NrcR, a new transcriptional regulator of Rhizobium tropici CIAT 899 involved in the Legume root-nodule symbiosis.

The establishment of nitrogen-fixing rhizobium-legume symbioses requires a highly complex cascade of events. In this molecular dialogue the bacterial NodD transcriptional regulators in conjunction with plant inducers, mostly flavonoids, are responsible for the biosynthesis and secretion of Nod factors which are key molecules for successful nodulation. Other transcriptional regulators related to the symbiotic process have been identified in rhizobial genomes, including negative regulators such as NolR. Rhizobium tropici CIAT 899 is an important symbiont of common bean (Phaseolus vulgaris L.), and its genome encompasses intriguing features such as five copies of nodD genes, as well as other possible transcriptional regulators including the NolR protein. Here we describe and characterize a new regulatory gene located in the non-symbiotic plasmid pRtrCIAT899c, that shows homology (46% identity) with the nolR gene located in the chromosome of CIAT 899. The mutation of this gene, named nrcR (nolR-like plasmid c Regulator), enhanced motility and exopolysaccharide production in comparison to the wild-type strain. Interestingly, the number and decoration of Nod Factors produced by this mutant were higher than those detected in the wildtype strain, especially under salinity stress. The nrcR mutant showed delayed nodulation and reduced competitiveness with P. vulgaris, and reduction in nodule number and shoot dry weight in both P. vulgaris and Leucaena leucocephala. Moreover, the mutant exhibited reduced capacity to induce the nodC gene in comparison to the wild-type CIAT 899. The finding of a new nod-gene regulator located in a non-symbiotic plasmid may reveal the existence of even more complex mechanisms of regulation of nodulation genes in R. tropici CIAT 899 that may be applicable to other rhizobial species

Effect of the presence of the plant growth promoting rhizobacterium (PGPR) Chryseobacterium balustinum Aur9 and salt stress in the pattern of flavonoids exuded by soybean roots

In this work we studied how biotic and abiotic stresses can alter the pattern of flavonoids exuded by Osumi soybean roots. A routine method was developed for the detection and characterization of the flavonoids present in soybean root exudates using HPLC-MS/MS. Then, a systematic screening of the flavonoids exuded under biotic stress, the presence of a plant growth promoting rhizobacterium, and salt stress was carried out. Results obtained indicate that the presence of Chryseobacterium balustinum Aur9 or 50 mM NaCl changes qualitatively the pattern of flavonoids exuded when compared to control conditions. Thus, in the presence of C. balustinum Aur9, soybean roots did not exude quercetin and naringenin and, under salt stress, flavonoids daidzein and naringenin could not be detected. Soybean root exudates obtained under saline conditions showed a diminished capacity to induce the expression of the nodA gene in comparison to the exudates obtained in the absence of salt. Moreover, lipochitooligosaccharides (LCOs) were not detected or weakly detected when Sinorhizobium fredii SMH12 was grown in the exudates obtained under salt stress conditions or under salt stress in the presence of C. balustinum Au9, respectively.Fil: Dardanelli, Marta Susana. Universidad de Sevilla. Facultad de Farmacia; España. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas, Fisicoquímicas y Naturales. Departamento de Biología Molecular. Sección Química Biológica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Manyani, Hamid. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: González Barroso, Sergio. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Rodríguez Carvajal, Miguel A.. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Gil Serrano, Antonio M.. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Espuny, Maria R.. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: López Baena, Francisco Javier. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Bellogín, Ramon A.. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Megías, Manuel. Universidad de Sevilla. Facultad de Farmacia; EspañaFil: Ollero, Francisco J.. Universidad de Sevilla. Facultad de Farmacia; Españ

On the impact of neighborhood selection strategies for recommender systems in LBSNs

Location-based social networks (LBSNs) have emerged as a new concept in online social media, due to the widespread adoption of mobile devices and location-based services. LBSNs leverage technologies such as GPS, Web 2.0 and smartphones to allow users to share their locations (check-ins), search for places of interest or POIs (Point of Interest), look for discounts, comment about specific places, connect with friends and find the ones who are near a specific location. To take advantage of the information that users share in these networks, Location-based Recommender Systems (LBRSs) generate suggestions based on the application of different recommendation techniques, being collaborative filtering (CF) one of the most traditional ones. In this article we analyze different strategies for selecting neighbors in the classic CF approach, considering information contained in the users’ social network, common visits, and place of residence as influential factors. The proposed approaches were evaluated using data from a popular location based social network, showing improvements over the classic collaborative filtering approach.Fil: Rios, Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto Superior de Ingeniería del Software. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto Superior de Ingeniería del Software; ArgentinaFil: Schiaffino, Silvia Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto Superior de Ingeniería del Software. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto Superior de Ingeniería del Software; ArgentinaFil: Godoy, Daniela Lis. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Instituto Superior de Ingeniería del Software. Universidad Nacional del Centro de la Provincia de Buenos Aires. Instituto Superior de Ingeniería del Software; Argentin

Information Retrieval Models for Contact Recommendation in Social Networks

The fast growth and development of online social networks has posed new challenges for information retrieval and, as a particular case, recommender systems. A particularly compelling problem in this context is recommending network edges, that is, automatically predicting people that a given user may wish or benefit from connecting to in the network. This task has interesting particularities compared to more traditional recommendation domains, a salient one being that recommended items belong to the same space as the users they are recommended to. In this paper, we investigate the connection between the contact recommendation and the text retrieval tasks. Specifically, we research the adaptation of IR models for recommending contacts in social networks. We report experiments over data downloaded from Twitter where we observe that IR models, particularly BM25, are competitive compared to state-of-the art contact recommendation methods. We further find that IR models have additional advantages in computational efficiency, and allow for fast incremental updates of recommendations as the network grows