Transformações do nitrogênio associadas a bactérias endofíticas de bananeira

Abstract

The present study aimed to characterize the metabolic reactions and genes associated with transformation of nitrogen with endophytic bacteria of banana. The study was conducted in the premises of the Universidade Estadual of Montes Claros (UNIMONTES), at the campus of Janaúba, North region of Minas Gerais State. The identification of genus and species levels was performed by partial sequencing of the 16S rDNA region. The assimbiotic nitrogen fixation in vitro, nitrate reduction and urease activity were evaluated. The molecular study of the genes involved in nitrogenase enzymes and nitrite reductase was still held. Biochemical tests were performed in a completely randomized design, the treatments consisted of 40 bacterial isolates with three repetitions. After partial sequencing of the 16S rDNA, 40 sequences were obtained with good quality. Sequence analysis revealed that the strains are spread over four Bacillus, Rhizobium, Klebsiella and Enterobacter genres. The genus Bacillus is what occurred more frequently (92, 5%). Compared to other genres, there was only one representative of each gender (2, 5%). Ten species of the genus Bacillus were identified: B. subtilis (11 isolates), B.pumilus (10 isolates), B.safensis (5 isolates), B. altitudinus (3 isolates), B.thuringienses (2) isolates), B. cereus (2 isolates), B. amyloliquefaciens (1 isolado) B.aerophilus (1 isolate), B. axarquienses (1 isolate) and B. megaterium (1 isolate). Being the species B subtilis and B. pumilus predominant over the others, they represented 27,5% and 25%, respectively. Considering all the results of biochemical tests was observed that only three isolates (13, 105 and 171) had multiple abilities: growth amid NFb, nitrate reduction, and urease production. Isolates are pertecentes gender and species Bacillus subtilis, and thuringienses amyloliquefaciens. Four isolates identified by the numbers 20, 29, 112 and 115 demonstrated the ability to grow in the NFB and nitrate reduction, whereas the others showed abilities to reduce nitrate to nitrite and urease activity. Among the isolates 12,5% amplified the nifH: B subtilis Solates (13, 86, 93 and 112); B. pumilus, isolated 61; B. safensis isolated B. altitudinus 137 and 173. To isolate the gene NIRK 7,5% of the isolates amplified this region, especially the isolated 22, 61 and 137 of the species K. pneumoniae, B. pumilus and B. safensis, respectively. Regarding the nirs gene, only 5% of isolates for the region amplified, both from the genus Bacillus isolates 18 and 193 that correspond to the species axarquienses and B. aerophilus. The results of the amplification of the nifH together with the results obtained for growth in medium NFB and acetylene reduction, indicating the low potential for biological nitrogen fixation by isolated, although some characteristics have isolated fasteners do not act as such developing instead the route of denitrification. The positive for nitrate reduction and urease production determine the metabolic profile of banana endophytic bacteria isolated in the northern region of Minas Gerais, which will make possible the proper management of the same. Based on these results and the different skills presented by endophytic bacteria can be suggested that one of the strategies considered in a future study focuses on the implementation and evaluation of endophytic bacteria isolated directly in micropropagated of banana thee.