Using sugar cane vinasse as a biofertilizer: effects on soil microbialcommunity due to periodical application

摘要

Lupinus, known by the common name of lupine or lupin, is a highly diverse genus of legume and is one of the most geographically widespread plant genera. Lupines can develop indeterminate nodules, known as lupinoid-nodules, in association with rhizobia, mainly belonging to the Bradyrhizobium genus. In this work, diversity of Uruguayan native rhizobia obtained from nodules of native Lupinus species growing in their natural habitat, was evaluated. We generated a collection of 109 isolates obtained from nodules of six, out of the seven, Uruguayan native species of lupine described for Uruguay: Lupinus albescens, Lupinus bracteolaris, Lupinus gibertianus, Lupinus lanatus, Lupinus multiflorus and Lupinus paraguariensis. According to the phylogeny of the 16 S rRNA gene, isolates belong to six well defined clusters within the Bradyrhizobium genus. Four of these clades include Bradyrhizobium species already known to be capable of nodulating Lupinus spp., while two clades include Bradyrhizobium species that have not been previously described as lupine nodule endosymbiont. Phylogeny of nifH and nodC genes was investigated in 21 selected isolates obtained from different lupine species and from different sites of collection. Our results indicate that the diversity of symbiotic genes is related to the continental origin of the lupine species rather than to the conserved 16 S rRNA molecular marker. Also interesting was the fact that symbiotic genes of rhizobia that nodulate the same native lupine species may have different evolutionary history. In conclusion, our results expand the knowledge about the phylogenetic diversity of Bradyrhizobium strains nodulating lupine species and provide insights in the biogeographic coevolution between lupines and its cognate rhizobia. Results obtained, together with the fact that the role of Nod factors in the recognition of lupine plant species by rhizobia has not yet been demonstrated, let us to hypothesize that nodC may be required for the development of a nitrogen-fixing nodule, but not for host plant recognition in the lupine-rhizobia association. Our results reinforce the hypothesis of a recent acquisition and evolution of symbiotic genes nifH and nodC in bacteria nodulating lupines.