Genetic and Genomic Diversity Studies of Acacia Symbionts in Senegal Reveal New Species of Mesorhizobium with a Putative Geographical Pattern

Abstract

Acacia senegal (L) Willd. and Acacia seyal Del. are highly nitrogen-fixing and moderately salt tolerant species. In this study we focused on the genetic and genomic diversity of Acacia mesorhizobia symbionts from diverse origins in Senegal and investigated possible correlations between the genetic diversity of the strains, their soil of origin, and their tolerance to salinity. We first performed a multi-locus sequence analysis on five markers gene fragments on a collection of 47 mesorhizobia strains of A. senegal and A. seyal from 8 localities. Most of the strains (60%) clustered with the M. plurifarium type strain ORS 1032T, while the others form four new clades (MSP1 to MSP4). We sequenced and assembled seven draft genomes: four in the M. plurifarium clade (ORS3356, ORS3365, STM8773 and ORS1032T), one in MSP1 (STM8789), MSP2 (ORS3359) and MSP3 (ORS3324). The average nucleotide identities between these genomes together with the MLSA analysis reveal three new species of Mesorhizobium. A great variability of salt tolerance was found among the strains with a lack of correlation between the genetic diversity of mesorhizobia, their salt tolerance and the soils samples characteristics. A putative geographical pattern of A. senegal symbionts between the dryland north part and the center of Senegal was found, reflecting adaptations to specific local conditions such as the water regime. However, the presence of salt does not seem to be an important structuring factor of Mesorhizobium species.

Global-level population genomics reveals differential effects of geography and phylogeny on horizontal gene transfer in soil bacteria

“…1A). The only named representative within this group occurs in clade 2, belonging to the species Mesorhizobium plurifarium, previously described to form nodules on tree and shrub legumes throughout the Old and New World tropics (51). These results suggest a pantropical distribution for this group, typically combined with characteristic local speciation.…”

The nitrogen-fixing Bradyrhizobium elkanii significantly stimulates root development and pullout resistance of Acacia confusa

“…into three groups, that is, Rhizobium-SinorhizobiumMesorhizobium (that is, A. Senegal, A. raddina and A. cyanophylla, respectively) (De Lajudie et al, 1994Khbaya et al, 1998), Bradyrhizobium (that is, A. albida, A. mangium and A. auriculiformis, respectively) (Galiana et al, 1990;Dupuy et al, 1994;Ferro et al, 2000), and two types of rhizobia (that is, A. Seyal) (Dreyfus and Dommergues, 1981). Diouf et al (2015) studied the genetic and genomic diversity of Acacia mesorhizobia symbionts in Senegal, and discovered three new species of Mesorhizobium. Wang et al (2008) indicated that rhizobia isolated from A. mangium in Fujian and Guangdong, China belongs to Mesorhizobium, whereas the strain isolated from A. confusa in Guangdong belonged to Bradyrhizobium.…”

“…Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Bradyrhizobium spp., Azorhizobium spp., and Mesorhizobium sp.) and form nitrogen-fixing nodules, which can fix nitrogen from air and supply nitrogen nutrient to trees for growth and development (Ferro et al, 2000;Zerhari et al, 2000;Dumroese et al, 2009;Ceccon et al, 2011;Diouf et al, 2015;Pereyra et al, 2015). Several studies have demonstrated that inoculation of seedlings (Oryza sativa, Glycine max and Zea mays) with rhizobial strains results in the change of root morphology, that is, increases in nodules, lateral roots, root hairs, root surface area, and total root length (Huang and Ladha, 1997;Ikeda, 1999;Souleimanov et al, 2002).…”

Permanent Draft Genome Sequences for Mesorhizobium sp. Strains LCM 4576, LCM 4577, and ORS3428, Salt-Tolerant, Nitrogen-Fixing Bacteria Isolated from Senegalese Soils

“…Mesorhizobium strains were sampled from soils with contrasted salt concentrations in Senegal (7), illustrating a large diversity of Mesorhizobium plurifarium as well as new species (MSP1-3) for which several genomes have been sequenced (8). Mesorhizobium sp.…”