Abstract
The genetic diversity of bacterial populations nodulating
in five geographical sites from northern Tunisia was examined. Phylogenetic analyses of 50 isolates based on partial sequences of
and
grouped strains into seven clusters, five of which belong to the genus
(28 isolates), one to
(2 isolates), and one, remarkably, to
(20 isolates). The largest
cluster (17 isolates) grouped with the
species, and the other five clusters were close to different recently defined
species. Isolates close to
were obtained from nodules of plants from four of the five sites sampled. We carried out an in-depth phylogenetic study with representatives of the seven clusters using sequences from housekeeping genes (
,
,
,
, and
) and obtained consistent results. A phylogeny based on the sequence of the symbiotic gene
identified four groups, three formed by
isolates and one by the
and
isolates. Symbiotic behaviors of the representative strains were tested, and some congruence between symbiovars and symbiotic performance was observed. These data indicate a remarkable diversity of
root nodule symbionts in northern Tunisia, including strains from the
,
, and
families, in contrast with those of the rhizobial populations nodulating lupines in the Old World, including
from other Mediterranean areas, which are nodulated mostly by
strains.
is a legume broadly distributed in the Mediterranean region and plays an important role in soil fertility and vegetation coverage by fixing nitrogen and solubilizing phosphate in semiarid areas. Direct sowing to extend the distribution of this indigenous legume can contribute to the prevention of soil erosion in pre-Saharan lands of Tunisia. However, rhizobial populations associated with
are poorly understood. In this context, the diversity of endosymbionts of this legume was investigated. Most
species are nodulated by
strains. This work showed that about half of the isolates from northern Tunisian soils were in fact
symbionts, but the other half were found unexpectedly to be bacteria within the genera
and
These unusual endosymbionts may have a great ecological relevance. Inoculation with the appropriate selected symbiotic bacterial partners will increase
survival with consequent advantages for the environment in semiarid areas of Tunisia.