Bactérias diazotróficas simbiontes de leguminosas em Canga e em área de mineração de ferro revegetada com capim

Abstract

The iron bands associated with rupestrian field, known as canga, displays a high degree of diversity and endemism. These communities of plants and microorganisms are adapted to unique and limiting environments, in which essential functions are performed, that results in soil maintenance. Diversity analyses in rupestrian fields, showed the dominance of Bradyrhizobium, Rhizobium and Burkholderia.Itis a legal requirement to restorethes ehabitats after detrimental impacts caused by mining activities. In this context, the lowcost technique of legume-root nodule symbiosis afforestation torecover degraded areas, has multiple benefits.The objective of this study was to identify species of associated diazotrophic bacteria, isolated from plants nodules in two areas that belongto the mining company Vale. Twoareaswere studied: rupestrian fiel donlateriticbench (canga), withpredominance of Mimosa calodendron; and a rehabilitated area revegetated with grasson the deposition of soil removedfrom the opening of an iron mining, withpredominantvegetation of Braquiaria and spontaneouspresence of the followingspecies: Mimosa setosa, Mimosa sensitiva, Crotalaria incana, Chamaecrista nictitans, Neotonia wightiStylosanthes sp, Crotalaria spectabilisand Crotalaria lanceolata.Nodulessamples were collectedatfive points in canga and 12 points were sampledonthe second area, collecting 5 nodules per plant. Nodules were stored in sterileflasks containingsilica gel to preventspoilage. The nodules were rehydrated and disinfected. After the incubationperiod, the colonies were purifiedand characterized morphologically. In order to verify the geneticdiversity, the extraction of genomic DNA and the partialsequencing of the 16S rRNA gene was performed. From 60 strains isolated, nine found in canga and 51onthe rehabilitation area; 24 were sequencedwhich are representatives ofseven froma total of nine cultural groups.Slow-growth bacteria (57%) were predominant, whilethere was apredominance ofalkalizing bacteria (73.5%). Most phenotipical diversity was found inM. setosawithsix cultural groups, followedby M. calodendronand Stylosanthes sp.whichformed five cultural groups each. C. incanahad the lowestdiversityaccording to its strains'culturalcharacteristics. Genetically, the two most common nodule bacteria found were Bradyrhizobium and Burkholderia, whilst genera of Paenibacillus, Pseudomonas, Bacillus, Variovorax, Leifsonia, Stenotrophomonas and Sphingomonas were the isolated bacterial endophytes strains.M. calodendron in canga and C. nictitans in the rehabilitation area showed the highest diversity. It is noteworthy, the occurrence of leguminosaenodulating bacteria (NFLNB) in both environments. This positive resultindicates a potential use of these bacteria in SoilRecovery Programs. Keywords: Biological nitrogen fixation. Diversity. Rupestrian fie