A Framework for the Selection of Plant Growth-Promoting Rhizobacteria Based on Bacterial Competence Mechanisms.

The use of plant growth-promoting rhizobacteria (PGPR) is increasingly meaningful for the development of more environmentally friendly agricultural practices. However, often the PGPR strains selected in the laboratory fail to confer the expected beneficial effects when evaluated in plant experiments. Insufficient rhizosphere colonization is pointed out as one of the causes. With the aim of minimizing this inconsistency, we propose that besides studying plant growth promotion traits (PGP), the screening strategy should include evaluation of the microbial phenotypes required for colonization and persistence. As a model, we carried out this strategy in three Rhizobium sp. strains that showed phosphorus solubilization ability and production of siderophores. All strains displayed colonization phenotypes like surface spreading, resistance to hydrogen peroxide, and formed biofilms. Regarding their ability to persist, biofilm formation was observed to be influenced by pH and the phosphorus nutrient provided in the growth media. Differences in the competence of the strains to use several carbon substrates were also detected. As part of our framework, we compared the phenotypic characteristics of the strains in a quantitative manner. The data analysis was integrated using a multicriteria decision analysis (MCDA). All our results were scored, weighted, and grouped as relevant for PGP, colonization, or persistence. MCDA demonstrated that, when the phenotypes related to PGP and colonization are weighted over those for persistence, strain B02 performs better than the other two Rhizobium sp. strains. The use of our framework could assist the selection of more competent strains to be tested in greenhouse and field trials.IMPORTANCE Numerous plant growth-promoting rhizobacteria (PGPR) have been inoculated into the soil with the aim of improving the supply of nutrients to crop plants and decreasing the requirement of chemical fertilizers. However, sometimes these microbes fail to competitively colonize the plant roots and rhizosphere. Hence, the plant growth promotion effect is not observed. Here, we describe a new screening strategy aiming at the selection of more competent PGPR. We evaluated bacterial phenotypes related to plant growth promotion, colonization, and persistence. Our results demonstrated that despite the fact that our Rhizobium sp. strains successfully solubilized phosphorus and produced siderophores, their abilities to spread over surfaces, resist hydrogen peroxide, and form biofilms varied. Additionally, a multicriteria decision analysis was used to analyze the data that originated from bacterial physiological characterizations. This analysis allowed us to innovatively evaluate each strain as a whole and compare the performances of the strains under hypothetical scenarios of bacterial-trait requirements.

Métodos de identificación polifásica aplicados a la búsqueda de microorganismos con potencial industrial / Polyphasic identification methods applied in searching for microorganisms with industrial potential

Introducción: La bioprospección de metabolitos de interés antropogénico emplea métodos de recolección de microorganismos en ecosistemas extremófilos o endémicos. La microbiota aislada en estos lugares puede o no incluir microorganismos patógenos. Es imprescindible un enfoque interdisciplinario que permita abordar la búsqueda de las especies de interés mientras se preserva la buena salud de los investigadores. Objetivo: Identificar molecular, bioquímica y morfológicamente microorganismos patógenos humanos en cepas celulolíticas de importancia industrial almacenadas en el banco de cepas del Laboratorio de Investigación de la Facultad de Ingeniería Química de la Universidad Central del Ecuador, procedentes del Yasuní, la Antártida y Balzapamba. Métodos: Se realizó un estudio de bioprospección de bacterias celulolíticas empleando técnicas de microbiología ambiental. Se evaluaron las características morfológicas mediante tinciones, como por ejemplo Gram. Además, se realizaron pruebas bioquímicas y antibiogramas para bacterias Gram-negativas y Gram-positivas. Las pruebas moleculares utilizaron extracción de ADN bacteriano para la secuenciación Sanger del gen 16S. Resultados: Se encontraron las especies Klebsiella pneumoniae (Y2 y Y3r) y Nocardia asteroides (Y1 y Y3p) en las muestras de material lignocelulósico recolectadas en Yasuní, mientras que las especies aisladas en la Antártida y en Balzapamba corresponden a Bacillus subtillis. Conclusiones: Se identificaron cepas pertenecientes a diferentes géneros bacterianos. Las bacterias del género Klebsiella, en las muestras colectadas en Yasuní, podrían tener un potencial patógeno. Eso se puede corroborar con técnicas de genotipificación. Por lo tanto, puede existir riesgo para los seres humanos que realizan bioprospección en ese ecosistema y se deben tomar medidas de bioseguridad.

Abstract Background: The bioprospection of metabolites of anthropogenic interests employs methods of collecting microorganisms in extremophile or endemic ecosystems. The microbiota isolated in these places may or may not include pathogenic microorganisms. Therefore, an interdisciplinary approach is essential to address the search of the species of interest while the good health of the researchers is preserved. Objective: To identify in molecular, biochemical and morphologically ways some human pathogenic microorganisms in cellulolytic strains of industrial importance stored in the strain bank of the Research Laboratory of the Faculty of Chemical Engineering at the Central University of Ecuador, from Yasuní, Antarctic and Balzapamba. Methods: IA bioprospecting study of cellulolytic bacteria was performed using environmental microbiology techniques. Morphological characteristics were assessed by Gram staining. In addition, biochemical tests and antibiograms were performed for Gram-negative and Gram-positive bacteria. The molecular tests used extraction of bacterial ADN for 16S gene Sanger sequencing. Results: The species Klebsiella pneumoniae (Y2 and Y3r) and Nocardia asteroides (Y1 and Y3p) were found in samples of lignocellulosic material collected in Yasuni, while the isolated species in Antarctica and Balzapamba correspond to Bacillus subtillis. Conclusions: Strains belonging to different bacterial genera were identified. The bacteria of the genus Klebsiella from the samples collected in Yasuní could have a potential pathogen. This can be corroborated with genotyping techniques. Therefore, there could be a risk to humans who perform bioprospecting in that ecosystem and biosecurity measures should be taken.

Aspergillus sclerotiorum: riesgo para la herencia cultural y la salud / Aspergillus sclerotiorum: a risk to cultural heritage and health Abstract / Aspergillus sclerotiorum: risco para a herança cultural e para a saúde

A partir de una mancha de enmohecido de un libro del Archivo "Coronado" con valor patrimonial, se obtuvo una cepa fúngica mediante aislamiento en medio de cultivo micológico. La cepa fué Aspergillus sclerotiorum y se identificó por secuenciación de ADN ribosomal. Se evaluó y confirmó su capacidad deteriorante sobre el papel, al determinar cualitativamente las actividades enzimáticas celulolítica, proteolítica y amilolítica, así como la producción de pigmentos y ácidos. Se evaluaron cuantitativamente sus actividades enzimáticas celulasa total sobre papel de filtro (FPasa) y &beta-endoglucanasa, FPasa y &beta-endoglucanasa; confirmando actividades bajas. Aunque su capacidad deteriorante es discreta, resulta ser amenza para la conservación del documento y potencialmente peligroso para la salud de las personas que consultan y archivan.

By performing a mycological culture, we isolated a fungal strain from a mold patch in a book of great heritage value from the "Coronado" archives. Ribosomal DNA sequencing identified the strain as Aspergillus sclerotiorum. By qualitatively determining its cellulolytic, proteolytic and amylolytic and enzymatic activities, as well as the production of pigments and acids, we confirmed its paper deteriorating abilities. Quantitatively, we evaluated its total cellulase enzyme activities on filter paper (FPase) and &beta-endoglucanase, and FPase and &beta-endoglucanase; confirming low activities. Although its deteriorating abilities are weak, it poses a threat to the preservation of the document and is a potential health hazard to the people who refer to and archive these books.

A partir de uma mancha de bolor de um livro do Arquivo "Coronado" com valor patrimonial, obteve-se uma cepa fúngica mediante isolamento em meio de cultura micologica. A cepa foi Aspergillus sclerotiorum e identificou-se por sequenciação de ADN ribossomal. Avaliou-se e confirmou-se a sua capacidade deteriorantesobre o papel, ao determinar qualitativamente as atividades enzimáticas celulósica, proteolitica e amiolitica, assim como a produção de epigmentos e ácidos. Avaliaram-se quantitativamente as suas atividades enzimáticas celulase toral sobre o papel de filtro (FPasa) e &beta-endoglucanasa, FPasa e &beta-endoglucanasa; confirmando atividades baixas. Apesar da sua capacidade deteriorante ser discreta, resulta ser ameaçante para a conservação do documento e potencialmente perigoso para a saúde das pessoas que consultam e arquivam.