Abstract
The aim of this work was to isolate and characterize, based on microbiological as well as molecular markers, bacteria within nodules of three native trees species from South America: Poecilanthe parviflora Benth (Lapachillo), Vachellia caven (Molina) Seigler & Ebinger (Espinillo), and Enterolobium contortisiliquum (Vell.) Morong (Timbó). In line with this, we isolated and characterized 15 bacteria from P. parviflora, 6 from V. caven and 1 from E. contortisiliquum. Among them we identified representatives of Bradyrhizobium sp. from E. contorsiliquum and P. parviflora, as well as of Ensifer sp. (Sinorhizobium) and Mesorhizobium sp. from V. caven. Also, other bacteria were found, like representatives of Bacillus sp., Microbacterium sp. and Curtobacterim sp., as well as Caulobacter sp., Dyella sp., Pseudomonas sp. and Enterobacter sp. Some of these isolates inhibited the growth of two fungal plant pathogens. So, nodules of these native legumes not only are occupied by highly diverse rhizobia but also by other bacteria that might promote plant growth.
Highlights
The Leguminosae (Fabaceae) is the third-largest plant family among angiosperms that comprises 20,000 species and 750 genera[1](2)(3)(4)
South American native tree legumes V. caven and P. parviflora harbour a great diversity of endophytic bacteria and alpha-rhizobia in their root nodules
E. contorsiliquum may establish a nitrogen-fixing symbiosis with Bradyrhizobium lianonginese, and P. parviflora may develop nodules with Bradyrhizobium spp strains that need to be studied further to determine the species
Summary
The Leguminosae (Fabaceae) is the third-largest plant family among angiosperms that comprises 20,000 species and 750 genera[1](2)(3)(4). Legumes establish a symbiotic association with Gramnegative soil bacteria known as rhizobia[1](5) that results in the development of nodules in roots and stems, where atmospheric nitrogen is reduced (fixed) to ammonia, that is assimilated by plants into organic compounds. The family of legumes is divided into three subfamilies that include mostly plants adapted to tropical regions, Cesalpinoidea, Papilinoidea and Mimosoidea; within the former one, only 11 genera form nitrogen-fixing nodules[1](6). Rhizobia vary in specificity as well as legumes, while some of them nodulate several hosts, others nodulate only one or two species. Several hosts are nodulated by several rhizobia, including both Alpha and Betaproteobacteria. The rhizobial strain-host genotype interaction is highly specific, to the point that two closely related species of plants are nodulated by different species of rhizobia[7]
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