Phosphorus Solubilizing and Mineralizing Bacillus spp. Contribute to Rice Growth Promotion Using Soil Amended with Rice Straw.

Rice (Oryza sativa L.) is a staple food for more than two billion people worldwide. Its cultivation demands large amounts of nutrients, particularly nitrogen and phosphorus (P). Consequently, low availability of these nutrients in the soil has led to the use of chemical fertilizers, generating increases in production costs and environmental damage. Soil host microorganisms known as plant growth-promoting rhizobacteria (PGPR) colonize the rhizosphere and facilitate the uptake of nutrients by the plants. In this study, rice seeds inoculated with PGPR were grown for 30 days in an inert substrate and fertilized with modified Hoagland nutrient solution with phosphate rock as a source of P. Treatments were repeated over time, obtaining five isolates which significantly increased plant length by up to 56% and dry weight of stems and roots up to 45% and 169% respectively relative to an uninoculated control. Selected strains showed in vitro tri-calcium phosphate solubilizing activity, mineralizing phytate activity, and phosphate release from rice straw (RS). Based on the above criteria, three isolates (IBUN-02755, -02,704 and -02,724) that contained ß propeller phytase (BPP) genes, were selected to evaluate their effect as PGPR in rice seedlings. These were planted in a soil amended with RS under greenhouse conditions. The results showed that selected Bacillus spp. strains significantly increased plant length and dry weight or increased plant phosphate uptake up to two times compared to an un-inoculated control. This suggests that selected strains may have a capacity as PGPR using RS as carbon and a P amendment.

MECANISMOS DE ACCIÓN DE Bacillus spp. (Bacillaceae) CONTRA MICROORGANISMOS FITOPÁTOGENOS DURANTE SU INTERACCIÓN CON PLANTAS / Mechanisms of action of Bacillus spp. (Bacillaceae) against phytopathogenic microorganisms during their interaction with plants

RESUMEN Algunos Bacillus spp. promotores de crecimiento vegetal son microorganismos reconocidos como agentes de control biológico que forman una estructura de resistencia denominada endospora, que les permite sobrevivir en ambientes hostiles y estar en casi todos los agroecosistemas. Estos microorganismos han sido reportados como alternativa al uso de agroquímicos. Sus mecanismos de acción se pueden dividir en: producción de compuestos antimicrobianos, como son péptidos de síntesis no ribosomal (NRPs) y policétidos (PKs); producción de hormonas, capacidad de colonización, formación de biopelículas y competencia por espacio y nutrientes; síntesis de enzimas líticas como quitinasas, glucanasas, protesasas y acil homoserin lactonasas (AHSL); producción de compuestos orgánicos volátiles (VOCs); e inducción de resistencia sistémica (ISR). Estos mecanismos han sido reportados en la literatura en diversos estudios, principalmente llevados a cabo a nivel in vitro. Sin embargo, son pocos los estudios que contemplan la interacción dentro del sistema tritrófico: planta - microorganismos patógenos - Bacillus sp. (agente biocontrolador), a nivel in vivo. Es importante destacar que la actividad biocontroladora de los Bacillus es diferente cuando se estudia bajo condiciones de laboratorio, las cuales están sesgadas para lograr la máxima expresión de los mecanismos de acción. Por otra parte, a nivel in vivo, la interacción con la planta y el patógeno juegan un papel fundamental en la expresión de dichos mecanismos de acción, siendo esta más cercana a la situación real de campo. Esta revisión se centra en los mecanismos de acción de los Bacillus promotores de crecimiento vegetal, expresados bajo la interacción con la planta y el patógeno.

ABSTRACT Some Bacillus spp. plant growth promoters are microorganisms recognized as biological control agents, which form a resistance structure called endospore, which allows them to survive in hostile environments and be in almost all agroecosystems. These microorganisms have been reported as an alternative to the use of agrochemicals. Its mechanisms of action can be divided into: production of antimicrobial compounds, such as non-ribosomal peptides (NRPs) and polyketides (PKs); hormone production, colonization capacity, biofilm formation and competition for space and nutrients; synthesis of lytic enzymes such as chitinases, glucanases, protesases and acyl homoserin lactonases (AHSL); production of volatile organic compounds (VOCs); and induction of systemic resistance (SRI). These mechanisms have been reported in the literature in several studies, mainly carried out in vitro. However, there are few studies that contemplate the interaction within the tritrophic system: plant - pathogenic microorganisms -Bacillus sp. (biocontrol agent), in vivo level. It is important to note that the Bacillus biocontrol activity is different when studied under laboratory conditions, which are biased to achieve maximum expression of the mechanisms of action. On the other hand, at the in vivo level, the interaction with the plant and the pathogen play a fundamental role in the expression of said mechanisms of action, being this closer to the real field situation. This review focuses on the mechanisms of action of the Bacillus promoters of plant growth, expressed under the interaction with the plant and the pathogen.

Seed-born Burkholderia glumae Infects Rice Seedling and Maintains Bacterial Population during Vegetative and Reproductive Growth Stage.

Rice world production is affected due to the growing impact of diseases such as bacterial panicle blight, produced by Burkholderia glumae. The pathogen-induced symptoms include seedling rot, grain rot and leaf-sheath browning in rice plants. It is currently recognized the entrance of this pathogen to the plant, from infected seeds and from environmental sources of the microorganism. However, it is still not fully elucidated the dynamics and permanence of the pathogen in the plant, from its entry until the development of disease symptoms in seedlings or panicles. In this work it was evaluated the infection of B. glumae rice plants, starting from inoculated seeds and substrates, and its subsequent monitoring after infection. Various organs of the plant during the vegetative stage and until the beginning of the reproductive stage, were evaluated. In both inoculation models, the bacteria was maintained in the plant as an endophyte between 1 × 101 and 1 × 105 cfu of B. glumae.g-1 of plant throughout the vegetative stage. An increase of bacterial population towards initiation of the panicle was observed, and in the maturity of the grain, an endophyte population was identified in the flag leaf at 1 × 106 cfu of B. glumae.g-1 fresh weight of rice plant, conducting towards the symptoms of bacterial panicle blight. The results found, suggest that B. glumae in rice plants developed from infected seeds or from the substrate, can colonize seedlings, establishing and maintaining a bacterial population over time, using rice plants as habitat to survive endophyticly until formation of bacterial panicle blight symptoms.

Manejo biológico del tamo de arroz bajo diferentes relaciones C:N empleando consorcios microbianos y promotores de crecimiento vegetal / Bio-based management of rice straw under different C:N ratios using microbial consortia and plant growth promoters

Resumen El tamo de arroz es uno de los residuos agrícolas lignocelulósicos más abundantes en el planeta, luego de los residuos producidos por los cultivos de maíz y trigo, con una producción mundial estimada de 1000 millones de toneladas según estadísticas de la FAO. En el contexto de la agricultura moderna es determinante lograr un manejo ambientalmente sostenible de este recurso mediante su incorporación al suelo, de tal forma que se logre el reciclaje de nutrientes, evitando la incorporación de patógenos al sistema y la inmovilización de elementos como el nitrógeno por la comunidad microbiana. El objetivo de este trabajo consistió en la evaluación de un inoculo microbiano mixto a partir de productos comerciales basados en hongos del género Trichoderma y bacterias aerobias formadoras de endosporas, con potencial degradador del tamo de arroz, así como el empleo de bacterias promotoras de crecimiento vegetal al momento de la siembra, que pudieran aprovechar los nutrientes del proceso de descomposición del tamo de arroz, potenciando su actividad biológica. Los tratamientos fueron evaluados bajo diferentes relaciones C:N del tamo de arroz que favorecieran el proceso de degradación, mediante la adición de nitrógeno inorgánico. Los resultados del trabajo permitieron identificar que la aplicación de una enmienda de nitrógeno a una relación C:N 35 más una dosis adicional de urea al momento de la siembra de las semillas de arroz, fue el tratamiento más adecuado para potenciar el efecto de los microorganismos e incrementar las variables agronómicas obtenidas mediante un esquema de fertilización convencional del cultivo.

Abstract Rice straw is one of the most abundant lignocellulosic agricultural residues on the world, after residues produced by maize and wheat crops, with an estimated global production of 1000 million tones according to FAO statistics. In the context of modern agriculture, it is essential to achieve an environmentally sustainable management of this resource, through the incorporation of rice straw into the soil, in order to achieve nutrient recycling avoiding the incorporation of pathogens into the system and the losses of nitrogen due to soil microbial biomass immobilization. In this context, the objective of this work consisted in the evaluation of a mixed microbial inoculum with degrading potential of rice straw from commercial products based on the fungus Trichoderma spp. and aerobic endospore forming bacteria. It was also used a plant growth promoting bacteria at the time of planting, in order to take advantage of nutrients released from RS decomposition and improve its biological activity. These microbial treatments, were evaluated at different concentrations of inorganic nitrogen amendments that allowed different levels of rice straw´s C:N ratio, favoring the degradation process. Overall results allowed to identify that the application of a nitrogen amendment to rice straw up to C:N 35, plus an additional dose of urea at the time of rice seeds planting, was the most adequate treatment to potentiate the effect of the microorganisms and to increase or maintain the agronomic variables obtained through a conventional fertilization management of the crop.

Prototipo de formulación a base de Rhodotorula mucilaginosa para el control de Botrytis cinerea en Rosas / Formulation prototype based on Rhodotorula mucilaginosa for the control of Botrytis cinerea in Roses

Los sistemas productivos de Rosas de corte para exportación poseen retos importantes debido a la presencia de diversos agentes fitopatógenos, siendo Botrytis cinerea uno de los más relevantes debido a su persistencia y número de hospederos alternativos. Los mercados internacionales son muy exigentes en el manejo ambientalmente sostenible de los cultivos, por lo que se ha hecho presión para la implementación de estrategias de control biológico de enfermedades. La levadura filosferica Rhodotorula mucilaginosa (Lv20) con potencial biocontrolador contra B. cinérea, fue empleada en este estudio con el objeto de generar un prototipo de formulación en base sólida con el fin de lograr una estabilidad de la actividad y viabilidad celular a través del tiempo. El empleo de mezclas de polímeros sintéticos y de origen natural permitió mantener la viabilidad de esta cepa durante 90 días a unos niveles de 1,90x10(9) células.mL-1 a una temperatura de 25°C en una formulación líquida. Así mismo, el prototipo de formulación, empleando manitol como agente nucleador en una formulación sólida de tipo granulada, logró una viabilidad celular de 1.2x10(8) células.gr-1 a los 90 días de almacenamiento a 4°C, logrando mantener una actividad biocontroladora igual a la cepa fresca sin formular o recién formulada. Estos resultados obtenidos permiten sugerir que los prototipos de formulación empleando como principio activo la levadura R. mucilaginosa, son una alternativa promisoria para el control de B. cinerea en la post cosecha de rosas variedad véndela.

Productive systems of cut roses for exportation, have important challenges due to the presence of various plant pathogens in such crops. Botrytis cinerea is one of the most important pathogen microorganism because of its persistence and number of alternative hosts plants. International markets are very demanding in terms of environmentally sustainable crop management, which has forced for the implementation of strategies for biological control of diseases. The phyllosphere yeast Rhodotorula mucilaginous (Lv20) with biocontrol potential against B. cinerea, was employed in this study in order to generate a solid prototype formulation to achieve both, the stability of its activity and cell viability over time. The use of the mix of synthetic and naturally occurring polymers allowed to maintain the viability of this strain for 90 days at 1,90x10(9) células.mL-1 at a 25 ° C in a liquid formulation. Likewise, the prototype formulation using mannitol as a nucleating agent in a granular solid formulation, allowed obtaining a cell viability of 1.2x10(8) células.gr-1 after 90 days of storage at 4 °C, maintaining a biocontrol activity equal to the fresh strain with or without formulation. These results allow us to suggest that the formulation prototypes using R. mucilaginous yeast, is a promising alternative for the control of B. cinerea in post-harvest management of roses.

Bacteria with Phosphate Solubilizing Capacity Alter Mycorrhizal Fungal Growth Both Inside and Outside the Root and in the Presence of Native Microbial Communities.

Arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing Pseudomonas bacteria (PSB) could potentially interact synergistically because PSB solubilize phosphate into a form that AMF can absorb and transport to the plant. However, very little is known about the interactions between these two groups of microorganisms and how they influence the growth of each other. We tested whether different strains of bacteria, that have the capacity to solubilize phosphate, are able to grow along AMF hyphae and differentially influence the growth of AMF both outside the roots of carrot in in vitro conditions and inside the roots of potato in the presence of a microbial community. We found strong effects of AMF on the growth of the different bacterial strains. Different bacterial strains also had very strong effects on the growth of AMF extraradical hyphae outside the roots of carrot and on colonization of potato roots by AMF. The differential effects on colonization occurred in the presence of a microbial community. Our results show that these two important groups of rhizosphere microorganisms indeed interact with each other. Such interactions could potentially lead to synergistic effects between the two groups but this could depend on whether the bacteria truly solubilize phosphate in the rhizosphere in the presence of microbial communities.

Composition andffunction of the microbial commuity related with the nitrogen ccycling on the potato rhizosphere / Composición y función de la comunidad microbiana relacionada con el ciclaje de nitrógeno en la rizosfera de Solanum tuberosum (BAHUIN) grupo phureja

In the S. tuberosum group phureja crops, mineral fertilizer and organic amendments are applied to meet the plants´ nutritional demands, however the effect of such practices on the associated rizospheric microbial communities are still unknown. Nitrogen plays an important role in agricultural production, and a great diversity of microorganisms regulates its transformation in the soil, affecting its availability for the plant. The aim of this study was to assess the structure of microbial communities related with the N cycle of S. tuberosum group phureja rizospheric soil samples, with contrasting physical-chemical properties and fertilization strategy. Few significant differences between the community composition at the phylum level were found, only Planctomycetes phylum was different between samples of different soil type and fertilization strategy. However, the analysis of nitrogen-associated functional groups made by ribotyping characterization, grouped soils in terms of such variables in a similar way to the physical-chemical properties. Major differences between soil samples were typified by higher percentages of the ribotypes from nitrite oxidation, nitrogen fixation and denitrification on organic amendment soils. Our results suggest that, the dominant rhizosphere microbial composition is very similar between soils, possibly as a result of population´s selection mediated by the rhizosphere effect. However, agricultural management practices in addition to edaphic properties of sampled areas, appear to affect some functional groups associated with the nitrogen cycling, due to differences found on soil´s physicalchemical properties, like the concentration of ammonium that seems to have an effect regulating the distribution and activity of nitrogen related functional groups in the S. tuberosum rhizosphere.

Fertilización mineral y enmiendas orgánicas son aplicadas para satisfacer las demandas nutricionales de los cultivos de S. tuberosum grupo phureja . Sin embargo, el efecto de esas prácticas sobre la comunidad microbiana asociada a la rizósfera aún no se conocen. El nitrógeno juega un papel importante en la producción agrícola y una gran diversidad de microorganismos regulan su transformación en el suelo, afectando su disponibilidad para la planta. El objeto de este estudio fue determinar la composición de la comunidad microbiana de la rizósfera de S. tuberosum grupo phureja , asociada con el ciclo del nitrógeno, en muestras de suelo contrastantes en sus propiedades fisicoquímicas y estrategia de fertilización. Pocas diferencias significativas entre la composición de la comunidad microbiana a nivel de phylum fueron encontradas, Í°nicamente el phylum Planctomycetes fue diferente entre las muestras de suelos con estrategias de fertilización diferentes. Sin embargo, el análisis de grupos funcionales asociados al nitrógeno llevado a cabo por la caracterización de ribotipificación, agrupó los suelos en términos de esas variables en una forma similar a las propiedades fisicoquímicas del suelo. Diferencias mayores entre las muestras de suelo fueron tipificadas por los altos porcentajes de ribotipos asociados a la oxidación de nitrito, fijación de nitrógeno y denitrificación sobre los suelos con enmiendas orgánicas. Nuestros resultados sugieren que la composición microbiana dominante es muy similar entre suelos, posiblemente como resultado de la selección de poblaciones mediada por el efecto rizosférico. Sin embargo, las prácticas del manejo agrícola en conjunto con las propiedades del suelo en las áreas muestreadas, parecen afectar algunos grupos funcionales asociados con el ciclo de nitrógeno, debido a las diferencias encontradas en las propiedades fisicoquímicas del suelo, como la concentración de amonio que parece tener un efecto regulando la distribución y actividad de los grupos funcionales relacionados con el ciclo del nitrógeno en la rizosfera de S. tuberosum.

Cultivable bacteria populations associated with leaves of banana and plantain plants and their antagonistic activity against Mycosphaerella fijiensis.

Mycosphaerella fijiensis is the etiological agent of Black Sigatoka, a fungal disease that affects production of banana and plantain crops in tropical regions. The sizes of cultivable epiphytic and endophytic bacterial populations, aerobic endospore forming bacteria (AEFB), and antagonist bacteria against M. fijiensis isolated from three Musa spp. cultivars from Urabá (Colombia) were studied, in order to find a suitable screening strategy to isolate antagonistic bacteria. Most of the variability found in the epiphytic and endophytic bacterial community sizes among fruit trees was explained by the cultivar differences. We found population sizes ranging from 1.25 × 10(3) to 9.64 × 10(5) CFU/g of fresh leaf and found that 44 % of total cultivable bacteria belong to the AEFB group. We isolated 648 AEFB from three different cultivars and assessed their antagonistic activity against M. fijiensis using the cell-free supernatant obtained from bacterial liquid cultures in three different in vitro assays. Five percent of those bacteria showed higher percent inhibition than the positive control Bacillus subtilis UA321 has (percent inhibition = 84 ± 5) in the screening phase. Therefore, they were selected as antagonistic bacteria against the pathogen. The strains with the highest percentage of antagonism were found in older leaves for the three cultivars, given support to recommend this group of leaves for future samplings. Some of these isolated bacteria affected the mycelium and ascospores morphology of the fungus. They also presented in vitro characteristics related to a successful colonization of the phylloplane such as indolic compounds, surfactant production, and biofilm formation, which makes them possible, potential candidates as biological control agents.

Reseña del libro: propiedad intelectual en la era de los cultivos transgénicos: [revisión] / Book review: intellectual property in the era of transgenic crops: [review]

El libro Propiedad intelectual en la era de los cultivos transgénicos consta de nueve capítulos en los cuales el profesor Alejandro Chaparro y varios miembros de su grupo de investigación desarrollan en una estructura clara y comprensible el tema de la propiedad intelectual en el área de la Biotecnología. Este es un tema de gran relevancia para investigadores nacionales e internacionales en el área de ciencias de la vida, que pretendan hacer una contribución al conocimiento de la diversidad de nuestro país...