Diverse Bacteria Affiliated with the Genera Microvirga, Phyllobacterium, and Bradyrhizobium Nodulate Lupinus micranthus Growing in Soils of Northern Tunisia

作者：Msaddak Abdelhakim; Duran David; Rejili Mokhtar; Mars Mohamed; Ruiz Argueso Tomas; Imperial Juan; Palacios Jose; Rey Luis

来源：Applied and Environmental Microbiology, 2017, 83(6).

DOI：10.1128/AEM.02820-16

<jats:title>ABSTRACT</jats:title>
<jats:p>
The genetic diversity of bacterial populations nodulating
<jats:named-content content-type="genus-species">Lupinus micranthus</jats:named-content>
in five geographical sites from northern Tunisia was examined. Phylogenetic analyses of 50 isolates based on partial sequences of
<jats:italic>recA</jats:italic>
and
<jats:italic>gyrB</jats:italic>
grouped strains into seven clusters, five of which belong to the genus
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
(28 isolates), one to
<jats:named-content content-type="genus-species">Phyllobacterium</jats:named-content>
(2 isolates), and one, remarkably, to
<jats:named-content content-type="genus-species">Microvirga</jats:named-content>
(20 isolates). The largest
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
cluster (17 isolates) grouped with the
<jats:named-content content-type="genus-species">B. lupini</jats:named-content>
species, and the other five clusters were close to different recently defined
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
species. Isolates close to
<jats:named-content content-type="genus-species">Microvirga</jats:named-content>
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 (
<jats:italic>rrs</jats:italic>
,
<jats:italic>recA</jats:italic>
,
<jats:italic>glnII</jats:italic>
,
<jats:italic>gyrB</jats:italic>
, and
<jats:italic>dnaK</jats:italic>
) and obtained consistent results. A phylogeny based on the sequence of the symbiotic gene
<jats:italic>nodC</jats:italic>
identified four groups, three formed by
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
isolates and one by the
<jats:named-content content-type="genus-species">Microvirga</jats:named-content>
and
<jats:named-content content-type="genus-species">Phyllobacterium</jats:named-content>
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
<jats:named-content content-type="genus-species">L. micranthus</jats:named-content>
root nodule symbionts in northern Tunisia, including strains from the
<jats:named-content content-type="genus-species">Bradyrhizobiaceae</jats:named-content>
,
<jats:named-content content-type="genus-species">Methylobacteriaceae</jats:named-content>
, and
<jats:named-content content-type="genus-species">Phyllobacteriaceae</jats:named-content>
families, in contrast with those of the rhizobial populations nodulating lupines in the Old World, including
<jats:named-content content-type="genus-species">L. micranthus</jats:named-content>
from other Mediterranean areas, which are nodulated mostly by
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
strains.
</jats:p>
<jats:p>
<jats:bold>IMPORTANCE</jats:bold>
<jats:named-content content-type="genus-species">Lupinus micranthus</jats:named-content>
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
<jats:named-content content-type="genus-species">L. micranthus</jats:named-content>
are poorly understood. In this context, the diversity of endosymbionts of this legume was investigated. Most
<jats:named-content content-type="genus-species">Lupinus</jats:named-content>
species are nodulated by
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
strains. This work showed that about half of the isolates from northern Tunisian soils were in fact
<jats:named-content content-type="genus-species">Bradyrhizobium</jats:named-content>
symbionts, but the other half were found unexpectedly to be bacteria within the genera
<jats:named-content content-type="genus-species">Microvirga</jats:named-content>
and
<jats:named-content content-type="genus-species">Phyllobacterium</jats:named-content>
. These unusual endosymbionts may have a great ecological relevance. Inoculation with the appropriate selected symbiotic bacterial partners will increase
<jats:named-content content-type="genus-species">L. micranthus</jats:named-content>
survival with consequent advantages for the environment in semiarid areas of Tunisia.
</jats:p>

• 出版日期2017-3