Genomic Diversity of <i>Bradyrhizobium</i> from the Tree Legumes <i>Inga</i> and <i>Lysiloma</i> (Caesalpinioideae-Mimosoid Clade)

Abstract

We identified diverse bradyrhizobia having distinct ERIC-PCR genomic fingerprints from native American trees Inga vera and Lysiloma spp. In addition, two nodule isolates recovered from Lysiloma divaricatum seedlings inoculated with soil from the tropical house of a UK botanical garden were also identified as Bradyrhizobium. Genomes were obtained (with sizes around 9 Mb each) from nine Inga and Lysiloma bradyrhizobial isolates; plasmids were detected in two of the Inga strains analyzed. Average Nucleotide Identity of whole genomes revealed five novel Bradyrhizobium genomospecies from Mexican trees, while the UK isolates were identified as Bradyrhizobium cajani and Bradyrhizobium brasilense. Inga vera and Lysiloma isolates, despite their genetic distances and different hosts, shared a common set of nod genes that suggested that I. vera and Lysiloma bradyrhizobia produce fucosylated, methylated and carbamylated lipochitooligosaccharides. Uptake hydrogenase hup, hyp and secretion system genes were found in some of the isolates. Lysiloma strains were found to be ineffective on I. vera. Some of the isolates may be used as plant inoculants.

Keywords

• symbiosis
• nitrogen fixation
• <i>nod</i> genes
• genomospecies
• symbiosis island