The ACC-Deaminase Producing Bacterium <i>Variovorax</i> sp. CT7.15 as a Tool for Improving <i>Calicotome villosa</i> Nodulation and Growth in Arid Regions of Tunisia
2020
Khouloud Bessadok | Salvadora Navarro-Torre | Eloísa Pajuelo | Enrique Mateos-Naranjo | Susana Redondo-Gómez | Miguel Ángel Caviedes | Amira Fterich | Mohamed Mars | Ignacio D. Rodríguez-Llorente
<i>Calicotome villosa</i> is a spontaneous Mediterranean legume that can be a good candidate as pioneer plants to limit regression of vegetation cover and loss of biodiversity in Tunisian arid soils. In order to grow legumes in such soils, pairing rhizobia and nodule associated bacteria (NAB) might provide numerous advantages. In this work, cultivable biodiversity of rhizobial symbionts and NAB in nodules of <i>C. villosa</i> plants growing in five arid regions of south Tunisia was characterized. Phylogenetic analysis using 16S rDNA gene, <i>dnak</i>, <i>recA</i> and <i>nodD</i> sequences separated nodule-forming bacteria in six clades associated to genera <i>Ensifer</i>, <i>Neorhizobium</i>, <i>Phyllobacterium</i> and <i>Rhizobium</i>. Among NAB, the strain <i>Variovorax</i> sp. CT7.15 was selected due to its capacity to solubilise phosphate and, more interestingly, its high level of aminocyclopropane-1-carboxylate deaminase (ACC deaminase) activity. <i>C. villosa</i> plants were inoculated with representative rhizobia of each phylogenetic group and co-inoculated with the same rhizobia and strain CT7.15. Compared with single rhizobia inoculation, co-inoculation significantly improved plant growth and nodulation, ameliorated plant physiological state and increased nitrogen content in the plants, independently of the rhizobia used. These results support the benefits of pairing rhizobia and selected NAB to promote legume growth in arid or degraded soils.
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