Multilocus sequence analysis of root nodule isolates from Lotus arabicus (Senegal), Lotus creticus, Argyrolobium uniflorum and Medicago sativa (Tunisia) and description of Ensifer numidicus sp. nov. and Ensifer garamanticus sp. nov.

Nine isolates from Argyrolobium uniflorum, Lotus creticus , Medicago sativa (Tunisia) and Lotus arabicus (Senegal) were analysed by multilocus sequence analysis (MLSA) of five housekeeping genes (recA, atpD, glnA, gltA and thrC), the 16S rRNA gene and the nodulation gene nodA. Analysis of the individual and concatenated gene sequences demonstrated that the nine new strains constituted three stable, well-supported (bootstrap and gene sequence similarity values) monophyletic clusters, A, B and C, all belonging to the branch of the genus Ensifer, regardless of the phylogenetic reconstruction method used (maximum likelihood, maximum-parsimony, neighbour-joining). The three groups were further characterized by API 100 auxanographic tests, host specificity and nodA gene sequence analysis. On the basis of these data, clusters A and C are suggested as representing two novel species within the genus Ensifer, for which the names Ensifer numidicus sp. nov. (type strain ORS 1407(T)=LMG 24690(T)=CIP 109850(T)) and Ensifer garamanticus sp. nov. (type strain ORS 1400(T)=LMG 24692(T)=CIP 109916(T)) are proposed. The cluster B strains were assigned to Ensifer adhaerens genomovar A.

Phenotypic and genotypic diversity of Genista saharae microsymbionts from the infra-arid region of Tunisia.

AIMS: Genista saharae, indigenous of Sahara, is a spontaneous shrub that plays an important ecological role for the preservation and fertility of poor and eroded soils. This legume has not been examined for its root nodule bacteria. The taxonomic diversity of bacteria from root nodules of G. saharae growing in the infra-arid region of Tunisia was investigated. METHODS AND RESULTS: A total of 28 bacterial strains isolated from root nodules of G. saharae grown in Tunisian soil were characterized using a polyphasic approach including phenotypic characteristics, PCR-RFLP of 16S rDNA and 16S rRNA gene sequencing. It was found that new isolates are diverse and affiliated to Ensifer (75%), Rhizobium (10%) and Phyllobacterium (15%). The Phyllobacterium isolates lacked the capacity for nodule formation on this plant. CONCLUSIONS: Genista saharae formed nodules with diverse rhizobia in Tunisian soils. Furthermore, our results support the presence of non-nodulating commensal strains (Phyllobacterium) in legumes nodule. SIGNIFICANCE AND IMPACT OF THE STUDY: This study is the first report on the characterization of G. saharae microsymbionts in Tunisia.