Abstract
Piliostigma reticulatum shrub is a native legume found in fallow areas in dry and semi-dry savanna soil and is used in intercropping systems. The aim was to understand the functioning of the rhizosphere, particularly the involvement of symbiotic and free living-N fixing bacteria. Soil extracts collected from P. reticulatum roots were sampled in two contrasting areas and endophytic bacterial communities were isolated using three trap host species (F. albida, A. bivenosa and V. seyal). Potential endophytic bacteria (PEB) were characterized by RFLP, nifH PCR and by 16S rRNA gene sequencing. The subsequent behavior of P. reticulatum was monitored in vitro by measuring leaf weight, biomass and chlorophyll content, after inoculation with PEB. This approach enabled isolation of 59 bacteria belonging to different genotypes. The most abundant genera were Cohnella (27.65%) among which 11 isolates clustered together and could represent a new species closely related to C. plantaginis. The other dominant genera were Paenibacillus (21.27%), Bradyrhizobium (14.89%) and Ensifer (8.5%). The nitrogen fixing gene (nifH) was detected in 21 strains and in particular, detected in a single isolate (PZS_S04) close to Cohnella xylanilytica. The strains PZS_S05 (Ensifer) and PZG_A18 (Cohnella) significantly increased certain parameters including shoot dry weight, shrub height at 90 days and photosynthetic activity (SPAD), compared to non-inoculated controls.The result obtained showed that soil under the influence of P. reticulatum roots harbored a specific diversity of endophytic bacteria including two free living-N fixing bacteria with the potential to improve the growth of P. reticulatum in natural conditions. Key words: Piliostigma reticulatum, microbiology, phylogeny, Potential endophytic bacteria (PEB), nitrogen-fixing bacteria.  
Highlights
The rhizosphere of legumes is a fertile zone due to the accumulation of different organic compounds released from their roots (Bowen and Rovira, 1999; Barea et al, 2005)
A total of 140 nodules were recovered at Sudano-Sahelian site (ZSS), of which 83 nodules came from the roots of F. albida, 43 nodules from the roots of V. seyal and only 14 from the roots of A. bivenosa
A total of 337 nodules formed on the roots of F. albida, 74 nodules on the roots of V. seyal and only one nodule formed on roots of A. bivenosa
Summary
The rhizosphere of legumes is a fertile zone due to the accumulation of different organic compounds released from their roots (Bowen and Rovira, 1999; Barea et al, 2005) For this reason, the soil under the influence of plant roots is very favorable for the growth and activity of microbial communities, which plays a significant role in carbon and nitrogen biogeochemical cycles (Vitousek and Howarth, 1991; Toal et al, 2000). The effects of the micro-environment formed by the plant rhizosphere on nitrogen-fixing symbiotic bacteria diversity remain unclear, in particular, on the subfamilies of Leguminosae such as Cercidoideae (LPWG, 2017) This new subfamily proposed by the Legume Phylogeny Working Group (LPWG) currently contains 12 genera (including Piliostigma genus) which mainly grow in tropical regions and have no root nodules (LPWG, 2017). Some works (James et al, 2000; Turner et al, 2013) suggest that endophytic bacteria may increase nitrogen fixation
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