Affiliation:
1. Embrapa Soja, Cx. Postal 231, 86001-970, Londrina, PR, Brazil; Departamento Microbiologia, Universidade Estadual de Londrina, Londrina, PR, Brazil; and Conselho Nacional de Desenvolvimento Científico e Tecnológico, Brasilia, DF, Brazil
Abstract
ABSTRACT
The importance of horizontal gene transfer (HGT) in the evolution and speciation of bacteria has been emphasized; however, most studies have focused on genes clustered in pathogenesis and very few on symbiosis islands. Both soybean (
Glycine max
[L.] Merrill) and compatible
Bradyrhizobium japonicum
and
Bradyrhizobium elkanii
strains are exotic to Brazil and have been massively introduced in the country since the early 1960s, occupying today about 45% of the cropped land. For the past 10 years, our group has obtained several isolates showing high diversity in morphological, physiological, genetic, and symbiotic properties in relation to the putative parental inoculant strains. In this study, parental strains and putative natural variants isolated from field-grown soybean nodules were genetically characterized in relation to conserved genes (by repetitive extragenic palindromic PCR using REP and BOX A1R primers, PCR-restriction fragment length polymorphism, and sequencing of the 16SrRNA genes), nodulation, and N
2
-fixation genes (PCR-RFLP and sequencing of
nodY-nodA
,
nodC
, and
nifH
genes). Both genetic variability due to adaptation to the stressful environmental conditions of the Brazilian Cerrados and HGT events were confirmed. One strain (S 127) was identified as an indigenous
B. elkanii
strain that acquired a
nodC
gene from the inoculant
B. japonicum
. Another one (CPAC 402) was identified as an indigenous
Sinorhizobium
(
Ensifer
)
fredii
strain that received the whole symbiotic island from the
B. japonicum
inoculant strain and maintained an extra copy of the original
nifH
gene. The results highlight the strategies that bacteria may commonly use to obtain ecological advantages, such as the acquisition of genes to establish effective symbioses with an exotic host legume.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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