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12 páginas, 5 tablas, 1 figura, The legume nodules are a rich source not only of rhizobia but also of endophytic bacteria exhibiting plant growth-promoting mechanisms with potential as plant biostimulants. In this work we analyzed the genomes of Phyllobacterium endophyticum PEPV15 and Rhizobium laguerreae PEPV16 strains, both isolated from Phaseolus vulgaris nodules. In silico analysis showed that the genomes of these two strains contain genes related to N-acyl-homoserine lactone (AHL) and cellulose biosynthesis, involved in quorum sensing and biofilm formation, which are essential for plant colonization. Several genes involved in plant growth promotion such as those related to phosphate solubilization, indole acetic acid production, siderophore biosynthesis and nitrogen fixation were also located in both genomes. When strains PEPV15 and PEPV16 were inoculated in lettuce and carrot in field assays, we found that both significantly increased the yield of lettuce shoots and carrot roots by more than 20% and 10%, respectively. The results of this work confirmed that the genome mining of genes involved in plant colonization and growth promotion is a good strategy for predicting the potential of bacterial strains as crops inoculants, opening new horizons for the selection of bacterial strains with which to design new, effective bacteria-based plant biostimulants., This work was supported by JCyL (Junta de Castilla y León, Spanish Regional government) grant SA183A11-2 to R.R. J.D.F.-F are granted with a FEMS grant FEMS-RG-2016-0213

Two slow-growing strains, AMBPC1010T and AMBPC1011, were isolated from nodules of Cajanus cajan in the Dominican Republic. 16S rRNA gene analysis placed these strains within the genus Bradyrhizobium , being phylogenetically equidistant to several species of this genus. Analysis of the recA and atpD genes showed that the strains isolated belong to a cluster containing the strains Bradyrhizobium ottawaense OO99T, ‘ Bradyrhizobium americanum' CMVU44 and Bradyrhizobium daqingense CCBAU 15774T, and presented similarity values lower than 96 % for both genes with respect to the strains nodulating C. cajan. DNA–DNA hybridization analysis showed averages of 36, 40 and 39 % relatedness with respect to the representative strains of Bradyrhizobium ottawaense , ‘ Bradyrhizobium americanum' and Bradyrhizobium daqingense , respectively. Phenotypic characteristics also differed from those of the most closely related species of the genus Bradyrhizobium . Therefore, based on the data obtained in this study, we propose to classify the strains AMBPC1010T (=LMG 29967T=CECT 9227T) and AMBPC1011 into a novel species named Bradyrhizobium cajani sp. nov.

Legume nodules harbour two types of bacteria, the rhizobia, responsible for their formation, and other endophytic bacteria whose role in the nodule is still poorly known. These bacteria constitute the nodule microbiome from which the rhizobia have been widely studied for decades, whereas the nodule endophytes have been started to be studied in the last years. These studies showed a more complex bacterial composition than previously thought, including bacteria from very different phylogenetic groups. Unlike other plant microbiomes, which have been widely studied by metagenomic techniques, the nodule microbiomes have been basically studied by culture-dependent methods because the main objective of the legume nodule studies is the selection of plant growth-promoting bacteria to be used in agronomic practices in a sustainable agriculture context. In this chapter we revise the groups of bacteria found to date in legume nodules that present in vitro mechanisms of plant growth promotion, with special emphasis in those that are able to promote the plant growth in plant assays.

Black sigatoka caused by Mycosphaerella fijiensis (Morelet) is one of the main diseases affecting banana trees worldwide, resulting in a reduced fruit yield . Banana is a major export crop in many tropical and subtropical countries, and many farmers have decided to shift to an organic production system for produce that is destined for the international market. Induced systemic resistance (ISR) protects plants against disease-causing pathogens, and this mechanism can be triggered by some bacteria associated with plant roots. The inoculation of plant roots with bacteria able to induce systemic resistance in plants has been proposed for disease control in organic agriculture as an alternative to chemicals. Fifty-six nonpathogenic and endophytic strains isolated from roots of banana trees cv. Cavendish in organic systems from four regions of the Dominican Republic were the starting point for the present work. We used 26 of them to inoculate the root systems of banana plants, the leaves of which were inoculated with M. fijiensis inoculum, in order to analyse their effect on the control of black sigatoka under growth chamber conditions. The selection of the 26 strains to be tested in plants was based on the following plant growth-promoting (PGP) traits : production of siderophore (17 strains), production of IAA (two strains) and ACC deaminase activity (two strains); the remaining five showed low values for all of the PGP traits. The best controllers of sigatoka were five strains from the genus Bacillus (related to B. licheniformis, B. siamensis and B. subtilis ssp. inaquosorum) and one Rhizobium massiliae. With the six strains, the severity index (SI) of the plants coinoculated with the bacteria and the pathogen did not differ from the noninoculated control. The sigatoka control observed has been tentatively assigned to ISR phenomena, which is discussed in the chapter. The six selected strains could be used in the short term to control black sigatoka in organic banana production systems in the Dominican Republic.

Medicago strasseri, M. citrina, Colutea arborescens, and Dorycnium pentaphyllum are legume shrubs potentially useful for the revegetation of semiarid Mediterranean ecosystems and for animal grazing. As nodulation with specific rhizobia and/or mycorrhizal fungi, may become essential for the settlement and growth of legumes, the objective was to ascertain the specificity/promiscuity of the plant–rhizobia interaction, by detecting the occurrence of infective rhizobia in the soils to be revegetated and by cross inoculation tests. Native rhizobia for the target species, were isolated from nondisturbed native areas. The four species were inoculated with four semiarid soils located in central Spain, that we intend to revegetate. Specific rhizobia for M. strasseri and M. citrina were detected in three of the four soils. The soil that did not show infective rhizobia had received sewage-sludge from a waste-water treatment plant, and levels of heavy metals were high. None of the 4 soils had specific rhizobia for C. ...

Iron and zinc are necessary nutrients whose homeostasis is tightly controlled by members of the ferric uptake regulator (FUR) superfamily in the cyanobacterium Anabaena sp. PCC7120. Although the link between iron metabolism and oxidative stress management is well documented, little is known about the connection between zinc homeostasis and the oxidative stress response in cyanobacteria. Zinc homeostasis in Anabaena is controlled by Zur, also named FurB. When overexpressed in Escherichia coli, Zur (FurB) improved cell survival during oxidative stress. In order to investigate the possible correlation between Zur and the oxidative stress response in Anabaena, zur deletion and zur-overexpressing strains have been constructed, and the consequences of Zur imbalance evaluated. The lack of Zur increased sensitivity to hydrogen peroxide (H2 O2 ), whereas an excess of Zur enhanced oxidative stress resistance. Both mutants displayed pleiotropic phenotypes, including alterations on the filament surfaces observable by scanning electron microscopy, reduced content of endogenous H2 O2 and altered expression of sodA, catalases and several peroxiredoxins. Transcriptional and biochemical analyses unveiled that the appropriate level of Zur is required for proper control of the oxidative stress response and allowed us to identify major antioxidant enzymes as novel members of the Zur regulon.

Genista monspessulana and Genista linifolia are woody legumes with a high potential value for the rehabilitation of degraded soils , although field establishment of the plantlets in nonnative soils is very difficult because of the lack of specific rhizobial strains . In this work the rhizobia that nodulate the two species were tenta tively classified as a Bradyrhizobium sp . Only those soils with naturally occurring G. monspessulana or G. linifolia, now or in the past , had specific bradyrhizobia . Out of the six rhizobial strains analyzed , only Bradyrhizobium sp . ISLU21 , iso lated from Lupinus luteus, nodulated with the species studied . Out of the 11 legumes inoculated with the strains isolated from G. monspessulana and G. linifolia, only L. luteus produced infective nodules . In a field experiment , plants inocu lated with the specific bradyrhizobia isolates showed higher survival , growth rates , and N content than the noninoculated controls .

269 p. El trabajo general del trabajo fue desarrollar biofertilizantes para banano (Musa sp.)utilizando bacterias autóctonas en República Dominicana, donde este producto es muy importante para la economía tanto como cultivo de subsistencia como para la exportación. Para ello se aislaron, caracterizaron y evaluaron en planta, bacterias asociadas a raíces de banano (Musa acuminata AAA) cv. Cavendish, procedentes de zonas productoras en régimen ecológico en República Dominicana. El trabajo concluye que las bacterias promotoras del crecimiento vegetal (Plant Growth Promoting Rhizobacteria, PGPR) como fertilizantes y biocontroladores del hongo Sikota Negra (Mycosphaerella Fijiensis Morelet) son una alternativa válida a los abonos minerales y a los fitosanitarios en banano, pues los mismos son capaces de aumentar el rendimiento