenetic analysis of archaeal 16S rRNA gene sequences amplified by PCR with Archaea-specific primers with mixed-population DNA extracted directly from forest soil used as a template. Nucleotide signature and phylogenetic analyses show that the sequences obtained belong to the domain Archaea and form a new cluster. Its phylogenetic position suggests that sequences are from a previously undescribed terrestrial group within the kingdom Crenarchaeota.

Previous studies have demonstrated that cellular fatty acid analysis is a useful tool for identifying unknown strains of rhizobia and establishing taxonomic relationships between the species. In this study, the fatty acid profiles of over 600 strains belonging to the genera Agrobacterium, Bradyrhizobium, Mesorhizobium , Rhizobium and Sinorhizobium were evaluated using the gaschromatography-based Sherlock Microbial Identification System (MIS). Data collected with the MIS showed that the three phylogenetically defined biovars of the genus Agrobacterium formed discrete clusters, whilst species belonging to the genus Mesorhizobium formed three subclusters which were easily distinguished. These three subclusters contained Mesorhizobium ciceri and Mesorhizobium mediterraneum , Mesorhizobium tianshanense fatty acid group I and Mesorhizobium plurifarium, and Mesorhizobium huakuii and

Traditional Chinese medicinal plants are sources of biologically active compounds, providing raw material for pharmaceutical, cosmetic and fragrance industries. The endophytes of medicinal plants participate in biochemical pathways and produce analogous or novel bioactive compounds. Panxi plateau in South-west Sichuan in China with its unique geographical and climatological characteristics is a habitat of a great variety of medicinal plants. In this study, 560 endophytic actinomycetes were isolated from 26 medicinal plant species in Panxi plateau. 60 isolates were selected for 16S rDNA-RFLP analysis and 14 representative strains were chosen for 16S rDNA sequencing. According to the phylogenetic analysis, seven isolates were Streptomyces sp., while the remainder belonged to genera Micromonospora, Oerskovia, Nonomuraea, Promicromonospora and Rhodococcus. Antimicrobial activity analysis combined with the results of amplifying genes coding for polyketide synthetase (PKS-I, PKS-II) and nonribosomal peptide synthetase (NRPS) showed that endophytic actinomycetes isolated from medicinal plants in Panxi plateau had broad-spectrum antimicrobial activity and potential natural product diversity, which further proved that endophytic actinomycetes are valuable reservoirs of novel bioactive compounds.

Summary Biological nitrogen fixation in rhizobia occurs primarily in root or stem nodules and is induced by the bacteria present in legume plants. This symbiotic process has fascinated researchers for over a century, and the positive effects of legumes on soils and their food and feed value have been recognized for thousands of years. Symbiotic nitrogen fixation uses solar energy to reduce the inert N 2 gas to ammonia at normal temperature and pressure, and is thus today, especially, important for sustainable food production. Increased productivity through improved effectiveness of the process is seen as a major research and development goal. The interaction between rhizobia and their legume hosts has thus been dissected at agronomic, plant physiological, microbiological and molecular levels to produce ample information about processes involved, but identification of major bottlenecks regarding efficiency of nitrogen fixation has proven to be complex. We review processes and results that contributed to the current understanding of this fascinating system, with focus on effectiveness of nitrogen fixation in rhizobia.

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