LAUSR

The genetic diversity of bacterial populations’ nodulating Retama sphaerocarpa grown in the soils of Maamora cork forest (Morocco) was examined. ERIC-PCR fingerprinting of 30 strains distributed them in 2 groups, of which a representative strain from each group was studied by multilocus sequence analysis of the 16S rRNA, atpD, and gyrB genes. The two representative strains RSM25 and RSM32, grouped with “Microvirga tunisiensis”. This is the first description of Retama nodule bacteria as members of the genus Microvirga. A nodC-based phylogeny confirmed that the two representative strains RSM25 and RSM32 are affiliated with symbiovar mediterranense. The 2 strains were capable of nodulating not only R. sphaerocarpa but also R. monosperma, R. dasycarpa and L. luteus, and unable to nodulate Phaseolus vulgaris, Vachellia gummifera, Cicer arietinum, Vigna unguiculata and Glycine max. The inoculation of R. sphaerocarpa with RSM25 or RSM32 produced a 1.22-, and 1.36-fold increase in the dry weight of the plants compared to those grown in the presence of 0.05% KNO3. The 2 strains used monosaccharides and disaccharides as the sole C source, but fructose, glucose, galactose, arabinose and starch were not used. They were unable to grow on glycine as a N source. Phosphate solubilization and siderophore production was not detected, but IAA or IAA-related compounds were produced. The alkaline pH of the sampling site soil in the Maamora forest where Retama grows could explain why Microvirga was the dominant species in the root nodules of the plants.