IN INOCULANTS Nodulaid - 17th International Nitrogen Fixation ...

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17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Monday 28 November 2011 Concurrent Session 3 – Taxonomy & Evolution 1530 - 1650 Authors: Jelena Jalovaja 1 , Olga Tsoy 2,3 , Mikhail Gelfand 2,3 1Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, 141700, Russia 2 Institute for Information Transmission Problems RAS, Moscow, 127994,Russia 3 Lomonosov Moscow State University, Department of Bioengineering and Bioinformatics, Moscow, 119992, Russia Presentation Title: Comparative-genomic reconstruction of the NifA regulon evolution in alphaproteobacteria Presentation Time: 1610 - 1630 Nitrogen fixation is a complex redox process performed by a variety of bacteria. Since it requires a large amount of energy, and its main enzyme, nitrogenase, may be easily destroyed by oxygen, this process is tightly controlled at all levels, including the level of transcription. This study focuses on NifA, a major regulator of genes associated with nitrogen fixation. The NifA regulon has already been described for B.japonicum and R.etli [1, 2], but availability of complete genome sequences of other nitrogen fixing bacteria allows one to apply comparative genomics methods for accurate regulatory annotation. Analysis of 22 alpha-proteobacteria confirmed and further specified the NifA-binding motif TGT-N10-ACA. An evolutionary scenario of operon rearrangement and horizontal gene transfer was reconstructed. The conserved regulon core contains: � nifHDK, coding nitrogenase components, � iscNnifUS operon, coding nitrogenase FeS cluster assembly, � nifBfdxN coding Fe-Mo cofactor biosynthesis proteins, � fixABCX electron carrier Interestingly, NifA-RpoN sites were identified upstream of “broken” operon parts. The autoregulation of nifA in the Rhizobiales was confirmed, within operons fixABCX-nifA, fixR-nifA or ahpCD-nifA specific for individual taxa. New candidate regulon members are typically organism-specific and include molybdenum transporter genes, rpoN and nodulation genes. 1. Salazar E, Díaz-Mejía JJ, Moreno-Hagelsieb G, et al. Characterization of the NifA-RpoN Regulon in Rhizobium etli in Free Life and in Symbiosis with Phaseolus vulgaris. Applied and environmental microbiology. 2010; 76(13):4510-4520. 2. Hauser F, Pessi G, Friberg M, et al. Dissection of the Bradyrhizobium japonicum NifA+sigma54 regulon, and identification of a ferredoxin gene (fdxN) for symbiotic nitrogen fixation. Molecular genetics and genomics : MGG. 2007; 278(3):255-71. 32 2011
17 th International Congress on Nitrogen Fixation Fremantle, Western Australia 27 November – 1 December 2011 Session Details: Monday 28 November 2011 Concurrent Session 3 – Taxonomy & Evolution 1530 - 1650 Authors: Tadashi Yokoyama 1 , Chandra Prasad Risal 2 , Naoko Ohkama-Ohtsu 1 , Salem Djedidi 3 & Hitoshi Sekimoto 4 1 Institute of Agriculture, Tokyo Univ. of Agri. and Tech., Saiwai-cho 3-5-8, Fuchu, Tokyo 183-8509, Japan 2 Soil Management Directorate, Dept. of Agriculture, Hariharbhawan 552-0314, Nepal 3 Faculty of Agriculture, Tokyo Univ. of Agri. and Tech., Tokyo 183-8509, Japan 4 Faculty of Agriculture, Utsunomiya University, Utsunomiya 321-8505, Japan Presentation Title: Genetic diversity of native soybean and mungbean bradyrhizobia from different topographical regions along the southern slopes of the Himalayan Mountains in Nepal Presentation Time: 1630 - 1650 Soybean-nodulating bradyrhizobia are genetically diverse and are classified into different species. In this study, the genetic diversity of native soybean and mungbean bradyrhizobia isolated from different topographical regions along the southern slopes of the Himalayan Mountains in Nepal was explored. Soil samples were collected from three different topographical regions with contrasting climates. Local Glycine max cv. Cobb and Vigna radiata cv. Kalyan were used as trap plants to isolate bradyrhizobia. All the Nepalese soybean and mungbean isolates characterized in this study were slow growers and were assigned to the Bradyrhizobium genus based on their molecular characterization. We found that 46% of the isolates from soybean analyzed in the present study were phylogenetically related to B. elkanii, 21% were related to B. japonicum, and 8% were related to B. yuanmingense. Phylogenetic analyses also revealed three novel lineages comprising 25% of the analyzed population. Similarly, we found 50% of the isolates from the mungbean were phylogenetically related to B. yuanmingense, 13% were related to B. japonicum, 8% were related to B. elkanii, and 29% were found with novel phylogenetic origin. Furthermore, we found that most mungbean rhizobial genotypes were conserved across agro-ecological regions of Nepal. All the strains from tropical Terai region belonged to B. yuanmingense or a novel lineage of B. yuanmingense, and dominance of B. japonicum related strains observed in the Hill region. Our results indicate that there is higher genetic diversity of Bradyrhizobium strains in the temperate and subtropical region than in the tropical region. Though nifD genes are considered as high homology genes, considerable nifD gene sequence divergence of Nepalese strains with known reference strains were noticed. We, for the first time, analyzed nifD genes from B. yuanmingense in this study. We found nifD genes in B. yuanmingense isolated from soybean and mungbean are far different from other Bradyrhizobium species. 33 2011
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