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c Among the leguminous trees native to Uruguay, Parapiptadenia rigida (Angico), a Mimosoideae legume, is one of the most promising species for agroforestry. Like many other legumes, it is able to establish symbiotic associations with rhizobia and belongs to the group known as nitrogen-fixing trees, which are major components of agroforestry systems. Information about rhizobial symbionts for this genus is scarce, and thus, the aim of this work was to identify and characterize rhizobia associated with P. rigida. A collection of Angico-nodulating isolates was obtained, and 47 isolates were selected for genetic studies. According to enterobacterial repetitive intergenic consensus PCR patterns and restriction fragment length polymorphism analysis of their nifH and 16S rRNA genes, the isolates could be grouped into seven genotypes, including the genera Burkholderia, Cupriavidus, and Rhizobium, among which the Burkholderia genotypes were the predominant group. Phylogenetic studies of nifH, nodA, and nodC sequences from the Burkholderia and the Cupriavidus isolates indicated a close relationship of these genes with those from betaproteobacterial rhizobia (beta-rhizobia) rather than from alphaproteobacterial rhizobia (alpha-rhizobia). In addition, nodulation assays with representative isolates showed that while the Cupriavidus isolates were able to effectively nodulate Mimosa pudica, the Burkholderia isolates produced white and ineffective nodules on this host. Parapiptadenia rigida (Benth.) Brenan, which is also known by its vernacular names Angico, Angico vermelho, and Gurucaia, belongs to the tribe Mimoseae within the Mimosoideae subfamily of the Fabaceae (Leguminosae) (5,26,27,38). It is native to southern South America (south Brazil, Argentina, Paraguay, and Uruguay), where it can be found as one of the tallest species in the canopy of riverside forests, where it can reach heights of approximately 30 m and breast height diameters of from 30 to 120 cm. The wild tree is currently exploited by the locals owing to its economic value, although commercial cultivation of P. rigida has never been developed in Uruguay. Its main economic value is based on the excellence of its timber, which is appreciated for its high density (0.74 to 0.98 g/cm 3 ) and natural durability (26). It is mostly used for high-quality furniture, house construction, carpentry, and fire wood, and the reddish brown parquet floors built with its timber are deeply valued. Other reported uses are as a source of gums, tannins, and essential oils as well as for medicinal purposes (14, 37). Indeed, it is much appreciated by people in Brazil for its medicinal qualities and is duly included in the Brazilian Pharmacopeia.This heliophyte species is part of the forest succession during the first steps of recovery of degraded areas, as it can grow under adverse and low-soil-fertility conditions. Its ability to establish a nitrogen-fixing association with rhizobia is well documented (18)(19)(20)32), but information about the rhizobia associated with this leguminous...

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The genome of Azoarcus olearius DQS-4 , a N -fixing Betaproteobacterium isolated from oil-contaminated soil in Taiwan, was sequenced and compared with other Azoarcus strains. The genome sequence showed high synteny with Azoarcus sp. BH72, a model endophytic diazotroph, but low synteny with five non-plant-associated strains (Azoarcus CIB, Azoarcus EBN1, Azoarcus KH32C, A. toluclasticus MF63 and Azoarcus PA01). Average Nucleotide Identity (ANI) revealed that DQS-4 shares 98.98% identity with Azoarcus BH72, which should now be included in the species A. olearius. The genome of DQS-4 contained several genes related to plant colonization and plant growth promotion, such as nitrogen fixation, plant adhesion and root surface colonization. In accordance with the presence of these genes, DQS-4 colonized rice (Oryza sativa) and Setaria viridis, where it was observed within the intercellular spaces and aerenchyma mainly of the roots. Although they promote the growth of grasses, the mechanism(s) of plant growth promotion by A. olearius strains is unknown, as the genomes of DQS-4 and BH72 do not contain genes for indole acetic acid (IAA) synthesis nor phosphate solubilization. In spite of its original source, both the genome and behaviour of DQS-4 suggest that it has the capacity to be an endophytic, nitrogen-fixing plant growth-promoting bacterium.

Sweet sorghum (Sorghum bicolor) is a multipurpose crop used as a feedstock to produce bioethanol, sugar, energy, and animal feed. However, it requires high levels of N fertilizer application to achieve the optimal growth, which causes environmental degradation. Bacterial endophytes, which live inside plant tissues, play a key role in the health and productivity of their host. This particular community may be influenced by different agronomical practices. The aim of the work was to evaluate the effects of N fertilization on the structure, diversity, abundance, and composition of endophytic and diazotrophic bacterial community associated with field-grown sweet sorghum. PCR-DGGE, quantitative PCR, and high-throughput sequencing were performed based on the amplification of rrs and nifH genes. The level of N fertilization affected the structure and abundance but not the diversity of the endophytic bacterial communities associated with sweet sorghum plants. This effect was pronounced in the roots of both bacterial communities analyzed and may depend on the physiological state of the plants. Specific bacterial classes and genera increased or decreased when the fertilizer was applied. The data obtained here contribute to a better understanding on the effects of agronomical practices on the microbiota associated with this important crop, with the aim to improve its sustainability.

The aims of this study were to isolate, characterize and identify the native culturable putative endophytic bacterial community associated with tall fescue (Festuca arundinacea) cv. SFRO Don Tomás, cultivated in Uruguay, and to study the effects of inoculation on cv. SFRO Don Tomás and the commercial cv. Tacuabé. A total of 342 isolates were collected from surface-sterilized roots, stems and seeds of healthy cv. SFRO Don Tomás. The functional ability of the isolates to produce indole, to solubilize minerals (P, Fe, K) and to biologically fix molecular nitrogen (N 2 ) was determined. Several infection traits, such as the ability to produce proteases, peroxidases, cellulases and hemicellulases, were identified in the isolates. Selected bacterial isolates were identified by 16S rRNA sequencing and shown to belong to a broad spectrum of genera, including Bacillus , Microbacterium, Curtobacterium, Streptomyces, Acidovorax, Variovorax, Acinetobacter, Pseudomonas, Pantoea, Rhanella and Xanthomonas. Plant growth promotion assays shown that ten isolates were able to promote the growth of cv. SFRO Don Tomás under gnotobiotic conditions, thereby highlighting the potential of these isolates in biotechnological applications as inoculant for this cultivar which is highly adapted to dry and cold seasons.

Aim Sugarcane is a multipurpose crop primarily used to produce sugar, energy and bioethanol. It requires high amounts of Nfertilization for optimal growth, which increases production costs and environmental degradation. The contribution of biological nitrogen fixation to Uruguayan commercial sugarcane cultivars was demonstrated previously, and diazotrophic bacteria that were isolated from the stems were characterized and identified. From this collection, the isolate UYSO10 related to the Kosakonia genus (formerly Enterobacter) was described as a plant growth-promoting endophyte of sugarcane plants. Purpose To evaluate the effect of the inoculation of wild-type and nitrogenase-deficient strains of Kosakonia sp. UYSO10 on sugarcane growth promotion under non-sterile conditions. Methods Kosakonia sp. UYSO10 was inoculated onto sugarcane setts for plant growth promotion greenhouse experiments. Single and double mutants resulting to the nitrogenase-encoding genes (nifH, anfH) were constructed, and the phenotypes were evaluated in vitro and in vivo. Results Kosakonia sp. UYSO10 is able to promote sugarcane growth under non-sterile conditions, that strain UYSO10 harbors two functional nitrogenases and the inactivation of both nitrogenase-encoding genes diminish its capacity of promoting growth on sugarcane. Conclusion All together, the results obtained showed that the biological nitrogen fixation ability of Kosakonia sp. UYSO10 is required for sugarcane growth promotion.

The application of new agricultural technologies to attain sustainable production systems is necessary. The use of plant growth-promoting bacteria to improve plant growth and health has been studied for decades. This work aimed to isolate diazotrophic endophytic bacteria associated with sweet sorghum plants and study the interaction of their inoculation in combination with chemical N-fertilization on different sorghum cultivars. A bacterial collection of 181 isolates was constructed and characterized in vitro and in vivo. From that, the strains Enterobacter sp. UYSB89 and Kosakonia sp. UYSB139 were nifH+, produce IAA, defined as true endophytes and able to promote growth of two sweet sorghum under greenhouse conditions. The evaluated cultivars responded differentially to bacterial inoculation, the nitrogen fertilization doses and their interaction. Thus, plant growth is a multifactorial consequence of the interrelation between crop practices and the plant genotypes. This knowledge is a valuable factor in terms of understanding plant-bacteria endophyte interactions to preserve environmental sustainability during the implementation of agronomic practices.