Affiliation:
1. Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidin, CSIC, Granada, Spain
2. Unidad de Biotecnología 3, Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús (IIB-INTECH), UNSAM-CONICET, Chascomús, Buenos Aires, Argentina
Abstract
ABSTRACT
A total of 103 root nodule isolates were used to estimate the diversity of bacteria nodulating
Lotus tenuis
in typical soils of the Salado River Basin. A high level of genetic diversity was revealed by repetitive extragenic palindromic PCR, and 77 isolates with unique genomic fingerprints were further differentiated into two clusters, clusters A and B, after 16S rRNA restriction fragment length polymorphism analysis. Cluster A strains appeared to be related to the genus
Mesorhizobium
, whereas cluster B was related to the genus
Rhizobium
. 16S rRNA sequence and phylogenetic analysis further supported the distribution of most of the symbiotic isolates in either
Rhizobium
or
Mesorhizobium
: the only exception was isolate BA135, whose 16S rRNA gene was closely related to the 16S rRNA gene of the genus
Aminobacter.
Most
Mesorhizobium
-like isolates were closely related to
Mesorhizobium amorphae
,
Mesorhizobium mediterraneum
,
Mesorhizobium tianshanense
, or the broad-host-range strain NZP2037, but surprisingly few isolates grouped with
Mesorhizobium loti
type strain NZP2213.
Rhizobium
-like strains were related to
Rhizobium gallicum
,
Rhizobium etli
, or
Rhizobium tropici
, for which
Phaseolus vulgaris
is a common host. However, no
nodC
or
nifH
genes could be amplified from the
L. tenuis
isolates, suggesting that they have rather divergent symbiosis genes. In contrast,
nodC
genes from the
Mesorhizobium
and
Aminobacter
strains were closely related to
nodC
genes from narrow-host-range
M. loti
strains. Likewise,
nifH
gene sequences were very highly conserved among the Argentinian isolates and reference
Lotus
rhizobia. The high levels of conservation of the
nodC
and
nifH
genes suggest that there was a common origin of the symbiosis genes in narrow-host-range
Lotus
symbionts, supporting the hypothesis that both intrageneric horizontal gene transfer and intergeneric horizontal gene transfer are important mechanisms for the spread of symbiotic capacity in the Salado River Basin.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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