Affiliation:
1. Department of Crop Sciences, Tshwane University of Technology, Pretoria, South Africa
2. Department of Chemistry, Tshwane University of Technology, Arcadia Campus, Pretoria, South Africa
Abstract
ABSTRACT
Cowpea derives most of its N nutrition from biological nitrogen fixation (BNF) via symbiotic bacteroids in root nodules. In Sub-Saharan Africa, the diversity and biogeographic distribution of bacterial microsymbionts nodulating cowpea and other indigenous legumes are not well understood, though needed for increased legume production. The aim of this study was to describe the distribution and phylogenies of rhizobia at different agroecological regions of Mozambique using PCR of the BOX element (BOX-PCR), restriction fragment length polymorphism of the internal transcribed spacer (ITS-RFLP), and sequence analysis of ribosomal, symbiotic, and housekeeping genes. A total of 122 microsymbionts isolated from two cowpea varieties (IT-1263 and IT-18) grouped into 17 clades within the BOX-PCR dendrogram. The PCR-ITS analysis yielded 17 ITS types for the bacterial isolates, while ITS-RFLP analysis placed all test isolates in six distinct clusters (I to VI). BLAST
n
sequence analysis of 16S rRNA and four housekeeping genes (
glnII
,
gyrB
,
recA
, and
rpoB
) showed their alignment with
Rhizobium
and
Bradyrhizobium
species. The results revealed a group of highly diverse and adapted cowpea-nodulating microsymbionts which included
Bradyrhizobium pachyrhizi
,
Bradyrhizobium arachidis
,
Bradyrhizobium yuanmingense
, and a novel
Bradyrhizobium
sp., as well as
Rhizobium tropici
,
Rhizobium pusense
, and
Neorhizobium galegae
in Mozambican soils. Discordances observed in single-gene phylogenies could be attributed to horizontal gene transfer and/or subsequent recombinations of the genes. Natural deletion of 60 bp of the
gyrB
region was observed in isolate TUTVU7; however, this deletion effect on DNA gyrase function still needs to be confirmed. The inconsistency of
nifH
with core gene phylogenies suggested differences in the evolutionary history of both chromosomal and symbiotic genes.
IMPORTANCE
A diverse group of both
Bradyrhizobium
and
Rhizobium
species responsible for cowpea nodulation in Mozambique was found in this study. Future studies could prove useful in evaluating these bacterial isolates for symbiotic efficiency and strain competitiveness in Mozambican soils.
Funder
Bill and Melinda Gates Foundation
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
51 articles.
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