Diversidade fenotípica, genética e simbiótica de bactérias isoladas de nódulos de diferentes leguminosas florestais em viveiro

Abstract

Mining and mineral dressing activities have a social and economic importance, but they canalter the environment. The study on the diversity and biotechnological application of nitrogen-fixing bacteria, which play a role on promoting plant growth are an alternative to mitigate some mining impacts. Thus, the aim of this work was to evaluate the genotypic, phenotypic, and symbiotic diversity of nodulating bacteria that establishes root symbioses with legume plants grown in a greenhouse in the mining area. For this purpose, the nodules were collected in the greenhouse belonging to Mina de Córrego do Meio, ownership of VALE, in Sabará municipality. In the greenhouse, there were 20 legume plant species, which 11 plant species had nodules. They were smashed in petri dishes with 79 culture medium.The morphotypes obtained were isolated and cultural characterized.After wards a trial was performed to authenticate and evaluate the isolates nitrogen fixing efficiency in symbiosis with Siratro (Macroptilium atropurpureum). The trial was carried out in tubes containing sand and vermiculite (1:1). The treatments were obtained with the isolates plus the controls treatments without inoculation of the isolates (with high and low mineral nitrogen content) and with inoculation of the reference strains for siratro in biological nitrogen fixation UFLA 04-0212 and SEMIA 656.The experimental design was completed randomized with three replicates, conducted for 45 days. After this period, the following parameters were measured: nodules number, nodule dry weight, shoot, root and total dry weight, and relative efficiency. The data were analysed by variance analysis using Scott-Knott test at 5% of probability. The genetic diversity was verified by the genomic DNA extraction and partial sequencing of the16SrRNA gene. 92 isolates were obtained in pure culture, which 17 isolates shown fast growing acidifying the79 medium, 12 isolates shown fast growing without changing the pH of the 79 medium, 10 isolates shown fast growing alkalinizing the 79 medium, six isolates shown moderate growing acidifying the 79 medium, five isolates shown moderate growing without changing the pH of the 79 medium, seven isolates shown moderate growing alkalinizing the 79 medium, one isolate shown slow growing without changing the pH of the79 medium, and 33 isolates shown slow growing alkalinizing the 79 medium. In the authentication and symbiotic efficiency trial, 90% of the isolates nodulated, but their relative efficiency were variable, and 10% of the isolates promoted an increase statistically higher than the control with high N content, showing high biological nitrogen fixation efficiency. From 92 isolates, 37 strains were sequenced, representing different culture groups, which were identified belonging to Bradyrhizobium, Rhizobium, Burkholderia, Bacillus, Paenibacillus, Lysinibacillus, Bosea, Cohnella and Leifsonia genera. The results show a high genetic, phenotypic, and symbiotic diversity.