In vitro activity of cefiderocol and other newly approved antimicrobials against multi-drug resistant Gram-negative pathogens recovered in intensive care units in Spain and Portugal.

OBJECTIVE: The antimicrobial resistance is a significant public health threat, particularly for healthcare-associated infections caused by carbapenem-resistant Gram-negative pathogens which are increasingly reported worldwide. The aim of this study was to provide data on the in vitro antimicrobial activity of cefiderocol and that of commercially available comparator antibiotics against a defined collection of recent clinical multi-drug resistant (MDR) microorganisms, including carbapenem resistant Gram-negative bacteria collected from different regions in Spain and Portugal. METHODS: A total of 477 clinical isolates of Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia were prospectively (n=265) and retrospectively (n=212) included (2016-2019). Susceptibility testing was performed using standard broad microdilution and results were interpreted using CLSI-2021 and EUCAST-2021 criteria. RESULTS: Overall, cefiderocol showed a good activity against Enterobacterales isolates, being 99.5% susceptible by CLSI and 94.5% by EUCAST criteria. It also demonstrated excellent activity against P. aeruginosa and S. maltophilia isolates, all being susceptible to this compound considering CLSI breakpoints. Regarding A. baumannii (n=64), only one isolate was resistant to cefiderocol. CONCLUSIONS: Our results are in agreement with other studies performed outside Spain and Portugal highlighting its excellent activity against MDR gram-negative bacteria. Cefiderocol is a therapeutic alternative to those available for the treatment of infections caused by these MDR bacteria.

In vitro development of imipenem/relebactam resistance in KPC-producing Klebsiella pneumoniae involves multiple mutations including OmpK36 disruption and KPC modification.

OBJECTIVES: In order to inform and anticipate potential strategies aimed at combating KPC-producing Klebsiella pneumoniae infections, we analysed imipenem/relebactam and ceftazidime/avibactam single-step mutant frequencies, resistance development trajectories, differentially selected resistance mechanisms and their associated fitness cost using four representative high-risk K. pneumoniae clones. METHODS: Mutant frequencies and mutant preventive concentrations were determined using agar plates containing incremental concentrations of ß-lactam/ß-lactamase inhibitor. Resistance dynamics were determined through incubation for 7 days in 10 mL MH tubes containing incremental concentrations of each antibiotic combination up to their 64 × baseline MIC. Two colonies per strain from each experiment were characterized by antimicrobial susceptibility testing, whole genome sequencing and competitive growth assays (to determine in vitro fitness). KPC variants associated with imipenem/relebactam resistance were characterized by cloning and biochemical experiments, atomic models and molecular dynamics simulation studies. RESULTS: Imipenem/relebactam prevented the emergence of single-step resistance mutants at lower concentrations than ceftazidime/avibactam. In three of the four strains evaluated, imipenem/relebactam resistance development emerged more rapidly, and in the ST512/KPC-3 clone reached higher levels compared to baseline MICs than for ceftazidime/avibactam. Lineages evolved in the presence of ceftazidime/avibactam showed KPC substitutions associated with high-level ceftazidime/avibactam resistance, increased imipenem/relebactam susceptibility and low fitness costs. Lineages that evolved in the presence of imipenem/relebactam showed OmpK36 disruption, KPC modifications (S106L, N132S, L167R) and strain-specific substitutions associated with imipenem/relebactam resistance and high fitness costs. Imipenem/relebactam-selected KPC derivatives demonstrated enhanced relebactam resistance through important changes affecting relebactam recognition and positioning. CONCLUSIONS: Our findings anticipate potential resistance mechanisms affecting imipenem/relebactam during treatment of KPC-producing K. pneumoniae infections.

Bacterial inoculation of Quercus pyrenaica trees alters co-occurrence patterns but not the composition of the rhizosphere bacteriome in wild conditions.

Quercus pyrenaica is a woody species of high landscape value, however, its forests show an advanced state of degradation in the Iberian Peninsula. Afforestation typically has low success, thus, it is necessary to improve the fitness of oaks plantlets to be transplanted, for instance, by inoculating beneficial microorganisms. In adding microorganisms to ecosystems, there must be balanced efficacy with potential effects on native microbial communities. We addressed changes in diversity, richness, composition and co-occurrence networks of prokaryotic communities in the rhizosphere of inoculated and control trees outplanted to three different sites located in the Sierra Nevada National and Natural Park (Spain). After 18 months in wild conditions, we did not detect changes due to the inoculation in the richness, diversity and structure in none of the sites. However, we observed an increase in the complexity of the co-occurrence networks in two experimental areas. Modularization of the networks changed as a result of the inoculation, although the sense of the change depended on the site. Although it was impossible to unravel the effect of bacterial inoculation, our results highlighted that inoculation alters the association of rhizosphere bacteria without entailing other changes, so networks should be analysed prior to inoculating the plantlets.

Sketched reference databases for genome-based taxonomy and comparative genomics.

The analysis of curated genomic, metagenomic and proteomic data is of paramount importance in the fields of biology, medicine, education, and bioinformatics. Although this type of data is usually hosted in raw format on free international repositories, the full access requires lots of computing power and large storage disk space for the domestic user. The purpose of the study is to offer a comprehensive set of microbial genomic and proteomic reference databases in an accessible and easy-to-use form to the scientific community and demonstrate its advantages and usefulness. Also, we present a case study on the applicability of the sketched data, for the determination of overall genomic coherence between two members of the Brucellacea family, which suggests they belong to the same genomospecies that remain as discrete ecotypes. A representative set of genomes, proteomes (from type material), and metagenomes were directly collected from the NCBI Assembly database and Genome Taxonomy Database (GTDB), associated with the major groups of Bacteria, Archaea, Virus, and Fungi. Sketched databases were subsequently created and stored on handy reduced representations by using the MinHash algorithm implemented in Mash software. The obtained dataset contains more than 133 GB of space disk reduced to 883.25 MB and represents 125,110 genomics/proteomic records from eight informative contexts, which have been prefiltered to make them accessible, usable, and user-friendly with limited computational resources. Potential uses of these sketched databases are discussed, including but not limited to microbial species delimitation, estimation of genomic distances and genomic novelties, paired comparisons between proteomes, genomes, and metagenomes; phylogenetic neighbor's exploration and selection, among others.

The Maser Emitting Structure and Time Variability of the SIS Lines J = 14 - 13 and 15 - 14 in IRC+10216.

We present new high angular resolution interferometer observations of the υ = 0 J = 14 - 13 and 15 - 14 SiS lines towards IRC+10216, carried out with CARMA and ALMA. The maps, with angular resolutions of ≃0⋅″25and0⋅″55, reveal (1) an extended, roughly uniform, and weak emission with a size of ≃0⋅″5, (2) a component elongated approximately along the East-West direction peaking at ≃0⋅″13and0⋅″17 at both sides of the central star, and (3) two blue- and red-shifted compact components peaking around 0⋅″07 to the NW of the star. We have modeled the emission with a 3D radiation transfer code finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20R⋆ from the central star, in addition to a thin shell-like maser structure at ≃ 13R⋆ are required to explain the observations. This maser emitting set of structures accounts for 75% of the total emission while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission and the rest from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and 29SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation while other components show a mild variability. This monitoring evidences a significant phase lag of ≃ 0.2 between the maser and NIR light-curves.

Evaluación del conocimiento y de las habilidades para el uso de un Desfibrilador Externo Automatizado (DEA) por estudiantes universitarios. Un diseño cuasiexperimental / Assessment of knowledge and skills in using an Automated External Defibrillator (AED) by university students. A quasi-experimental study

Objetivo: Evaluar la capacidad del personal lego (estudiantes universitarios) para usar un desfibrilador externo automatizado (DEA). Diseño: Estudio cuasiexperimental de medidas repetidas de muestreo no probabilístico con grupo control. Ámbito: Estudiantes de formación de profesorado de la Universidad de Santiago de Compostela. Participantes: La muestra estuvo compuesta por 129 sujetos, 69% mujeres y 31% hombres, de entre 19 y 47 años (media 23,2 ± 4,7), cuyo criterio de inclusión fue el no tener conocimientos previos sobre DEA. Intervenciones: Se tomaron los tiempos empleados en aplicar una descarga sobre un maniquí con DEA sin formación (T0); tras una explicación teórico-práctica inferior a 1 minuto (T1) y tras 6 meses del proceso formativo (T2). Variables de interés principales: La variable de resultado principal fue el tiempo empleado en aplicar una descarga. Se definió la variable «efecto de mejora» mediante la diferencia absoluta de tiempo entre T1 y T0, y la variable «efecto de grado de olvido» como la diferencia absoluta entre T1 y T2. Resultados: Las medias de tiempos fueron: T0 = 67,7 s; T1 = 44,2 s; T2 = 45,9 s. Se redujo el tiempo para realizar una descarga tras la explicación formativa (T1 < T0) (−23,4 s; p < 0,001). El T2 es inferior a T0 (−21,8 s; p < 0,001), pero mayor que T1 (1,6 s; p = 0,002). El efecto de mejora fue significativo (p < 0,001), al igual que el grado de olvido (p = 0,002). Conclusiones: Se demostró el fácil manejo del DEA, ya que personas sin formación fueron capaces de aplicar una descarga. El tiempo de administración de descarga se redujo tras una pequeña formación. Este tiempo apenas aumentó pasados 6 meses (AU)

Aim: To evaluate layperson (university student) ability to use an automated external defibrillator (AED). Design: A repeated measures quasi-experimental study with non-probabilistic sampling and a control group was carried out. Scope: Teacher training degree students at the University of Santiago de Compostela (Spain). Participants: The sample consisted of 129 subjects (69% women and 31% men), between 19-47 years of age (mean 23.2 ± 4.7 years). As inclusion criterion, the subjects were required to have no previous knowledge of AED. Interventions: Times to apply defibrillation with an AED to a mannequin were recorded untrained (T0), after a theoretical and practice explanation lasting less than one minute (T1), and 6 months after the training process (T2). Main variables of interest: The primary endpoint was the time taken to deliver a defibrillation discharge. The «improvement effect» variable was defined by the absolute time difference between T1 and T0, while the «degree of forgetfulness effect» variable was defined as the absolute difference between T1 and T2. Results: The mean times were T0 = 67.7 s; T1 = 44.2 s; T2 = 45.9 s. The time to apply defibrillation was reduced after explanation training (T1 < T0) (−23.4 s; P < .001). T2 proved shorter than T0 (−21.8 s; P < .001) but longer than T1 (1.6 s; P = .002). The improvement effect was significant (P < .001), in the same way as the degree of forgetfulness (P = .002). Conclusions: Easy handling of AED was demonstrated, since untrained people were able to deliver a discharge. Defibrillation time was reduced after brief training. This time barely increased after 6 months (AU)

Clinical utility of partially hydrolyzed guar gum: review of evidence and experience / Utilidad en la clínica de la goma guar parcialmente hidrolizada: revisión de la evidencia y experiencia

Introduction: Dietary fiber is an important component of human diet. Since each fiber type has specific metabolic and gastrointestinal function effects, in each specific pathology we will have to choose the optimum type of fiber, considering its chemical, physical and physiological properties. Objective:to put partially hydrolyzed guar gum in its place in the complex framework of dietary fiber, to review its physicochemical properties and possible mechanisms of action; as well as its potential usefulness in different clinical situations in adult patients. Methods: non-systematic review in Medline. Results: Partially hydrolyzed guar gum (PHGG) is obtained from a partial enzymatic hydrolysis of guar gum by the enzyme ß-endo-mannanase. It is a soluble, highly fermentable fiber with low viscosity. The fermentation of GGPH in colon produces short chain fatty acids, implicated in the main pathophysiological mechanisms responsible for their clinical effects. Its use in enteral nutrition associated diarrhea is supported by several studies and by the recommendations of scientific societies such as the European Society for Clinical Nutrition and Metabolism and the American Society for Parenteral and Enteral Nutrition. The usefulness of GGPH has been studied in many other clinical situations, such as diabetes, hypercholesterolemia, bacterial overgrowth, etc. with promising results. Conclusions: GGPH is useful in the management of enteral nutrition associated diarrhea. In other clinical situations, more quality studies would be necessary in order to make concrete recommendations.

Introducción: la fibra dietética es un componente importante de la dieta humana. Cada tipo de fibra tiene efectos específicos a nivel metabólico y en el funcionamiento gastrointestinal, por lo que en cada patología concreta habremos de elegir la fibra óptima teniendo en cuenta sus propiedades químicas, físicas y fisiológicas. Objetivo: encuadrar la goma guar parcialmente hidrolizada en su lugar en el complejo marco de la fibra dietética, revisar sus propiedades físico-químicas y posibles mecanismos de acción; así como su potencial utilidad en distintas situaciones clínicas en pacientes adultos. Métodos: revisión no sistemática en Medline. Resultados: la goma guar parcialmente hidrolizada (GGPH) se obtiene a partir de una hidrólisis enzimática parcial de la goma guar mediantela enzima ß-endo-mananasa. Se trata de una fibra soluble, altamente fermentable y de baja viscosidad. La fermentación de la GGPH a nivel colónico produce ácidos grasos de cadena corta, implicados en los principales mecanismos fisiopatólogicos responsables de sus efectos a nivel clínico. Su uso en la diarrea asociada a la nutrición enteral está avalada por diversos estudios y por la recomendaciones de sociedades científicas como la European Society for Clinical Nutrition and Metabolism y la American Society for Parenteral and Enteral Nutrition. Se ha estudiado la utilidad de la GGPH en otras muchas situaciones clínicas, como diabetes, hipercolesterolemia, sobrecrecimiento bacteriano, etc. con resultados prometedores. Conclusiones: la GGPH es útil en el manejo de la diarrea asociada a nutrición enteral. Respecto a otras situaciones clínicas, serían necesarios más estudios de calidad para poder hacer recomendaciones concretas.

Arbuscular mycorrhizal fungi inoculation mediated changes in rhizosphere bacterial community structure while promoting revegetation in a semiarid ecosystem.

The main goal of this study was to assess the effect of the inoculation of four autochthonous shrub species with the arbuscular mycorrhizal (AM) fungus Rhizophagus intraradices on the rhizosphere bacterial community and to ascertain whether such an effect is dependent on the host plant species. Additionally, analysis of rhizosphere soil chemical and biochemical properties was performed to find relationships between them and the rhizosphere bacterial communities. Non-metric multidimensional scaling analysis and subsequent permutational multivariate analysis of variance revealed differences in bacterial community composition and structure between non-inoculated and inoculated rhizospheres. Moreover, an influence of the plant species was observed. Different bacterial groups were found to be indicator taxonomic groups of non-inoculated and inoculated rhizospheres, Gemmatimonadetes and Anaerolineaceae, respectively, being the most notable indicators. As shown by distance based redundancy analysis, the shifts in bacterial community composition and structure mediated by the inoculation with the AM fungus were mainly related to changes in plant nutrients and growth parameters, such as the shoot phosphorus content. Our findings suggest that the AM fungal inoculum was able to modify the rhizosphere bacterial community assemblage while improving the host plant performance.

Assessment of knowledge and skills in using an Automated External Defibrillator (AED) by university students. A quasi-experimental study. / Evaluación del conocimiento y de las habilidades para el uso de un Desfibrilador Externo Automatizado (DEA) por estudiantes universitarios. Un diseño cuasiexperimental.

AIM: To evaluate layperson (university student) ability to use an automated external defibrillator (AED). DESIGN: A repeated measures quasi-experimental study with non-probabilistic sampling and a control group was carried out. SCOPE: Teacher training degree students at the University of Santiago de Compostela (Spain). PARTICIPANTS: The sample consisted of 129 subjects (69% women and 31% men), between 19-47 years of age (mean 23.2±4.7 years). As inclusion criterion, the subjects were required to have no previous knowledge of AED. INTERVENTIONS: Times to apply defibrillation with an AED to a mannequin were recorded untrained (T0), after a theoretical and practice explanation lasting less than one minute (T1), and 6 months after the training process (T2). MAIN VARIABLES OF INTEREST: The primary endpoint was the time taken to deliver a defibrillation discharge. The "improvement effect" variable was defined by the absolute time difference between T1 and T0, while the "degree of forgetfulness effect" variable was defined as the absolute difference between T1 and T2. RESULTS: The mean times were T0=67.7s; T1=44.2s; T2=45.9s. The time to apply defibrillation was reduced after explanation training (T1

Kinetic analysis of manure pyrolysis and combustion processes.

Due to the depletion of fossil fuel reserves and the environmental issues derived from their use, biomass seems to be an excellent source of renewable energy. In this work, the kinetics of the pyrolysis and combustion of three different biomass waste samples (two dairy manure samples before (Pre) and after (Dig R) anaerobic digestion and one swine manure sample (SW)) was studied by means of thermogravimetric analysis. In this work, three iso-conversional methods (Friedman, Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) were compared with the Coats-Redfern method. The Ea values of devolatilization stages were in the range of 152-170kJ/mol, 148-178kJ/mol and 156-209kJ/mol for samples Pre, Dig R and SW, respectively. Concerning combustion process, char oxidation stages showed lower Ea values than that obtained for the combustion devolatilization stage, being in the range of 140-175kJ/mol, 178-199kJ/mol and 122-144kJ/mol for samples Pre, Dig R and SW, respectively. These results were practically the same for samples Pre and Dig R, which means that the kinetics of the thermochemical processes were not affected by anaerobic digestion. Finally, the distributed activation energy model (DAEM) and the pseudo-multi component stage model (PMSM) were applied to predict the weight loss curves of pyrolysis and combustion. DAEM was the best model that fitted the experimental data.

Life cycle assessment of swine and dairy manure: pyrolysis and combustion processes.

The valorization of three different manure samples via pyrolysis and combustion processes was evaluated. Dairy manure (sample Pre) was biologically pretreated by anaerobic digestion (sample Dig R) whereas swine manure (sample SW) was pretreated by a biodrying process. Thermal behavior of manure samples were studied by means of thermogravimetric analysis coupled with mass spectrometry (TGA-MS). These processes could be divided into four general stages: dehydration, devolatilization, char transformation (oxidation for combustion) and inorganic matter decomposition. The main differences observed among the samples were attributed to their different composition and pretreatment. The economic feasibility, energetic and environmental impacts of pyrolysis and combustion technologies for dairy samples were carried out by means of life cycle assessment (LCA) methodology. Four different scenarios were analyzed. The economic feasibility of the pyrolysis process was demonstrated, being sample Dig R the best environmental option. However, the combustion of sample Pre was the best energetic option.

The abundance of 28Si32S, 29Si32S, 28Si34S, and 30Si32S in the inner layers of the envelope of IRC+10216.

We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC+10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of 28Si32S, 26 of 29Si32S, 20 of 28Si34S, and 15 of 30Si32S in the frequency range 720 - 790 cm-1. These lines belong to bands v = 1 - 0, 2 - 1, 3 - 2, 4-3, and 5-4, and involve rotational levels with Jlow ≲ 90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust. The observed lines trace the envelope at distances to the star ≲ 35R⋆(≃ 0″.7). The fits are compatible with an expansion velocity of 1+2.5(r/R⋆ -1) km s-1 between 1 and 5R⋆, 11 km s-1 between 5 and 20R⋆, and 14.5 km s-1 outwards. The derived abundance profile of 28Si32S with respect to H2 is 4.9 × 10-6 between the stellar photosphere and 5R⋆, decreasing linearly down to 1.6 × 10-6 at 20R⋆ and to 1.3 × 10-6 at 50R⋆. 28Si32S seems to be rotationally under LTE in the region of the envelope probed with our observations and vibrationally out of LTE in most of it. There is a red-shifted emission excess in the 28Si32S lines of band v = 1 - 0 that cannot be found in the lines of bands v = 2 - 1, 3 - 2, 4 - 3, and 5 - 4. This excess could be explained by an enhancement of the vibrational temperature around 20R⋆ behind the star. The derived isotopic ratios 28Si/29Si, and 32S/34S are 17 and 14, compatible with previous estimates.

[Gout, revisited]. / La goutte, revisitée.

In recent decades, gout became the most common inflammatory arthritis and one in which pathogenesis and risk factors are best understood. One of the treatment objectives in current guidelines is "cure". However, audits show that minority of patients with gout receive adequate advice and treatment. Doctors often focus on managing acute attacks rather than viewing gout as a chronic progressive crystal deposition disease. Accordingly, urate-lowering treatment is underprescribed and often underdosed. The recent introduction of a panel of new treatments of gout and a better understanding of epidemiologic factors (such as the fructose) may improve management of this easily diagnosed and curable form of potentially severe arthritis, worsening probably the cardiovascular prognostic.

[Ultrasonography and rheumatology]. / L'échographie dans la pratique rhumatologique.

Muskuloskeletal ultrasound has been incorporated by rheumatologist to the clinical practice over the past decade. The technical improvements of the devices allowed the production of high quality images contributing to better identification of joint inflammation and structural damage. In this review, we highlight the applications of ultrasound in the study of different rheumatic conditions.

Thermogravimetric-mass spectrometric analysis on combustion of lignocellulosic biomass.

Combustion characteristics of biomass main components and three lignocellulosic biomass (fir wood, eucalyptus wood and pine bark) were investigated by thermogravimetric analysis coupled with mass spectrometry. The combustion of biomass was divided into two main steps, devolatilization and char oxidation stage. Heating rate effect was also studied. Generally, the higher the heating rate, the higher the decomposition temperature. Furthermore, the weight loss rate decreased due to particle temperature gradients. Combustion kinetics were studied. Models based on reaction order (Oi), nucleation (Ni) and diffusion (Di) achieved the best fitting to the experimental data. Cellulose oxidation presented the highest activation energies. CO, CO2 and H2O were the main components evolved from combustion. Additionally, light hydrocarbons (CH4 and C2H5) were also present. Finally, nitrogen compounds were in a higher proportion than sulfur compounds being released as primary amines and NOx.

Refeeding syndrome.

Refeeding syndrome is a complex syndrome that occurs as a result of reintroducing nutrition (oral, enteral or parenteral) to patients who are starved or malnourished. Patients can develop fluid-balance abnormalities, electrolyte disorders (hypophosphataemia, hypokalaemia and hypomagnesaemia), abnormal glucose metabolism and certain vitamin deficiencies. Refeeding syndrome encompasses abnormalities affecting multiple organ systems, including neurological, pulmonary, cardiac, neuromuscular and haematological functions. Pathogenic mechanisms involved in the refeeding syndrome and clinical manifestations have been reviewed. We provide suggestions for the prevention and treatment of refeeding syndrome. The most important steps are to identify patients at risk, reintroduce nutrition cautiously and correct electrolyte and vitamin deficiencies properly.

El tortícolis como manifestación inicial de un tumor de fosa posterior: el caso de una niña con astrocitoma pilocítico / Torticolis as an initial sign of posterior fossa tumor: case of child with pilocytic astrocytoma

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Low back pain as presenting manifestation of giant cell arteritis associated to abdominal aortitis.

Giant cell arteritis (GCA) is the most common vasculitis in Western countries in individuals over the age of 50. The diagnosis is relatively straightforward when typical features, such as headache, jaw claudication or other ischemic complications are present. Although atypical presentations of GCA have been described, herein we report for first time low back pain as the presenting manifestation of this vasculitis. We also emphasize the importance of considering the use of positron emission tomography (PET) in the evaluation of GCA patients presenting without "overt" cranial ischemic manifestations.

Rhizosphere-bacterial community in Eperua falcata (Caesalpiniaceae) a putative nitrogen-fixing tree from French Guiana rainforest.

The rainforest of French Guiana is still largely unaffected by human activity. Various pristine sites like the Paracou Research Station are devoted to study this tropical ecosystem. We used culture-independent techniques, like polymerase chain reaction-temperature gradient gel electrophoresis, and construction of clone libraries of partial 16S rRNA and nifH genes, to analyze the composition of the bacterial community in the rhizosphere of mature trees of Eperua falcata and Dicorynia guianensis, both species within the Caesalpiniaceae family. E. falcata is one of the more abundant pioneer tree species in this ecosystem and so far, no root nodules have ever been found. However, its nitrogen-fixing status is regarded as "uncertain", whereas D. guianensis is clearly considered a non-nitrogen-fixing plant. The rhizospheres of these mature trees contain specific bacterial communities, including several currently found uncultured microorganisms. In these communities, there are putative nitrogen-fixing bacteria specifically associated to each tree: D. guianensis harbors several Rhizobium spp. and E. falcata members of the genera Burkholderia and Bradyrhizobium. In addition, nifH sequences in the rhizosphere of the latter tree were very diverse. Retrieved sequences were related to bacteria belonging to the alpha-, beta-, and gamma-Proteobacteria in the E. falcata rhizoplane, whereas only two sequences related to gamma-Proteobacteria were found in D. guianensis. Differences in the bacterial communities and the abundance and diversity of nifH sequences in E. falcata rhizosphere suggest that this tree could obtain nitrogen through a nonnodulating bacterial interaction.