Coexistence of Burkholderia, Cupriavidus, and Rhizobium sp. nodule bacteria on two Mimosa spp. in Costa Rica

Abstract

rRNA gene sequencing and PCR assays indicated that 215 isolates of root nodule bacteria from two Mimosa species at three sites in Costa Rica belonged to the genera Burkholderia, Cupriavidus, and Rhizobium. This is the first report of Cupriavidus sp. nodule symbionts for Mimosa populations within their native geographic range in the neotropics. Burkholderia spp. predominated among samples from Mimosa pigra (86% of isolates), while there was a more even distribution of Cupriavidus, Burkholderia, and Rhizobium spp. on Mimosa pudica (38, 37, and 25% of isolates, respectively). All Cupriavidus and Burkholderia genotypes tested formed root nodules and fixed nitrogen on both M. pigra and M. pudica, and sequencing of rRNA genes in strains reisolated from nodules verified identity with inoculant strains. Inoculation tests further indicated that both Cupriavidus and Burkholderia spp. resulted in significantly higher plant growth and nodule nitrogenase activity (as measured by acetylene reduction assays) relative to plant performance with strains of Rhizobium. Given the prevalence of Burkholderia and Cupriavidus spp. on these Mimosa legumes and the widespread distribution of these plants both within and outside the neotropics, it is likely that both beta-proteobacterial genera are more ubiquitous as root nodule symbionts than previously believed.

FIG. 1.

Bootstrap majority-rule consensus tree from maximum likelihood analysis of 16S rRNA genes from Costa Rican Burkholderia and Cupriavidus strains (shown in bold) and other β-Proteobacteria. Legume nodule symbionts are marked with an asterisk. Numbers near branches are bootstrap percentages for maximum parsimony (top), neighbor joining (center), and maximum likelihood (bottom) analyses. For nodule strains, the country of origin is also indicated (CR, Costa Rica).

FIG. 2.

Nodulation (top) and acetylene reduction activity (bottom) of Mimosa pudica (solid bars) and Mimosa pigra (hatched bars) inoculated with Cupriavidus (genotypes G, H, and I1) and Burkholderia (genotypes C and E). Data are means + 1 standard deviation.