Endophytic bacteria (247 isolates) were randomly isolated from surface-sterilized stems of non-nodulated (Nod
-), wild-type nodulated (Nod
+), and hypernodulated (Nod
++) soybeans (
Glycine max [L.] Merr) on three agar media (R2A, nutrient agar, and potato dextrose agar). Their diversity was compared on the basis of 16S rRNA gene sequences. The phylogenetic composition depended on the soybean nodulation phenotype, although diversity indexes were not correlated with nodulation phenotype. The most abundant phylum throughout soybean lines tested was
Proteobacteria (58-79%).
Gammaproteobacteria was the dominant class (21-72%) with a group of
Pseudomonas sp. significantly abundant in Nod
+ soybeans. A high abundance of
Alphaproteobacteria was observed in Nod
- soybeans, which was explained by the increase in bacterial isolates of the families
Rhizobiaceae and
Sphingomonadaceae. A far greater abundance of
Firmicutes was observed in Nod
- and Nod
++ mutant soybeans than in Nod
+ soybeans. An impact of culture media on the diversity of isolated endophytic bacteria was also observed: The highest diversity indexes were obtained on the R2A medium, which enabled us to access
Alphaproteobacteria and other phyla more frequently. The above results indicated that the extent of nodulation changes the phylogenetic composition of culturable bacterial endophytes in soybean stems.
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