Pasture degradation can cause changes in diazotrophic bacterial communities. Thus, this study aimed to evaluate the culturable and total diazotrophic bacterial community, associated with regions of the rhizosphere and roots of Brachiaria decumbens Stapf. pastures in different stages of degradation. Samples of roots and rhizospheric soil were collected from slightly, partially, and highly degraded pastures. McCrady's table was used to obtain the Most Probable Number (MPN) of bacteria per gram of sample, in order to determine population density and calculate the Shannon-Weaver diversity index. The diversity of total diazotrophic bacterial community was determined by the technique of Denaturing Gradient Gel Electrophoresis (DGGE) of the nif H gene, while the diversity of the culturable diazotrophic bacteria was determined by the Polymerase Chain Reaction (BOX-PCR) technique. The increase in the degradation stage of the B. decumbens Stapf. pasture did not reduce the population density of the cultivated diazotrophic bacterial community, suggesting that the degradation at any degree of severity was highly harmful to the bacteria. The structure of the total diazotrophic bacterial community associated with B. decumbens Stapf. was altered by the pasture degradation stage, suggesting a high adaptive capacity of the bacteria to altered environments.

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This study aimed to bioprospect and select halotolerantes bacteria and promoting plant growth associated with the plant Atriplex nummularia L. in saline soils. For bioprospecting of bacteria, samples were collected in five niches and two field experiments located in Serra Talhada and Ibimirim, Pernambuco, Brazil. After collecting the material it was performed the isolation and selection of bacteria based on plant growth promotion mechanisms. 107 bacterial salt tolerant isolates were obtained in which the population density of bacteria was higher in the rhizosphere (10 7 CFU g -1 soil), the cultivated soil (10 6 CFU g -1 soil) and uncultivated soil (10 5 CFU g -1 soil). For the solubilization rate of inorganic phosphate was obtained 65 and 25% positives isolated in 0 to 5% NaCl concentration, respectively. For the characteristics of biological fixation nitrogen, indole acetic acid production, exopolysaccharides and quorum sensing molecule, reached up to 87 percent; 100; 83.33 and 96.66% of the bacteria, respectively. Therefore, the bacterial isolates UAGAt 89 and UAGAt 101 expressed greater tolerance to salinity when analyzed in relation to the characteristics that promote plant growth, making it promising for future studies in order to contribute to the development of Atriplex plants and rehabilitation of soil affected by salts.

2018. Diazotrophic bacteria isolated from Brachiaria spp.: genetic and physiological diversity. Cien. Inv. Agr. 45(3): 277-289.Grass from the genus Brachiaria spp. predominates in pastures with low fertile soils. This scenario highlights the importance of the association with microorganisms to foster plant growth, which becomes essential to the successful establishment of this forage in such environments. This study aimed to evaluate the genetic variability and identify the mechanisms of plant growth promotion, in vitro, of bacteria associated with Brachiaria decumbens Stapf. and Brachiaria humidicola (Rendle.) Schweickerdt in Pernambuco, Brazil. We evaluated 20 isolates of diazotrophic bacteria obtained from the endophyte or rhizosphere communities. The genetic characteristics were determined via sequencing the 16S rRNA region, which allowed us to identify ten different bacterial genera: Bacillus sp., Burkholderia sp., Enterobacter sp., Klebsiella sp., Microbacterium sp., Pantoea sp., Ralstonia sp., Rhizobium sp., Sinomonas sp., and Sphingomonas sp., with a specificity of the genus Rhizobium sp. to Brachiaria decumbens Stapf.. The phenotypic and functional characteristics revealed that 100% of the bacterial strains produced indol-3-acetic acid (IAA) with the addition of L-tryptophan, and 60% presented IAA production independent of the L-tryptophan pathway. We also detected that 70% of the isolated bacteria possessed the capacity to solubilize phosphorus. The analysis of the enzymatic output revealed that 30% of the bacterial isolates produced cellulase, 60% produced pectate lyase, 15% produced polygalacturonase, and 30% produced amylase. We also detected the production of N-acyl homoserine lactones in 65% of bacterial strains. In summary, our results showed that plants of B. decumbens Stapf. and B. humidicola (Rendle.) Schweickerdt interacted with different bacterial genera capable of promoting plant growth.