Phenotypic variation in Azospirillum brasilense Sp7 does not influence plant growth promotion effects |
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| Institution: | 1. Department of Plant Pathology and Microbiology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot 76100, Israel;2. Departamento de Biología Molecular, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, Río Cuarto, Córdoba, Argentina;1. Jiangsu Key Lab and Engineering Center for Solid Organic Waste Utilization, Jiangsu Collaborative Innovation Center for Solid Organic Waste Resource Utilization, National Engineering Research Center for Organic-based Fertilizers, Nanjing Agricultural University, 210095 Nanjing, China;2. Hainan Key Laboratory for Sustainable Utilization of Tropical Bio-resources, College of Agriculture, Hainan University, 570228 Haikou, China;1. School of Studies in Botany, Jiwaji University, Gwalior M.P., India;2. Department of Botany, SBBS University, Khiala Jalandhar Punjab, India;3. Department of Botany and Microbiology, King Saud University, Saudi Arabia;1. Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México Campus Morelos, Av. Universidad 1001, Col. Chamilpa, 62210 Cuernavaca, Morelos, Mexico;2. CONACYT, Unidad de Genómica Avanzada, Laboratorio Nacional de Genómica para la Biodiversidad (Langebio), Centro de Investigación y de Estudios Avanzados del IPN, Irapuato, Guanajuato, Mexico;1. Center of Plant, Soil Interaction and Natural Resources Biotechnology, Scientific and Technological Bioresource Nucleus (BIOREN), Universidad de La Frontera, Avenida Francisco Salazar, 01145, Temuco, Chile;2. Doctoral Program in Sciences of Natural Resources, Universidad de La Frontera, Avenida Francisco Salazar, 01145, Temuco, Chile;3. Biocontrol Research Laboratory–Center of Plant, Soil Interaction and Natural Resources Biotechnology; BIOREN, Universidad de La Frontera, Avenida Francisco Salazar, 01145, Temuco, Chile;4. Department of Botany and Zoology, Faculty of Science, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa;5. Soil and Plant Laboratory–Center of Plant, Soil Interaction and Natural Resources Biotechnology; BIOREN, Universidad de La Frontera, Avenida Francisco Salazar, 01145, Temuco, Chile |
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| Abstract: | The Azospirillum genus comprises free-living, plant growth-promoting, nitrogen-fixing bacteria found in the rhizosphere of plant roots. Azospirilla are able to promote plant growth mainly through improvement of root development. Bacterial surface components, such as extracellular polysaccharides and proteins, are involved in root colonization. Phase variation – or phenotypic variation – is one of the mechanisms by which microorganisms adapt to environmental changes. This phenomenon is characterized by the presence of a sub-population of the bacteria presenting a different phenotype relative to the major population. In this study we characterized phenotypic variation of Azospirillum brasilense Sp7. When plated on solid media, some A. brasilense colonies were shown to possess a much more mucoid morphology, producing 7.5–8 times more exopolysaccharide with different monosaccharide composition than the parental strain Sp7. The rate of appearance of this kind of variant colonies was 1 in 5000, in agreement with the accepted rate for the phase/phenotypic variation phenomenon. The variants were significantly more resistant to heat and UV-exposure than the parental strain and displayed genomic changes as seen by the different band patterns following ERIC-PCR, BOX-PCR and RAPD analyses. In plant inoculation experiments under greenhouse conditions, with maize, wheat, soybean and peanuts, the EPS overproducing variants performed as similar as the parental strain. Therefore, EPS overproduction did not confer an apparent advantage to A. brasilense in terms of induction of plant growth promotion. |
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| Keywords: | Phenotypic variation Phase variation Plant growth promotion Exopolysaccharides Genomic changes |
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